Ontime Health

Circadian and Fasting Research

Evidence from research into intermittent fasting more accurately described as time restricted feeding has lead to many insight on human health diet and nutrition

Cope with Stress, Best 6 Methods

tips for reducing stress

In our society stress, anxiety, and depression are common and often related issues that affect more than 50 percent of adults. While certain levels of stress are part of life and can even be a positive force that motivates you to react quickly during emergencies, too much stress, too often is not. Additionally, research shows that firefighters have triple the risk of stress disorders. During an immediate crisis, you need the stress hormones adrenaline and cortisol to pump you up. However, that same response during non-emergency moments, such as being stuck in traffic, in a line at the bank, or while having dinner with your family can have detrimental effects on your health.

Often, stress in firefighters presents as post-traumatic stress disorder (PTSD), which occurs after repeated exposure to traumatic, dangerous, and potentially life-threatening events that come hand-in-hand with the work you do. Untreated, chronic stress or worry, anxiety, depression, and/or PTSD is shown to increase the risk of in heart disease, high blood pressure, osteoporosis, diabetes, cancer, strokes, obesity, diabetes, metabolic syndrome, insomnia, excessive fatigue, unwanted weight gain or weight loss, difficulty concentrating, panic attacks, irritable bowel syndrome (IBS), indigestion, abdominal pain, substance abuse, alcoholism, and mortality.

Learning strategies to manage chronic stress and other stress disorders can decrease your risk of these symptoms and improve happiness, relaxation, and overall better health. Unfortunately, studies that look at firefighters and stress issues, also indicate that many don’t seek treatment because of concerns about stigma.

It’s not a happy picture. Think about what can happen when you put a car under an extreme amount of stress—if you drive an automobile long distances for excessive periods of time, in extreme temperatures without stopping, getting gas, changing the oil, or following other standard maintenance practices your car will break down earlier than it would if you gave it some TLC. Not just your body needs rest and care, so does your mind, especially when it comes to stress. Under excessive tension, you can overheat, run out of “fuel,” or burn up your own “engine.” It’s exhausting.

Negative Effect of Stress

  • Too much stress hurts your physical, emotional, and mental health.
  • Firefighters have 3 times the risk of stress issues compared to the general public.
  • You can lower your stress level by incorporating a social Mediterranean lifestyle.
  • Your stress response is naturally higher in the first half of the day, and decreases at night.
  • Healthy sleep, mindfulness, exercise, and diet can all help you to decrease stress.

How can I lower my stress level?

Thankfully, there are many simple strategies you can employ to reduce and treat stress and to bring your emotional health back into balance. Here’s how:

  • Live a Mediterranean Lifestyle: Studies of the people who live a Mediterranean lifestyle show that these leisure activities and social interactions reduce stress, anxiety, and depression. The Mediterranean lifestyle can help. Why? Because it’s more than just a diet, it’s a way of life. These cultures prioritize and include a great deal of social interaction—most meals are shared with family and friends, people spend more time outdoors getting fresh air and sunshine, and they are more likely to leisurely walk or bike to the market or to attend to other errands.
  • Understand Your Stress Clock: Certain glands in your body are responsible for producing and releasing the stress hormones that help you to be alert, and also to respond to stressful experiences. These glands follow a schedule of a sort that is influenced or “set” by light, sleep, activity, diet, and stressful events. In the past, humans slept at night when it was dark and were active during the daylight hours. Your stress clock is made to work according to this natural schedule, but that’s no longer how we live. Today’s modern world, especially for a firefighter, regularly and repeatedly requires you to manage an atypical exposure to light. You are often awake during naturally dark hours (shift work), and stressful situations during these night time hours is harder on your body. Why? Cortisol and adrenaline are both naturally more responsive and active during the earlier part of the day, and less so at night (when you might need them). You can’t rest and recover if your stress hormones are elevated, but you might need your stress response at night if a call comes over the line. You can combat this disruption to your stress response by taking steps to get restful sleep for seven to nine hours at night whenever you are not at work.
  • Exercise: Doing any exercise for 30-minutes to an hour a day helps your body to better respond to and recover from stress without it hurting your mind or body.
  • Be Mindful: Being mindful is the ability to be—mentally and physically—to be fully conscious and aware in the present moment. What are you thinking about right now? It’s likely that you’re reviewing a scenario of something that already happened, or you’re busy creating a mental to-do list for what needs to be done in the future. To some extent, this is perfectly natural. Our minds are made to evaluate and plan. It’s one of the reasons the human animal has survived for so long. However, if you spend all your time in the past or future, you leave no space to check in with the now, and this both elevates stress and leaves you unaware of your emotional balance. Awareness of the stress you are experiencing is the first step to letting it go. Some cultures are better at cultivating this state of now-ness than others by encouraging meditation, and mind-body exercises such as yoga or tai chi are a regular daily activity. All of these activities have been shown to lower stress and improve mood. Our culture could take some lessons from these. You can reduce stress by learning to meditate, practicing relaxation techniques, and including mind/body practices.
  • Slow Down: “I’m too busy!” It’s the number one excuse that people give for not taking the time to get enough sleep, exercise, or to prepare healthy meals. On the flip side, prioritizing these activities gives you more time in your day because slumber, physical activity, and eating healthy lowers stress and increases energy while improving emotional balance and stability. On your days off incorporate a ritual of meditating or just breathing slowly and deeply—even 5 minutes can help you to reset your mindset and lower stress—then move on to prioritizing your sleep, exercise, and healthy eating.
  • Get Outside Help: Sharing your worries or concerns with family and friends helps you to lower stress, but that’s not all you can do. We go and get a physical from our doctor once a year—your mental health is just as important. If you are suffering from one or all of these conditions, and it is affecting your daily life, do consider checking out some cognitive-behavioral therapy. It’s been shown to help address and reduce these symptoms.


8 Essential Healthy Eating Habits

8 tips for mindful eating

Sometimes the simplest way to define something is by stating what it is not. Food is fuel. The purpose of eating is to nourish our bodies and give them needed energy, both physically and mentally, to function each day. Using food as a way of altering, soothing, or suppressing feelings is not how your body was designed to use food. Unfortunately, it’s estimated that somewhere around, oh, ALL of us eat emotionally from time to time. Let’s face it, the majority of us do find pleasure in food, and there’s nothing wrong with this. Eating emotionally turns into the enemy when you use it as a regular coping strategy in your day-to-day life.

Why is this bad? Emotional or mind-less eating increases your risk of obesity and overweight, and with those two comes an increased risk of Type 2 diabetes, heart disease, cancer, chronic stress, stroked, and respiratory problems. So, if you eat to serve a purpose other than hunger, you can be reasonably confident that you are engaging in emotional eating. Both major and minor life events can trigger unconscious eating. Bored at work? Check. Going through a divorce? Check.

In fact, sometimes it is the mundane to-do lists that lead to the candy bars, not extreme emergencies. As you probably know, when you are responding to a high-intensity call you have no time to think about eating or being hungry. That’s because your brain and body have tapped into your fight/flight mode, which takes all your attention and leaves no room for noshing on the community donuts. But after it’s all over? Pass the hot wings and beer.

  • When you eat without paying attention you are much more likely to eat more than your body requires and to eat when you are not truly hungry. Both increase your risk for overweight and obesity.
  • Emotional or Stress eating leads to an increased risk of Type 2 diabetes, heart disease, cancer, and more.
  • It’s easy to incorporate strategies for more mindful eating including distraction-free eating, trigger awareness, feeling feelings, and knowing how to H.A.L.T.

The other downside to emotional eating is that when you eat in response to stress, sadness, or anger, you don’t usually crave a salad or steamed veggies. People tend to seek high-calorie, high-fat foods when stressed—and major bummer—our bodies store more of the food we eat as fat when we are stressed, compared to when we are relaxed.

How to eat mindfully: People who eat mindfully, but not emotionally or when distracted, are less likely to overeat. Mindful eating has also been linked to better health, less stress, and improved mood. How do you do it? Here are a few simple strategies.

  • Ditch distractions. Avoid multitasking while you eat. That means getting away from your laptop, turning off the television, and even waiting until a stressful meeting ends (you know, the ones that come with a box of donuts). Pay attention to what you are about to eat. Remember to use the myCircadianClock app to take a picture of anything you eat or drink. Just this simple act will help you to be conscious of what you’re eating.
  • Sit down. And not in your car. Munching while you cook dinner or make the kids’ lunches for tomorrow is a great recipe for overeating. It’s easy to unconsciously graze without noting when you have had enough to eat and this can cause eating too many calories overall. Sitting down at a table away from screens (smartphones included) allows you to feel the subtle shift between being stated over being stuffed. Plus, it takes around 20 minutes for an empty stomach to register food, so eat slowly as well.
  • Be Social. The Mediterranean diet includes a social lifestyle. That means enjoying at least one meal a day with other people. Having a chance to discuss your day or your plans for the day is a great way to relieve stress, and less stress means less overeating. Just be sure to save emotionally triggering conversations for after dinner.
  • Know Your Triggers. Many cultures and families express love and caring with food and eating. The first step to breaking a bad habit is to know the cues that cause it in the first place. Once you can pinpoint the fact that you always overeat at the In-Laws, you can make other arrangements. Maybe suggest a walk instead of a dinner. Or volunteer to be the dishwasher or server for an evening. Keep your hands busy doing non-food activities.
  • Incorporate Non-Food Pleasures. Mindful eating is not a diet. It is the intention of eating with awareness. With that in mind, make sure that you incorporate non-food activities you enjoy. As children, we all naturally know that we need to play, but we lose this instinct as adults. It is just as important. This harkens to the “be social” tip above and takes it a step further. Can you remember the last time you laughed with another person? Create a “play date” at least once a week with a friend or friends to do something unnecessary and fun. Play catch. Walk the dog. Go see a standup comedian.
  • Feel Your Feelings. Don’t feed your feelings. There is a difference between feeling emotionally down or “empty” and being truly hungry. This is a subtle signal, and one that many of us have lost because we’ve been taught to eat at set times of the day, or all day, rather than listen to hungry signals that our bodies give off when they need food. The good news is that you can turn the sound back up on these alarm clocks by simply tuning in to hunger and fullness. Before you put a morsel in your mouth, pause and ask yourself how you are feeling. If the answer is anything other than calm or serene, take it a step further and check in with your hunger. When is the last time you ate? How did you sleep last night? Are you just coming off of a stressful event? Are you nearing the end of a mundane day of paperwork? Know your triggers. Awareness is usually the first step in breaking the pattern of emotional eating.
  • Love Yourself. I know, hippy-dippy, but it is true that when we are feeling down about ourselves, we are much more likely to reach for unhealthy food or to eat when we are not hungry. Remember H.A.L.T. which stands for hungry, angry, lonely, or tired. In recovery groups, this is a popular acronym that you can use to spot check your level of emotional balance. If you are feeling an extreme of any of these, try to address it (or at the very least, acknowledge it)-don’t feed it.
  • Don’t Get Too Hangry. After all that, last but not least is that you don’t want to let yourself starve. Just like the H.A.L.T. acronym above alludes to, getting into any extreme one of these situations can make you “hangry.” And you and your partner, and those who love you, do not want you to be Hangry.

Love Your Liver to Live Longer

healthy food for liver

You can’t live without your liver and if you don’t keep it healthy you put yourself at an increased risk for liver diseases that can affect your entire body and life with symptoms that include abdominal pain and swelling, swelling of the legs and ankles, itchy skin, chronic fatigue, nausea, diarrhea, and the tendency to bruise easily. More severe symptoms include excessive sleepiness, mental confusion, coma, and death. Thankfully, your liver can repair and regenerate itself, and there are many lifestyle strategies you can incorporate to improve liver health. At around three pounds, the liver is the second largest organ inside your body (your skin is number one).

What does the liver do?

This football-sized organ sits in the upper right portion of your abdomen and is responsible for many essential functions in your body. These include:

  • Removing toxins from the blood.
  • Helping to digest and filter foods, beverages, vitamins, minerals, and medications.
  • Storing fuel in the form of sugar (glycogen) and fat.
  • Producing bile needed for digestion.
  • Assisting with blood clotting.

While liver disease can have many causes, it usually starts as inflammation of the liver that can be caused by poor diet, toxins, chemicals, viruses, bacterial infections, and parasites. All forms of inflammation will disrupt and limit normal liver function. Usually, people associate liver disease with excessive alcohol consumption, but the most significant risk for liver disease today may be the epidemic of diabetes and obesity. When you continuously and excessively drink alcohol or overeat, fat builds up in your liver, called Alcoholic fatty liver disease and Nonalcoholic fatty liver disease (NALFD) respectively. It’s estimated that as many as 25 percent of American adults have some degree of fatty liver disease. Those who are obese or diabetic are 70 to 90 percent likely to suffer from the condition, which occurs when your liver accumulates too many fat cells and causes inflammation. Untreated, both types of fatty liver disease can lead to fibrosis, cirrhosis, or liver cancer.

Your Liver and Digestion: One critical liver function is with the digestive system. When blood comes to the liver from your digestive organs, it carries the nutrients, medications, and toxic substances you have consumed. In the liver, substances are processed, saved, transformed, cleansed, removed, and/or absorbed. Once your liver has discerned what needs to go where, it either returns the materials to your blood or the liver will release the waste to your intestines to be eliminated. Each macronutrient is handled differently:

  • Fats: Your body needs bile (a brown, green digestive liquid that’s produced by your liver) to break down and absorb the fats you eat.
  • Carbs: Eating carbs signals the hormone insulin, which ushers sugar into your cells. Your liver stores excess sugar that is not used by cells as glycogen. Excess sugar will be made into fat that is then stored in other cells of your body.
  • Proteins: Your liver changes amino acids into energy your body can use, or it transforms them into carbs or fats. Ammonia is a harmful byproduct of amino acids. A healthy liver converts ammonia into urea, which is then released as waste in your urine.
  • Vitamins and Minerals: Your liver stores vitamins and minerals and releases them into your blood when your body needs them.

How can I improve the health of my liver?

  • Eat Healthy: You can protect and repair your liver with a healthy diet. Follow the Mediterranean way of eating and living, which includes plenty of fresh vegetables and fruits, olive oil, nuts and seeds, fish, and whole grains. Avoid trans fats, overly processed, and high sugar foods.
  • Limit Alcohol: If you drink alcohol, drink it in moderation (one drink a day for women, two for men).
  • Follow Medication Directions: Take medication as prescribed and talk to your doctor about herbal remedies (some can damage your liver). Taking too much prescription or nonprescription drugs overloads the liver. Don’t mix medicines with alcohol.
  • Get Moving: Include exercise, which can help you lose weight and reduce fat in your liver. If you want suggestions for putting together an entire training regimen you can find some great ideas at the Seattle Fire Department website, at FireFit Program, at 555 Fitness, or for some extra motivation consider joining a challenge designed for firefighters.

Effects of Light on Sleep and Circadian Rhythm

improving sleep quality

Light can have a profound impact on our sleep. Exposure to light can stimulate wakefulness and alertness, whereas darkness can lead to sleepiness. This is because light acts as a signal for your circadian rhythm, the body’s 24-hour biological clock. 

By understanding how light can influence our body’s biological rhythms, you can control your light exposure to ensure optimal sleep quality and overall health. 

How does light affect sleep?

Light has a direct effect upon our feelings or alertness or sleepiness. Exposure to light makes us feel awake, alert and increases our ability to concentrate, whereas darkness can promote drowsiness and sleepiness. 

When we are exposed to natural light from the sun, our body’s internal clock, known as circadian rhythm, becomes aligned with daylight hours. Circadian rhythms are the body’s 24-hour natural clocks that play an important role in the timing and quality of sleep. If you have ever experienced jet lag, you will know how powerful these rhythms can be. 

Circadian rhythms control many mental and physical processes, such as: 

  • Body temperature
  • Hormone levels
  • Sleep-wake cycle
  • Alertness and drowsiness 

How does light affect circadian rhythm?

When light hits your eyes, it is detected by specialized cells in the retina that carry a signal to a part of the brain called the suprachiasmatic nucleus (SCN). The SCN uses this information to tell the time of day, and this information is transmitted to various organs of the body.

The absence of light sends a signal to the body that it’s time to rest through the release of melatonin, the ‘sleep hormone’, from the pineal gland in the brain. The release of melatonin signals the brain and body that it is time to sleep by inducing physiological changes including muscle relaxation and a decrease in body temperature. 

Melatonin levels rise during the evening and reach a peak around 3 a.m., before decreasing in the morning and remaining low during the day. However, nighttime light exposure reduces melatonin suppression, making it harder to fall asleep. In this way, light is an important signal for circadian rhythm that controls the biological and mental changes that occur over a 24-hour period. 

Other signals for circadian rhythm

Besides light, there are several additional signals that the brain uses to control circadian timing, known as ‘zeitgebers’. These environmental cues are used by the body to determine the time of day, and include:

  • Food intake
  • Sleep timing
  • Exercise timing 

How is light measured?

Light is often measured in a unit called lux, which is often referred to as ‘incident light’. This unit of measurement takes into account the brightness of the light source, and your distance from it. 

Lux can be used to measure both natural and artificial light. On a bright day in summer, the outside environment may be 150,000 lux. On a cloudy day, this can fall to 1000 lux. At night, the outside environment drops to below a single lux. 

On the other hand, a well-lit house may register up to 500 lux. In the evening, it is important to dim lights to less than 200 lux to help your body prepare for bed. When you turn off the lights before sleep, you should ensure your bedroom has no more than 5 lux. 

Sleep cycles and light exposure

Sleep is not a uniform process. In a normal night of sleep, you will go through between four to six sleep cycles, each lasting 90-120 minutes. Each cycle is made up of 4 different stages: two stages of light sleep, one stage of deep sleep and one stage of rapid eye movement (REM) sleep.

Light exposure of above 100 lux at night can lead to negative effects on sleep quality, and the transition between sleep cycles. In addition, light stimuli can lead to a shorter total period of time in the deeper, more restorative stages of sleep including REM sleep. 

Effects of artificial light on health

In modern society we often use electronic devices such as phones, laptops and tablets that emit artificial light. Using these technologies at nighttime can negatively affect our circadian rhythm. This is a relatively new problem in human history, following the advent of electricity in the 20th century. 

Excessive exposure to artificial light at night can interfere with circadian rhythm and have negative effects on human health, leading to complications such as:

In fact, one small study showed that just 100 lux of constant light at night resulted in higher heart rate and poorer blood glucose control. Therefore, it is important to limit light levels at night as much as possible.

Should I sleep in total darkness?

It is generally best to sleep in an environment that is as dark as possible, as pitch darkness helps to ensure your body is not signaled to wake up during the night. 

Even with your eyelids closed, light still can enter your eye and disrupt your sleep. Therefore, make sure your bedroom is as dark as possible before you go to sleep. Sleeping in a dark environment can have the following benefits: 

  • Reducing eye strain: a dark bedroom that minimizes ambient light can reduce eye strain.
  • Avoiding weight gain: light stimulus at night can interfere with your body’s metabolism, increasing the risk of weight gain. One study showed that women exposed to ambient light from a TV gained 10 pounds or more over five years. 
  • Reduced cancer risk: there may be a link between houses with high levels of artificial light and risk of cancer, according to some research. However, more research is needed to verify this effect. 

Due to the many benefits of minimizing light exposure whilst sleeping, it is important to keep your bedroom as dark as possible at night. 

How to keep your bedroom dark

Many people sleep in a bedroom that is penetrated by some form of artificial light, from electronic devices, intrusive streetlights, or the TV. However, it is important to reduce light as much as possible in your bedroom, to help you sleep. 

A few simple tips to make your bedroom more suitable for sleep include: 

  • Cover windows with thick curtains to block streetlight, e.g. using blackout curtains
  • Turn off electronic equipment that emits light
  • Wear an eye mask to further reduce light exposure 

Building a sleep routine around light

Because light is a powerful signal for sleep, it is important to build a sleep routine that involves a gradually darkening environment. This ensures ideal light conditions to align your circadian rhythm with the darkness at night.

This could involve the following steps: 

  • Install dimmer switches to reduce the amount of light you receive at night, and use the dim setting when the sun sets
  • Turn off electronic devices 2 hours before you plan to sleep 
  • If you must use an electronic device, turn down the brightness and turn on ‘night mode’ to reduce emitted blue light. 
  • Using a red light if you need to move around at night, as red wavelengths have been shown to be less disruptive to sleep

How to use light to optimize circadian rhythm

In addition to building a sleep routine around light, you can also ensure your circadian rhythm is healthy and aligned through monitoring light you receive during the day. The brightness and type of light, amount of timing exposed to light, and timing of exposure can all help to build a strong circadian rhythm. 

The following tips can help you to ensure you receive the optimal light exposure during the day:

  • Get 30 minutes of direct sunlight as soon as you can after waking up. Ideally, spend this time outside e.g. on the front porch. 
  • If you are unable to go outside in the morning, consider eating breakfast or drinking your morning coffee near a bright window.
  • Consider purchasing a light box to increase light exposure if you do not have access to natural light in your home. This is a form of light therapy using an electric light can help realign your circadian rhythm.
  • If you exercise during the day, try to do so outside if convenient to help receive more daytime light exposure.

Circadian rhythm sleep disorders

Circadian rhythm sleep disorders are a cluster of sleep disorders that are characterized by a misaligned circadian rhythm. These conditions may be caused by disrupted light signals during the day and at night, as well as shift work or flying across time zones.

Symptoms of circadian rhythm sleep disorders include difficulty falling asleep, fatigue during the day, and sleep deprivation. The most common circadian rhythm sleep disorders include: 

  • Delayed phase sleep disorder: most common in adolescents, this condition is when you go to sleep and wake up significantly later than what is typical. Generally, you have this condition if you regularly go to sleep at 2 a.m. or later. People with this condition may feel lazy and unproductive during the day, but energized and creative at nighttime. 
  • Advanced sleep phase disorder: this condition is when you fall asleep earlier than you would like (e.g. 6-8 p.m.) and wake up particularly early (e.g. 3-5 a.m.) on a regular basis. This condition is most common amongst the elderly. 
  • Jet lag: this involves your body’s circadian rhythm being synced with your departing destination’s time zone, rather than your current time zone. This can make it difficult to function in the new time zone, and you may experience gastrointestinal issues.


Light and dark has a powerful impact upon sleepiness, alertness, and a direct effect on the circadian clock. Your body responds to light signals to guide feelings of being awake or subjective sleepiness.

To ensure you have optimized your circadian rhythm, ensure to get light exposure during the day. At night, try to minimize the use of electronic screens 2 hours before sleep and ensure your bedroom is dark. These steps can help to ensure your circadian phase is aligned with the rising and setting of the sun, to promote optimal sleep. 

Improving your sleep quality and circadian system can prevent excessive body mass gain, and other negative health effects. 


  1. Lunn, R.M., Blask, D.E., Coogan, A.N., Figueiro, M.G., Gorman, M.R., Hall, J.E., Hansen, J., Nelson, R.J., Panda, S., Smolensky, M.H. and Stevens, R.G., 2017. Health consequences of electric lighting practices in the modern world: A report on the National Toxicology Program’s workshop on shift work at night, artificial light at night, and circadian disruption. Science of the Total Environment, 607, pp.1073-1084. https://www.sciencedirect.com/science/article/abs/pii/S004896971731759X        
  2. Panda, S., Hogenesch, J.B. and Kay, S.A., 2002. Circadian rhythms from flies to human. Nature, 417(6886), pp.329-335. https://www.nature.com/articles/417329a
  3. Hatori, M., Gronfier, C., Van Gelder, R.N., Bernstein, P.S., Carreras, J., Panda, S., Marks, F., Sliney, D., Hunt, C.E., Hirota, T. and Furukawa, T., 2017. Global rise of potential health hazards caused by blue light-induced circadian disruption in modern aging societies. NPJ aging and mechanisms of disease, 3(1), pp.1-3. https://www.nature.com/articles/s41514-017-0010-2
  4. Clark, D.D., Gorman, M.R., Hatori, M., Meadows, J.D., Panda, S. and Mellon, P.L., 2013. Aberrant development of the suprachiasmatic nucleus and circadian rhythms in mice lacking the homeodomain protein Six6. Journal of biological rhythms, 28(1), pp.15-25. https://journals.sagepub.com/doi/full/10.1177/0748730412468084
  5. Deota, S. and Panda, S., 2021. New Horizons: Circadian control of metabolism offers novel insight into the cause and treatment of metabolic diseases. The Journal of Clinical Endocrinology & Metabolism, 106(3), pp.e1488-e1493. https://academic.oup.com/jcem/article-abstract/106/3/e1488/5912272
  6. Godfrey, S., Iversen, H.K. and West, A.S., 2022. Melatonin profile in healthy, elderly subjects-A systematic literature review. Chronobiology International, 39(4), pp.476-492. https://www.tandfonline.com/doi/abs/10.1080/07420528.2021.2016794
  7. Bonmati-Carrion, M.A., Arguelles-Prieto, R., Martinez-Madrid, M.J., Reiter, R., Hardeland, R., Rol, M.A. and Madrid, J.A., 2014. Protecting the melatonin rhythm through circadian healthy light exposure. International journal of molecular sciences, 15(12), pp.23448-23500. https://www.mdpi.com/1422-0067/15/12/23448
  8. Sharma, V.K. and Chandrashekaran, M.K., 2005. Zeitgebers (time cues) for biological clocks. Current Science, pp.1136-1146. https://www.jstor.org/stable/24110966
  9. Middleton, B., Stone, B.M. and Arendt, J., 2002. Human circadian phase in 12: 12 h, 200:< 8 lux and 1000:< 8 lux light-dark cycles, without scheduled sleep or activity. Neuroscience letters, 329(1), pp.41-44. https://www.sciencedirect.com/science/article/abs/pii/S0304394002005748
  10. Stanley, N., 2005. The physiology of sleep and the impact of ageing. European Urology Supplements, 3(6), pp.17-23. https://www.sciencedirect.com/science/article/pii/S156990560580003X
  11. Tähkämö, L., Partonen, T. and Pesonen, A.K., 2019. Systematic review of light exposure impact on human circadian rhythm. Chronobiology international, 36(2), pp.151-170. https://www.tandfonline.com/doi/full/10.1080/07420528.2018.1527773
  12. Lie, J.A.S., Kjuus, H., Zienolddiny, S., Haugen, A., Stevens, R.G. and Kjærheim, K., 2011. Night work and breast cancer risk among Norwegian nurses: assessment by different exposure metrics. American journal of epidemiology, 173(11), pp.1272-1279. https://pubmed.ncbi.nlm.nih.gov/21454824/
  13. Asaoka S, Aritake S, Komada Y, Ozaki A, Odagiri Y, Inoue S, Shimomitsu T, Inoue Y. Factors associated with shift work disorder in nurses working with rapid-rotation schedules in Japan: the nurses’ sleep health project. Chronobiol Int. 2013 May;30(4):628-36. doi: 10.3109/07420528.2012.762010. Epub 2013 Feb 27. PMID: 23445510. https://pubmed.ncbi.nlm.nih.gov/23445510/
  14. Folkard S, Lombardi DA, Tucker PT. Shiftwork: safety, sleepiness and sleep. Ind Health 2005 Jan;43(1):20-3. doi: 10.2486/indhealth.43.20. PMID: 15732299. https://pubmed.ncbi.nlm.nih.gov/15732299/
  15. Roenneberg T, Allebrandt KV, Merrow M, Vetter C. Social jetlag and obesity. Curr Biol. 2012 May 22;22(10):939-43. doi: 10.1016/j.cub.2012.03.038. Epub 2012 May 10. Erratum in: Curr Biol. 2013 Apr 22;23(8):737. PMID: 22578422. https://pubmed.ncbi.nlm.nih.gov/22578422/
  16. Wong PM, Hasler BP, Kamarck TW, Muldoon MF, Manuck SB. Social Jetlag, Chronotype, and Cardiometabolic Risk. J Clin Endocrinol Metab. 2015 Dec;100(12):4612-20. doi: 10.1210/jc.2015-2923. Epub 2015 Nov 18. PMID: 26580236; PMCID: PMC4667156. https://pubmed.ncbi.nlm.nih.gov/26580236/
  17. Mason, I.C., Grimaldi, D., Reid, K.J., Warlick, C.D., Malkani, R.G., Abbott, S.M. and Zee, P.C., 2022. Light exposure during sleep impairs cardiometabolic function. Proceedings of the National Academy of Sciences, 119(12), p.e2113290119. https://www.pnas.org/doi/10.1073/pnas.2113290119
  18. Figueiro, M.G. and Rea, M.S., 2012. Preliminary evidence that light through the eyelids can suppress melatonin and phase shift dim light melatonin onset. BMC Research Notes, 5(1), pp.1-9. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3469368/
  19. Zhu, L. and Zee, P.C., 2012. Circadian rhythm sleep disorders. Neurologic clinics, 30(4), pp.1167-1191. https://www.neurologic.theclinics.com/article/S0733-8619(12)00052-7/abstract
  20. Sack, R.L., Auckley, D., Auger, R.R., Carskadon, M.A., Wright Jr, K.P., Vitiello, M.V. and Zhdanova, I.V., 2007. Circadian rhythm sleep disorders: part II, advanced sleep phase disorder, delayed sleep phase disorder, free-running disorder, and irregular sleep-wake rhythm. Sleep, 30(11), pp.1484-1501. https://academic.oup.com/sleep/article-abstract/30/11/1484/2696878
  21. Pavlova, M.K. and Latreille, V., 2019. Sleep disorders. The American Journal of Medicine, 132(3), pp.292-299. https://pubmed.ncbi.nlm.nih.gov/30292731/
  22. Sack, R.L., Auckley, D., Auger, R.R., Carskadon, M.A., Wright Jr, K.P., Vitiello, M.V. and Zhdanova, I.V., 2007. Circadian rhythm sleep disorders: part I, basic principles, shift work and jet lag disorders. Sleep, 30(11), pp.1460-1483. https://academic.oup.com/sleep/article-abstract/30/11/1460/2696877
  23. Desmet, L., Thijs, T., Segers, A., Verbeke, K. and Depoortere, I., 2021. Chronodisruption by chronic jetlag impacts metabolic and gastrointestinal homeostasis in male mice. Acta Physiologica, 233(4), p.e13703. https://onlinelibrary.wiley.com/doi/abs/10.1111/apha.13703

Best Time To Workout: Morning or Evening?

Best Time To Workout

By Jack Harley, MSc, University of Oxford 

Making time to exercise on a regular basis can be challenging, and usually finding any time to exercise is the most important thing. But if you want to get the most out of your workouts, when you exercise may also be important.

Regardless of the timing, there are many benefits of working out such as improved endurance and strength, lower blood pressure and decreased risk of chronic diseases such as type 2 diabetes.

However, choosing an appropriate time to exercise can boost physical performance, help with sleep, and improve your circadian rhythm. In many cases, finding the ideal time to workout can be as much about personal preference than about physiology. 

The advantages of working out in the morning compared to the afternoon or evening are discussed in this article. 

Working out in the morning

There are many benefits of working out in the morning. For the early birds, working out in the morning can be a preferred time, and may be associated with the following benefits: 

Increased fat loss

Research has shown that you burn more body fat on an empty stomach. Therefore, exercising before breakfast may allow you to burn more fat than exercising later in the day. However, the benefit of this form of ‘fasted cardio’ may only last a short period. 

Over the course of weeks or months, studies have shown that fat loss with or without having eaten a meal was the same. For example, one study randomly assigned women to receive either a 250-calorie shake or to fast before an aerobic workout, and fat loss was the same for both groups.

Better sleep 

Working out in the morning may lead to better sleep than working out in the afternoon or evening. One study in endurance athletes showed that those who exercised in the morning tended to sleep better by spending less time lying awake in bed than those who worked out in the evening. However, the research is not definitive, as some research has shown that evening exercise may also improve sleep. 

Improved circadian rhythm

Working out in the morning shifts your body clock earlier, meaning you will likely feel tired earlier, and wake up earlier the next day. This may help to align your circadian rhythm more closely with daylight hours. 

Easier to build a routine

Morning workouts may be easier to stick to. Research suggests that healthy habits in the morning are easier to maintain over a long period of time than those later in the day. This may be because many people generally have fewer commitments in the morning compared to later in the day. For example, one study showed that exercise adherence was slightly higher in individuals who worked out in the morning, compared to the afternoon. 

Improved pain management

Another benefit of working out in the morning is that it may help in managing chronic pain. Research has demonstrated that morning workouts are more effective in reducing bodily pain than evening workouts.

Improved productivity during the day

Working out triggers the release of hormones known as endorphins that uplift your mood, which can make you more productive and focused at work. As a result, energy levels, alertness and decision-making are increased following morning exercise.

Need for a longer warm up

While there are many benefits to morning workouts, you may need to warm up more thoroughly for morning workouts compared to afternoon or evening workouts. This is because core body temperature is generally lower, heart rate is lower, and your muscles may be tighter in the morning. Engaging in exercise when you are not fully warmed up may cause injury. Therefore, ensure you are fully warmed up before exercising in the morning.

Working out in the afternoon/evening 

If you are not an early bird, then it may be more beneficial for you to workout in the afternoon or evening. There are many benefits of working out later in the day, discussed below.

Improved performance

Workouts performed in the afternoon or evening may be associated with a performance boost, particularly for high-intensity exercise. Studies have shown that strength and flexibility levels are highest later in the day. 

One study showed that the body’s peak level of muscle force occurs in the afternoon.  In addition, a review of studies suggests that strength levels may be between 3% to 20% higher in the afternoon compared to the morning. This suggests that resistance training workouts such as lifting weights may be best performed at this time.

Aerobic exercise abilities may also be improved in the afternoon. One study showed that young men were able to cycle at a standard difficulty for 20% longer in the afternoon compared to the morning.

Lower risk of injury

Body temperature tends to be higher in the afternoon and evening, so your muscles may be already warmed up if you exercise at this time. Warmer muscles are associated with better exercise performance, and lower risk of injury

Workout feels easier

The perceived exertion of a workout is lowest for afternoon workouts, meaning the workouts feel physically easier at this time. This difference is attributed to circadian rhythm, the body’s biological clock that ebbs and flows over a 24-hour period.

Improved circadian rhythm

Although morning workouts may be best for resetting the biological clock, afternoon workouts may also be beneficial for improving circadian rhythm. Workouts performed between 1 p.m. and 4 p.m. may also help you overcome the afternoon slump and shift the body clock earlier in the same way as a morning workout. 

Increased muscle growth

Testosterone is an important hormone for muscle-building in men, and women, and your body may have higher levels of testosterone in the afternoon than morning. This suggests that muscle growth may be best achieved with afternoon exercise, although more research is needed to verify this. 

Metabolic benefits

Working out later in the day may help to improve metabolism, which is how the body converts food into energy. One small, 12-week study in pre-diabetic and diabetic men showed that workouts completed in the afternoon had better metabolic effects than those in the morning, including higher fat loss. 

Impact on sleep

Performing intense aerobic exercise within one hour of sleep may make it more difficult to fall asleep. However, performing aerobic exercise in the early evening (7 – 8 p.m.) has been shown not to disrupt sleep. In addition, studies have shown that lifting weights in the evening resulted in minimal sleep disturbance. Therefore, working out at night time may not be disruptive to sleep if at least 2 hours is given between the workout time and the 

Consistent timing is key

For the average person, the timing of workouts is less important than performing some exercise at all on a regular basis. However, for those that are able to workout regularly, working out at a consistent time may be important, according to research. This is because the timing of our workout can influence our circadian rhythm. Consistently working out at either the morning or evening on a daily basis may be more important than working out at 

Exercise and circadian rhythm 

The timing of exercise may be particularly important because exercise is a signal for circadian rhythm. Circadian rhythm describes the physical and mental changes that ebb and flow over a 24-hour cycle. Circadian rhythms control a range of bodily processes that occur over daily rhythms such as:

  • Hormone levels
  • Core body temperature
  • Alertness and drowsiness
  • Sleep-wake cycle

Circadian rhythms are controlled by the hypothalamus of the brain, which responds to signals in the environment to determine the time of day. These signals for circadian rhythm are known as ‘zeitgebers’, and include the following: 

  • Light and darkness
  • Meal timings
  • Sleep timing
  • Exercise 

Light is the most important signal for circadian rhythm, but the timing of exercise is also important. Your circadian rhythm uses the timing of physical exertion as a signal for determining the time of day, which is why working out at a consistent time may be beneficial. 

By adhering to a consistent workout schedule, you are training your body to accurately tell the time so it knows when to sleep and when to be awake.

Circadian rhythm and health

Improving circadian rhythm through a regular 24-hour cycle is important for overall health. This is because a disrupted circadian rhythm is associated with an increased risk of a range of negative health conditions such as:

By improving circadian rhythm, you can improve your overall health by improving sleep quality, and reducing the risk of chronic diseases. 

Is the best time to workout personal?

Some research shows that a person’s chronotype may influence the time of day that your optimal performance occurs. However, if your current workout schedule isn’t working, it is possible to change it. Research suggests that your body may adapt to regular exercise at different times of the day by altering your circadian rhythm. 

Therefore, any time of day you consistently have free time for physical activity may be the optimal time for you. Consistent timing of your training will help your fitness goals, whilst also improving your circadian rhythm. 

The takeaway

The science of when to exercise is still expanding, and there is no clear cut answer. Working out in the early morning can help you build a consistent routine, and sleep better at night, while the early or late afternoon or evening training may allow you to perform at your peak.

However, what’s clear is that working out is important, whenever it is done. Working out for 30 minutes per day can improve your physical and mental health, and reduce your risk of many diseases. 

In the end, it’s important to find a realistic workout schedule you can stick to, regardless of the exercise timing. It is also important to keep your workout regime at a consistent time, you may help realign your circadian rhythm.


1 .Cornelissen, V.A. and Fagard, R.H., 2005. Effects of endurance training on blood pressure, blood pressure–regulating mechanisms, and cardiovascular risk factors. Hypertension, 46(4), pp.667-675. https://www.ahajournals.org/doi/abs/10.1161/01.hyp.0000184225.05629.51

  1. Atan, T., Unver, S., Islamoglu, I. and Cavusoglu, G., 2017. Endurance performance according to Circadian Cycle. The Anthropologist, 27(1-3), pp.32-36. https://www.tandfonline.com/doi/abs/10.1080/09720073.2017.1311685
  2. Duglan, D. and Lamia, K.A., 2019. Clocking in, working out: circadian regulation of exercise physiology. Trends in Endocrinology & Metabolism, 30(6), pp.347-356. https://www.sciencedirect.com/science/article/abs/pii/S1043276019300657
  3. Aird, T.P., Davies, R.W. and Carson, B.P., 2018. Effects of fasted vs fedstate exercise on performance and postexercise metabolism: A systematic review and metaanalysis. Scandinavian journal of medicine & science in sports, 28(5), pp.1476-1493. https://pubmed.ncbi.nlm.nih.gov/29315892/
  4. Schoenfeld, B.J., Aragon, A.A., Wilborn, C.D., Krieger, J.W. and Sonmez, G.T., 2014. Body composition changes associated with fasted versus non-fasted aerobic exercise. Journal of the International Society of Sports Nutrition, 11(1), pp.1-7. https://jissn.biomedcentral.com/articles/10.1186/s12970-014-0054-7
  5. Ramos-Campo, D.J., Ávila-Gandía, V., Luque, A.J. and Rubio-Arias, J.Á., 2019. Effects of hour of training and exercise intensity on nocturnal autonomic modulation and sleep quality of amateur ultra-endurance runners. Physiology & behavior, 198, pp.134-139. https://pubmed.ncbi.nlm.nih.gov/30389476/
  6. Saidi, O., Colin, E., Rance, M., Doré, E., Pereira, B. and Duché, P., 2021. Effect of morning versus evening exercise training on sleep, physical activity, fitness, fatigue and quality of life in overweight and obese adults. Chronobiology International, 38(11), pp.1537-1548. https://pubmed.ncbi.nlm.nih.gov/34128447/
  7. Youngstedt, S.D., Elliott, J.A. and Kripke, D.F., 2019. Human circadian phase–response curves for exercise. The Journal of physiology, 597(8), pp.2253-2268. https://physoc.onlinelibrary.wiley.com/doi/full/10.1113/JP276943
  8. Chaix, A. and Panda, S., 2019. Timing tweaks exercise. Nature Reviews Endocrinology, 15(8), pp.440-441. https://www.nature.com/articles/s41574-019-0229-z
  9. Fournier, M., d’Arripe-Longueville, F., Rovere, C., Easthope, C.S., Schwabe, L., El Methni, J. and Radel, R., 2017. Effects of circadian cortisol on the development of a health habit. Health Psychology, 36(11), p.1059. https://psycnet.apa.org/record/2017-27629-001
  10. Schumacher, L.M., Thomas, J.G., Raynor, H.A., Rhodes, R.E. and Bond, D.S., 2020. Consistent morning exercise may be beneficial for individuals with obesity. Exercise and sport sciences reviews, 48(4), p.201. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7492403/
  11. Brooker, P.G., Gomersall, S.R., King, N.A. and Leveritt, M.D., 2019. The feasibility and acceptability of morning versus evening exercise for overweight and obese adults: A randomized controlled trial. Contemporary Clinical Trials Communications, 14, p.100320. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6348200/
  12. Küüsmaa-Schildt, M., Liukkonen, J., Vuong, M.K., Nyman, K., Häkkinen, K. and Häkkinen, A., 2019. Effects of morning vs. evening combined strength and endurance training on physical performance, sleep and well-being. Chronobiology International, 36(6), pp.811-825. https://pubmed.ncbi.nlm.nih.gov/30950283/
  13. Wheeler, M.J., Green, D.J., Ellis, K.A., Cerin, E., Heinonen, I., Naylor, L.H., Larsen, R., Wennberg, P., Boraxbekk, C.J., Lewis, J. and Eikelis, N., 2020. Distinct effects of acute exercise and breaks in sitting on working memory and executive function in older adults: a three-arm, randomised cross-over trial to evaluate the effects of exercise with and without breaks in sitting on cognition. British journal of sports medicine, 54(13), pp.776-781. https://bjsm.bmj.com/content/54/13/776
  14. Lunn, R.M., Blask, D.E., Coogan, A.N., Figueiro, M.G., Gorman, M.R., Hall, J.E., Hansen, J., Nelson, R.J., Panda, S., Smolensky, M.H. and Stevens, R.G., 2017. Health consequences of electric lighting practices in the modern world: A report on the National Toxicology Program’s workshop on shift work at night, artificial light at night, and circadian disruption. Science of the Total Environment, 607, pp.1073-1084. https://www.sciencedirect.com/science/article/abs/pii/S004896971731759X
  15. Chtourou, H. and Souissi, N., 2012. The effect of training at a specific time of day: a review. The Journal of Strength & Conditioning Research, 26(7), pp.1984-2005. https://journals.lww.com/nsca-jscr/Fulltext/2012/07000/The_Effect_of_Training_at_a_Specific_Time_of_Day_.33.aspx
  16. Racinais, S., 2010. Different effects of heat exposure upon exercise performance in the morning and afternoon. Scandinavian journal of medicine & science in sports, 20, pp.80-89. https://pubmed.ncbi.nlm.nih.gov/21029194/
  17. Chtourou, H. and Souissi, N., 2012. The effect of training at a specific time of day: a review. The Journal of Strength & Conditioning Research, 26(7), pp.1984-2005. https://journals.lww.com/nsca-jscr/Fulltext/2012/07000/The_Effect_of_Training_at_a_Specific_Time_of_Day__.33.aspx
  18. Hill, D.W., 2014. Morning–evening differences in response to exhaustive severe-intensity exercise. Applied Physiology, Nutrition, and Metabolism, 39(2), pp.248-254. https://cdnsciencepub.com/doi/10.1139/apnm-2013-0140#.XpXjYshKhPZ
  19. Harding, C., Pompei, F., Bordonaro, S.F., McGillicuddy, D.C., Burmistrov, D. and Sanchez, L.D., 2019. The daily, weekly, and seasonal cycles of body temperature analyzed at large scale. Chronobiology International, 36(12), pp.1646-1657. https://www.tandfonline.com/doi/abs/10.1080/07420528.2019.1663863?journalCode=icbi20
  20. Woods, K., Bishop, P. and Jones, E., 2007. Warm-up and stretching in the prevention of muscular injury. Sports medicine, 37(12), pp.1089-1099. https://link.springer.com/article/10.2165/00007256-200737120-00006
  21. Chtourou, H. and Souissi, N., 2012. The effect of training at a specific time of day: a review. The Journal of Strength & Conditioning Research, 26(7), pp.1984-2005. https://journals.lww.com/nsca-jscr/Fulltext/2012/07000/The_Effect_of_Training_at_a_Specific_Time_of_Day_.33.aspx
  22. Youngstedt, S.D., Elliott, J.A. and Kripke, D.F., 2019. Human circadian phase–response curves for exercise. The Journal of physiology, 597(8), pp.2253-2268. https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP276943
  23. Hayes, L.D., Bickerstaff, G.F. and Baker, J.S., 2010. Interactions of cortisol, testosterone, and resistance training: influence of circadian rhythms. Chronobiology international, 27(4), pp.675-705. https://pubmed.ncbi.nlm.nih.gov/20560706/
  24. Mancilla, R., Brouwers, B., SchrauwenHinderling, V.B., Hesselink, M.K., Hoeks, J. and Schrauwen, P., 2021. Exercise training elicits superior metabolic effects when performed in the afternoon compared to morning in metabolically compromised humans. Physiological Reports, 8(24), p.e14669. https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.14669
  25. Larsen, P., Marino, F., Melehan, K., Guelfi, K.J., Duffield, R. and Skein, M., 2019. Evening highintensity interval exercise does not disrupt sleep or alter energy intake despite changes in acylated ghrelin in middleaged men. Experimental physiology, 104(6), pp.826-836. https://physoc.onlinelibrary.wiley.com/doi/full/10.1113/EP087455
  26. Hauri, P., 1969. The influence of evening activity on the onset of sleep. Psychophysiology, 5(4), pp.426-430. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-8986.1969.tb02842.x
  27. Longo, V.D. and Panda, S., 2016. Fasting, circadian rhythms, and time-restricted feeding in healthy lifespan. Cell metabolism, 23(6), pp.1048-1059. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5388543/
  28. Panda, S., 2016. Circadian physiology of metabolism. Science, 354(6315), pp.1008-1015. https://www.science.org/doi/abs/10.1126/science.aah4967
  29. Hatori, M., Gronfier, C., Van Gelder, R.N., Bernstein, P.S., Carreras, J., Panda, S., Marks, F., Sliney, D., Hunt, C.E., Hirota, T. and Furukawa, T., 2017. Global rise of potential health hazards caused by blue light-induced circadian disruption in modern aging societies. NPJ aging and mechanisms of disease, 3(1), pp.1-3. https://www.sciencedirect.com/science/article/pii/S004896971731759X
  30. Lie, J.A.S., Kjuus, H., Zienolddiny, S., Haugen, A., Stevens, R.G. and Kjærheim, K., 2011. Night work and breast cancer risk among Norwegian nurses: assessment by different exposure metrics. American journal of epidemiology, 173(11), pp.1272-1279. https://pubmed.ncbi.nlm.nih.gov/21454824/
  31. Asaoka S, Aritake S, Komada Y, Ozaki A, Odagiri Y, Inoue S, Shimomitsu T, Inoue Y. Factors associated with shift work disorder in nurses working with rapid-rotation schedules in Japan: the nurses’ sleep health project. Chronobiol Int. 2013 May;30(4):628-36. doi: 10.3109/07420528.2012.762010. Epub 2013 Feb 27. PMID: 23445510. https://pubmed.ncbi.nlm.nih.gov/23445510/
  32. Folkard S, Lombardi DA, Tucker PT. Shiftwork: safety, sleepiness and sleep. Ind Health. 2005 Jan;43(1):20-3. doi: 10.2486/indhealth.43.20. PMID: 15732299. https://pubmed.ncbi.nlm.nih.gov/15732299/
  33. Roenneberg T, Allebrandt KV, Merrow M, Vetter C. Social jetlag and obesity. Curr Biol. 2012 May 22;22(10):939-43. doi: 10.1016/j.cub.2012.03.038. Epub 2012 May 10. Erratum in: Curr Biol. 2013 Apr 22;23(8):737. PMID: 22578422. https://pubmed.ncbi.nlm.nih.gov/22578422/
  34. Wong PM, Hasler BP, Kamarck TW, Muldoon MF, Manuck SB. Social Jetlag, Chronotype, and Cardiometabolic Risk. J Clin Endocrinol Metab. 2015 Dec;100(12):4612-20. doi: 10.1210/jc.2015-2923. Epub 2015 Nov 18. PMID: 26580236; PMCID: PMC4667156. https://pubmed.ncbi.nlm.nih.gov/26580236/
  35. Vitale JA, Weydahl A. Chronotype, Physical Activity, and Sport Performance: A Systematic Review. Sports Med. 2017 Sep;47(9):1859-1868. doi: 10.1007/s40279-017-0741-z. PMID: 28493061. https://pubmed.ncbi.nlm.nih.gov/28493061/
  36. Pengelly M, Elsworthy N, Guy J, Scanlan A, Lastella M. Player Chronotype Does Not Affect In-Game Performance during the Evening (>18:00 h) in Professional Male Basketball Players. Clocks Sleep. 2021 Nov 29;3(4):615-623. doi: 10.3390/clockssleep3040044. PMID: 34940023; PMCID: PMC8700237. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8700237/
  37. Myers, J., 2003. Exercise and cardiovascular health. Circulation, 107(1), pp.e2-e5. https://www.ahajournals.org/doi/abs/10.1161/01.cir.0000048890.59383.8d

Time-restricted Eating: 4 Critical Benefits for Health

time-restricted eating

By Jack Harley, MSc, University of Oxford 

We all know how important what we eat is for keeping healthy, but when you eat is also important. Time-restricted eating is a nutrition program that focuses on when you eat rather than what you eat. It involves limiting the period over which you eat during the day, and may help you consume fewer calories overall. 

What is time-restricted eating?

Time restricted eating is a nutrition program in which you restrict the timing of all your meals for the day within a 8-12 hour period. This leaves the remaining 12-16 hours of the day as a fasting period, in which no food is consumed.

People may adopt a time-restricted eating pattern for several reasons, such as to improve body composition, lose weight, sleep better or promote longevity

How to do time-restricted eating

Time-restricted eating is simple: choose a 8-12 hour window per day and eat all your meals within that period. If the goal is weight loss, the eating period should be less than your normal eating window. 

A popular method is the 16/8 method, in which you eat all of your meals of the day within an 8 hour period. This leaves a 16-hour fasting period each 24-hour cycle. For example, you could eat breakfast at 10 a.m., lunch at 2 p.m. and dinner at 6 p.m.. 

Alternatively, you could follow the 16/8 method by simply skipping breakfast and eating 2 or 3 meals between 12 noon and 8 p.m.. This similarly results in an 8-hour time-restricted eating pattern. 

It is not known what the ‘best’ time-restricted eating schedule is, as it is still a relatively new field of research. However, any 8-12 hour feeding period which is easy to maintain is probably most effective over the long-term.

Benefits of time-restricted eating

The many potential benefits of time-restricted include weight loss, improved cardiovascular health, and improved blood sugar levels. In addition, time-restricted eating may help to reset your circadian rhythm and help you live longer and healthier

Eating less

Most people consume calories from when they first wake up until they go to sleep at night. By limiting this ‘feeding’ window by following time-restricted eating, you may naturally eat less. 

In fact, some research has shown that time-restricted eating resulted in fewer calories being consumed overall. One study showed that men who followed a 10-hour time-restricted eating schedule consumed 20% fewer calories than those who ate freely. Another study showed that men who ate within a 4-hour period each day consumed 650 fewer calories per day than the control group. 

However, more research is needed to validate this finding, as other studies have demonstrated that time-restricted eating did not help to reduce the amount of calories consumed. One limitation of past research is that caloric intake is often estimated by dietary records which are self-reported, and may not always be accurate. 

Weight loss

Time-restricted eating may be effective in promoting weight loss, particularly in overweight or obese patients. 

Research by Dr. Satchin Panda from the Salk institute demonstrated that restricting food intake to a daily 8-hour window was associated with weight loss in obese patients. This 8-week long study showed that time-restricted eating resulted in a 3% reduction in body weight, compared to no change in body weight in the control group. Several other studies have also shown that time-restricted eating resulted in weight by 3% or more over a 1-month period. 

However, other studies have shown little to no weight loss from time-restricted eating, and so more research is needed. 

Therefore, the benefit of time-restricted eating for weight loss may depend on whether this eating pattern results in fewer calories being consumed. If you find that your daily energy intake per day is lower as a result of time-restricted eating, then it may be effective for weight loss. 

Cardiovascular health

The amount of ‘good’ (HDL) cholesterol and ‘bad’ (LDL) cholesterol in the blood can indicate your risk of heart disease. Research has shown that time-restricted eating may improve heart health by increasing ‘good’ cholesterol and lowering ‘bad’ cholesterol. 

One study found that 8-hour time restricted eating reduced levels of ‘bad’ cholesterol in the blood by 10% in 1 month. Other studies have shown that even 10-12 hour time-restricted eating can reduce ‘bad’ cholesterol levels by up to 35% over 1 month. 

However, other research has shown that a similar dietary pattern did not show a benefit to cholesterol levels. 

Metabolic health

Metabolism is the process by which the body converts food into energy. A time-restricted eating plan may improve metabolic health even if the total calories consumed remain the same. This is because time-restricted feeding may help to improve insulin sensitivity and blood sugar control. 

Some studies have shown time-restricted eating improved blood glucose and insulin response. This is important as it suggests that time-restricted feeding may help to reduce the risk of type 2 diabetes and other metabolic diseases.

One study showed that even when the total calories remained the same, eating within a 6-hour period was associated with decreased appetite and increased fat metabolism, compared to eating 3 meals across 12 hours. 

While time-restricted eating may help to improve blood glucose control and reduce markers of diabetes or pre-diabetes, more research is needed to validate this finding. 

Time-restricted eating and exercise

If you regularly exercise, you may be curious to know how time-restricted eating may influence weight loss and gains in strength and endurance. The available evidence suggests that the benefits of exercise are not reduced by a time-restricted eating schedule.

One 8-week trial showed that men following a time-restricted eating schedule gained just as much strength as those following a regular eating schedule. This suggests that time-restricted eating does not reduce strength improvements when following a workout program. 

Another 8-week study in men training showed that time-restricted eating resulted in a 15% loss of body fat compared to no fat loss in the control group who ate normally. In this study, both groups were performing weight training and saw similar improvements in strength and endurance. 

Time-restricted eating and longevity

Another benefit of time-restricted eating is that it may result in a longer and healthier life. In mice studies, micethat received one meal per day lived 11-14% longer than those that ate freely but consumed the same daily calories. This suggests that there is a metabolic benefit for longevity that is separate from simply restricting calories, which is known to extend lifespan in several animal species. However, more research is needed to verify whether the results of these animal studies will transfer to humans. 

Time-restricted eating and circadian rhythm

Circadian rhythm is the body’s 24-hour ‘biological clock’ that controls many important processes in the body. The most important of these is the sleep-wake cycle, which refers to the natural ebb and flow in sleepiness and awakeness during a 24-hour period. If you have ever experienced jet lag, you will be aware of the persistence of circadian rhythm. 

Following a time-restricted eating pattern may help to improve circadian rhythm. This is important for overall health, as a consistent circadian rhythm is important for getting high-quality, restorative sleep. 

How does circadian rhythm work?

Inside your cells and organs of the body are tiny biological ‘clocks’ that are synced to a master clock in the brain. This master clock responds to signals to tell the time, the most important being light. However, food is also a signal that the body uses to tell the time. For this reason, time-restricted eating may help to keep the biological clocks around the body synced to the ‘master’ clock in the brain.

Circadian rhythm and health

Circadian rhythms are closely tied to our body’s metabolism, and several metabolic processes such as appetite and energy expenditure occur in a cyclic way throughout a 24-hour cycle. 

When the circadian rhythm is disrupted, for example due to jet lag, shift work or irregular sleeping habits, this can negatively impact metabolism. However, eating within a consistent 8-12 hour period each day may help to ‘reset’ the biological clock and improve circadian rhythm.

A healthy circadian rhythm is important for getting proper sleep, and many cognitive functions such as learning and memory. On the other hand, an unhealthy circadian rhythm is associated with an increased risk of type 2 diabetes, mental illness and poor sleep

Therefore, research by Dr Satchin Panda at the Salk Institute and others demonstrating the benefit of time-restricted for maintaining circadian rhythm may be important for overall health.

What are other types of intermittent fasting?

Intermittent fasting is a broad term that describes nutrition programs that cycle between fasting and non-fasting periods. Time restricted eating is one type of intermittent fasting that follows a daily period of fasting. 

However, there are other types of intermittent fasting, which include: 

  • The 5:2 diet, in which you eat normally 5 days per week, but eat a reduced calorie diet on 2 days of the week
  • Eat Stop Eat diet, which involves one 24 hour fast each week.
  • Alternate-day fasting, in which you fast every second day. 



Time-restricted eating involves focusing on when you eat, rather than what you eat over a 24 hour period. By limiting food consumption to an 8-12 hour period, you may be able to lose weight by reducing calorie intake. In this way, time-restricted eating may help to combat weight gain and obesity. Even if you consume the same number of calories per day, you may still lose weight due to the beneficial effects of time-restricted feeding on metabolism. 

Some studies also suggest that time-restricted eating may improve heart health and blood sugar control. Additionally, time-restricted eating may also help to reset your circadian rhythm, resulting in better quality sleep. 

Time-restricted eating is a safe nutrition program, but always speak with your healthcare provider before altering your dietary practices. 


  1. Chow, L.S., Manoogian, E.N., Alvear, A., Fleischer, J.G., Thor, H., Dietsche, K., Wang, Q., Hodges, J.S., Esch, N., Malaeb, S. and Harindhanavudhi, T., 2020. Timerestricted eating effects on body composition and metabolic measures in humans who are overweight: a feasibility study. Obesity, 28(5), pp.860-869. https://onlinelibrary.wiley.com/doi/abs/10.1002/oby.22756
  2. Kesztyüs, D., Fuchs, M., Cermak, P. and Kesztyüs, T., 2020. Associations of time-restricted eating with health-related quality of life and sleep in adults: a secondary analysis of two pre-post pilot studies. BMC nutrition, 6(1), pp.1-8. https://bmcnutr.biomedcentral.com/articles/10.1186/s40795-020-00402-2
  3. Mitchell, S.J., Bernier, M., Mattison, J.A., Aon, M.A., Kaiser, T.A., Anson, R.M., Ikeno, Y., Anderson, R.M., Ingram, D.K. and de Cabo, R., 2019. Daily fasting improves health and survival in male mice independent of diet composition and calories. Cell Metabolism, 29(1), pp.221-228. https://linkinghub.elsevier.com/retrieve/pii/S1550413118305126
  4. Moro, T., Tinsley, G., Bianco, A., Marcolin, G., Pacelli, Q.F., Battaglia, G., Palma, A., Gentil, P., Neri, M. and Paoli, A., 2016. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. Journal of translational medicine, 14(1), pp.1-10. https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-016-1044-0?__s=ovzgowspzgzjrjm83r95
  5. Manoogian, E.N. and Panda, S., 2017. Circadian rhythms, time-restricted feeding, and healthy aging. Ageing research reviews, 39, pp.59-67. https://www.sciencedirect.com/science/article/pii/S1568163716303014
  6. Adlouni, A., Ghalim, N., Benslimane, A., Lecerf, J.M. and Saïle, R., 1997. Fasting during Ramadan induces a marked increase in high-density lipoprotein cholesterol and decrease in low-density lipoprotein cholesterol. Annals of nutrition and metabolism, 41(4), pp.242-249. https://pubmed.ncbi.nlm.nih.gov/9363296/
  7. Tinsley, G.M., Forsse, J.S., Butler, N.K., Paoli, A., Bane, A.A., La Bounty, P.M., Morgan, G.B. and Grandjean, P.W., 2017. Time-restricted feeding in young men performing resistance training: A randomized controlled trial. European journal of sport science, 17(2), pp.200-207. https://pubmed.ncbi.nlm.nih.gov/27550719/
  8. Liu, D., Huang, Y., Huang, C., Yang, S., Wei, X., Zhang, P., Guo, D., Lin, J., Xu, B., Li, C. and He, H., 2022. Calorie restriction with or without time-restricted eating in weight loss. New England Journal of Medicine, 386(16), pp.1495-1504. https://www.nejm.org/doi/full/10.1056/NEJMoa2114833
  9. Sawaya, A.L., Tucker, K., Tsay, R., Willett, W., Saltzman, E., Dallal, G.E. and Roberts, S.B., 1996. Evaluation of four methods for determining energy intake in young and older women: comparison with doubly labeled water measurements of total energy expenditure. The American journal of clinical nutrition, 63(4), pp.491-499. https://pubmed.ncbi.nlm.nih.gov/8599311/
  10. Gabel, K., Hoddy, K.K., Haggerty, N., Song, J., Kroeger, C.M., Trepanowski, J.F., Panda, S. and Varady, K.A., 2018. Effects of 8-hour time restricted feeding on body weight and metabolic disease risk factors in obese adults: A pilot study. Nutrition and healthy aging, 4(4), pp.345-353. https://content.iospress.com/articles/nutrition-and-healthy-aging/nha170036
  11. Aksungar, F.B., Topkaya, A.E. and Akyildiz, M., 2007. Interleukin-6, C-reactive protein and biochemical parameters during prolonged intermittent fasting. Annals of Nutrition and Metabolism, 51(1), pp.88-95. https://pubmed.ncbi.nlm.nih.gov/17374948/
  12. Aragon, A.A., Schoenfeld, B.J., Wildman, R., Kleiner, S., VanDusseldorp, T., Taylor, L., Earnest, C.P., Arciero, P.J., Wilborn, C., Kalman, D.S. and Stout, J.R., 2017. International society of sports nutrition position stand: diets and body composition. Journal of the International Society of Sports Nutrition, 14(1), p.16. https://pubmed.ncbi.nlm.nih.gov/28630601/
  13. Ma, H. and Shieh, K.J., 2006. Cholesterol and human health. The Journal of American Science, 2(1), pp.46-50. https://www.academia.edu/download/58425310/04-mahongbao.pdf
  14. Temizhan, A., Tandogan, I., Dönderici, Ö. and Demirbas, B., 2000. The effects of Ramadan fasting on blood lipid levels. The American journal of medicine, 109(4), p.341. https://pubmed.ncbi.nlm.nih.gov/11203145/
  15. Fakhrzadeh, H., Lariiani, B., Sanjari, M., Baradar-Jalili, R. and Amini, M.R., 2003. Effect of Ramadan fasting on clinical and biochemical parameters in healthy adults. Annals of Saudi medicine, 23(3-4), pp.223-226. https://pubmed.ncbi.nlm.nih.gov/16985327/
  16. Sutton, E.F., Beyl, R., Early, K.S., Cefalu, W.T., Ravussin, E. and Peterson, C.M., 2018. Early time-restricted feeding improves insulin sensitivity, blood pressure, and oxidative stress even without weight loss in men with prediabetes. Cell metabolism, 27(6), pp.1212-1221. https://linkinghub.elsevier.com/retrieve/pii/S1550413118302535
  17. Ravussin, E., Beyl, R.A., Poggiogalle, E., Hsia, D.S. and Peterson, C.M., 2019. Early time-restricted feeding reduces appetite and increases fat oxidation but does not affect energy expenditure in humans. Obesity, 27(8), pp.1244-1254. https://onlinelibrary.wiley.com/doi/abs/10.1002/oby.22518
  18. Tinsley, G.M., Forsse, J.S., Butler, N.K., Paoli, A., Bane, A.A., La Bounty, P.M., Morgan, G.B. and Grandjean, P.W., 2017. Time-restricted feeding in young men performing resistance training: A randomized controlled trial. European journal of sport science, 17(2), pp.200-207. https://pubmed.ncbi.nlm.nih.gov/27550719/
  19.  Moro, T., Tinsley, G., Bianco, A., Marcolin, G., Pacelli, Q.F., Battaglia, G., Palma, A., Gentil, P., Neri, M. and Paoli, A., 2016. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. Journal of translational medicine, 14(1), pp.1-10. https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-016-1044-0
  20. Mitchell, S.J., Bernier, M., Mattison, J.A., Aon, M.A., Kaiser, T.A., Anson, R.M., Ikeno, Y., Anderson, R.M., Ingram, D.K. and de Cabo, R., 2019. Daily fasting improves health and survival in male mice independent of diet composition and calories. Cell Metabolism, 29(1), pp.221-228. https://linkinghub.elsevier.com/retrieve/pii/S1550413118305126
  21. Everitt, A.V. and Le Couteur, D.G., 2007. Life extension by calorie restriction in humans. Annals of the New York Academy of Sciences, 1114(1), pp.428-433. https://nyaspubs.onlinelibrary.wiley.com/doi/abs/10.1196/annals.1396.005
  22. Manoogian, E.N., Chow, L.S., Taub, P.R., Laferrère, B. and Panda, S., 2022. Time-restricted eating for the prevention and management of metabolic diseases. Endocrine reviews, 43(2), pp.405-436. https://academic.oup.com/edrv/article-abstract/43/2/405/6371193
  23. Pevet, P. and Challet, E., 2011. Melatonin: both master clock output and internal time-giver in the circadian clocks network. Journal of Physiology-Paris, 105(4-6), pp.170-182. https://www.sciencedirect.com/science/article/abs/pii/S0928425711000040
  24. Huang, W., Ramsey, K.M., Marcheva, B. and Bass, J., 2011. Circadian rhythms, sleep, and metabolism. The Journal of clinical investigation, 121(6), pp.2133-2141. https://www.academia.edu/download/67026203/a9c42734900eaba817a88fb62cd169a200e5.pdf
  25. Huang, W., Ramsey, K.M., Marcheva, B. and Bass, J., 2011. Circadian rhythms, sleep, and metabolism. The Journal of clinical investigation, 121(6), pp.2133-2141. https://www.jci.org/articles/view/46043
  26. Chaix, A., Manoogian, E.N., Melkani, G.C. and Panda, S., 2019. Time-restricted eating to prevent and manage chronic metabolic diseases. Annual review of nutrition, 39, p.291. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6703924/        
  27. Longo, V.D. and Panda, S., 2016. Fasting, circadian rhythms, and time-restricted feeding in healthy lifespan. Cell metabolism, 23(6), pp.1048-1059. https://www.sciencedirect.com/science/article/pii/S1550413116302509
  28. Mason, I.C., Qian, J., Adler, G.K. and Scheer, F.A., 2020. Impact of circadian disruption on glucose metabolism: implications for type 2 diabetes. Diabetologia, 63(3), pp.462-472. https://link.springer.com/article/10.1007/s00125-019-05059-6
  29. Foster, R.G., Peirson, S.N., Wulff, K., Winnebeck, E., Vetter, C. and Roenneberg, T., 2013. Sleep and circadian rhythm disruption in social jetlag and mental illness. Progress in molecular biology and translational science, 119, pp.325-346. https://www.sciencedirect.com/science/article/abs/pii/B9780123969712000117
  30. Phillips, N.E., Mareschal, J., Schwab, N., Manoogian, E.N., Borloz, S., Ostinelli, G., Gauthier-Jaques, A., Umwali, S., Gonzalez Rodriguez, E., Aeberli, D. and Hans, D., 2021. The effects of time-restricted eating versus standard dietary advice on weight, metabolic health and the consumption of processed food: a pragmatic randomised controlled trial in community-based adults. Nutrients, 13(3), p.1042. https://www.mdpi.com/1045770
  31. Varady, K.A., Cienfuegos, S., Ezpeleta, M. and Gabel, K., 2021. Cardiometabolic benefits of intermittent fasting. Annual Review of Nutrition, 41, pp.333-361. https://www.annualreviews.org/doi/abs/10.1146/annurev-nutr-052020-041327

Sleep: Quality, 5 Phases, Circadian Rhythm, Disorders

sleep circadian

By Jack Harley, MSc, University of Oxford 

When thinking about how much sleep we need, it’s common to focus on the number of hours of sleep we get. But while total sleep duration is important, it’s not the full story – the quality of our sleep also matters.

To understand sleep quality, it’s important to understand that sleep is not a uniform process. Rather, your brain and body go through several sleep cycles during the night, each cycle consisting of 5 unique stages. Each stage of sleep helps to ensure the mind and body wake up feeling refreshed.

Understanding the sleep stages can explain how certain sleep disorders such as insomnia may arise, and how you can improve your sleep.


What is the sleep cycle?

During the night, the brain and body progresses through a series of sleep cycles. Sleep cycles typically last between 90 minutes to two hours, and during this time the brain progresses through five phases:

Sleep stage Type of sleep Alternative names Typical length
Stage 1 non-REM  N1, light sleep 5-10 minutes
Stage 2 non-REM  N2, light sleep 10-60 minutes
Stages 3 and 4 non-REM  N3, slow-wave sleep, delta sleep 20-40 minutes
Stage 5 REM  REM sleep 10-60 minutes

A person will generally go through between 4 to 6 sleep cycles in a normal night of sleep lasting 7 to 9 hours. Sleep cycles vary from person to person and are influenced by a variety of factors such as age, alcohol consumption, and recent sleep patterns. During the night, you spend different amounts of time in each phase of sleep, and this changes in each sleep cycle. 

What are the stages of sleep?

There are 5 stages of sleep, 1 that involves rapid eye movement (REM), called REM sleep, and 4 that do not, known as non-REM (NREM) sleep. These stages are primarily determined by the recorded brain activity, which is distinct for each stage. The stages are listed below: 

Stage 1

The first stage of sleep is a non-REM sleep known as light sleep. This is essentially the ‘dozing off’ stage, as your eyes are closed but you may be easily awoken. During this stage, activity in the brain and body begins to decline, but the body has not yet fully relaxed

This stage typically lasts 5-10 minutes, and if the person is not woken up, they will quickly move into stage 2 sleep. During the rest of the night, the person will generally not spend any more time in stage 1 as they move into further sleep cycles. 

Stage 2

During the second stage of non-REM sleep, still considered light sleep, further relaxation occurs. The muscles relax, body temperature decreases, and breathing and heart rate slow. At the same time, eye movement stops and the brain shows a new pattern of activity

Brain activity slows down, although the EEG charts show short spikes of activity that actually prevent you from being easily woken up. These bursts of brain wave activity are also thought to also play a role in long-term memory consolidation

Stage 2 sleep lasts between 10 and 25 minutes during the first sleep cycle, becoming longer after each sleep cycle. During a night of sleep, the average person spends about 50% of their overall sleep time in stage 2. 

Stage 3 and 4

Stage 3 and 4 are known as deep sleep, and it is much harder to wake up someone if they are  in these stages. 

During these phases, muscles relax even further, and pulse and breathing slow. The brain produces a characteristic pattern called delta waves, which is why this phase is sometimes called delta sleep or slow-wave sleep (SWS)

This phase of sleep is thought to play an important role in mental and physical recovery, as well as growth. Even though brain activity has slowed down, this stage of sleep contributes to creativity and memory

Most of the time we spend in deep sleep occurs in the first half of the night. During the early sleep cycles, deep sleep typically lasts 20-40 minutes. Later in the night, this type of sleep becomes shorter as you spend more time in REM sleep

Stage 5 

During stage 5, or REM sleep, brain activity increases to similar levels as seen during the day, and this is the phase of sleep in which dreams occur most frequently. 

During REM sleep, the muscles of the body experience a temporary paralysis known as atonia, with the exception of the eyes and breathing muscles. Although the eyes are closed, they move around rapidly, which is where the name ‘rapid eye movement’ (REM) sleep comes from. 

During REM sleep, heart rate and blood pressure increase, while breathing can become fast and shallow during this stage. REM sleep is believed to play an important role in cognitive functions such as memory and learning

You won’t normally enter REM sleep until you have been sleeping for at least 90 minutes. As you progress through each sleep cycle, the amount of time spent in REM sleep increases

While you may only spend a few minutes in REM sleep during the first sleep cycle, this may increase to an hour spent in REM in later cycles. Overall, adults spend roughly 25% of their total sleep time in REM sleep. As we age, the amount of time we spend in REM sleep tends to decline


Why do sleep stages matter?

The accumulation of time in each of the 5 stages of sleep is known as sleep architecture, and is important for allowing the brain and body to recover and grow. Regularly getting too little sleep, or not enough time in stage 3 to 5 may negatively impact important brain functions such as cognition, emotional processing and physical health. Sleep deprivation may also increase the risk of several health conditions such as type 2 diabetes and heart disease.

What affects the time spent in each sleep stage?

Several factors have been shown through research studies to impact sleep architecture, the amount of time spent in the 5 stages of sleep. These include: 

  • Age greatly affects the time spent in the stages of sleep. While newborns may spend around 50% of their total sleep time in REM sleep and enter this stage quickly, older adults may spend only 20% of the time in this stage.
  • Alcohol can reduce the amount of REM sleep early in the night. However, as the alcohol wears off, REM sleep rebound occurs resulting in more REM sleep later on. 
  • Sleep disorders such as obstructive sleep apnea or restless leg syndrome may cause you to frequently wake during the night, preventing you from getting enough deep and REM sleep. 
  • Recent sleep/wake cycles in previous days or weeks can affect the time spent in each stage of sleep during the night. 

Sleep disorders

Sleep disorders are a group of conditions that affect a person’s ability to regularly get high-quality sleep. While it is fairly normal to occasionally have a poor sleep, when this begins to occur on a regular basis it may indicate a sleep disorder. 

Types of sleep disorders include: 

  • Insomnia: is an inability to fall asleep easily or remain asleep during the night. Insomnia is a very common condition, experienced by up to 50% of people in the United States at some point in their lives.
  • Sleep apnea: involves temporary pauses in breathing during sleep. This may cause the person to wake up, or receive insufficient oxygen during the night. There are two types: obstructive sleep apnea, in which the airways are physically blocked, and central sleep apnea, in which the connection between the brain and the breathing muscles is not functioning properly.

What are the symptoms of sleep disorders?

Common symptoms of sleep disorders include: 

  • Fatigue during the day
  • Difficulty falling or staying asleep
  • Irritability
  • Anxiety
  • Difficulty concentrating
  • Weight gain

If you regularly experience one or more of the above, it is recommended that you consult your healthcare practitioner. 

How are sleep disorders diagnosed and treated?

To diagnose a sleep disorder, your doctor will generally perform a physical examination and take a medical history, and may request that a sleep study be conducted. Treatments for sleep disorders include pharmaceuticals or lifestyle changes, such as: 

  • Melatonin supplements
  • Sleeping pills
  • Exercise
  • Stress reduction
  • Limiting caffeine during the day
  • Reducing tobacco and alcohol consumption
  • Following a regular sleep schedule

Sleep and circadian rhythm

Just as our sleep follows a cycle, so too does our wakefulness and our transition from wakefulness to sleep. The 24-hour cycle that makes us feel sleepy at night and awake during the day is known as circadian rhythm, and is built into our biology.

Circadian rhythms control many physical and mental processes such as:

  • Sleep-wake cycle
  • Body temperature
  • Hormone levels 
  • Alertness and drowsiness

How does circadian rhythm work?

Different systems of the body follow circadian rhythms that are synchronized with a master clock in the brain. This master clock responds to a range of environmental signals to inform the body to sleep or be awake. Light is the most important signal for circadian rhythm, which is why exposure to bright lights from electronic screens at nighttime can alter our circadian rhythm. 

If we often feel tired during the day or awake at night, we may be experiencing a circadian rhythm sleep disorder.

What are circadian rhythm sleep disorders?

Circadian rhythm sleep disorders are a group of sleep disorders in which the circadian clock is altered. The most common types of circadian rhythm sleep disorders include: 

Delayed sleep phase syndrome (DSPS): you sleep and wake more than 2 hours later than what is typically considered a normal sleep-wake cycle. For example, you regularly go to sleep at 2 a.m. or later. People with this condition are often most alert and awake at nighttime, and it is most common in young adults

Advanced sleep phase syndrome (ASPS): causes you to go to sleep earlier than you want to (6 p.m. to 9 p.m.), and wake up in the early morning (2 a.m. to 5 a.m.). This condition is most common amongst older adults

Jet lag: your body’s circadian rhythm is synced to a different time zone. The sleep/wake cycle makes it hard to align your sleeping and waking times to the new environment. Jet lag can occur due to long flights, or changing time zones during travel. 


Shift work disorder: shift work may put your body’s circadian rhythm at odds with daylight hours. This may result in you getting up to 4 hours less sleep than the average person, as well as poor sleep quality.

What are the symptoms of circadian rhythm disorders?

Circadian rhythm disorders result in altered sleep onset, and often poor sleep, or daytime sleepiness. The most common symptoms include: 

  • Insomnia 
  • Daytime sleepiness
  • Stress
  • Reduced ability to focus
  • Sleep loss
  • Difficulty waking up

What causes circadian rhythm sleep disorders?

Circadian rhythm sleep disorders are caused by frequent disturbances in the circadian cycle, resulting in a disruption to the brain’s regulation of the sleep-wake cycle. In some cases, there may be a mismatch between the internal body clock and the external environment. 

Circadian rhythm sleep disorders may be caused by

  • Frequent changes in sleeping and waking times
  • Brain injuries such as stroke and dementia
  • Older age
  • Shift work
  • Jet lag

What is the diagnosis and treatment of circadian rhythm disorders?

To diagnose a circadian rhythm sleep disorder, your doctor will perform a physical examination, take a medical history, and may request for a sleep study to be performed. Treatment for circadian rhythm sleep disorders may include supplements or medications such as: 

  • Melatonin
  • Benzodiazepines such as Xanax
  • Nonbenzodiazepine hypnotics such as Ambien

Other lifestyle changes that may be prescribed to improve circadian rhythm include:

  • Avoiding eating a meal too close to bedtime
  • Exposure to bright lights (e.g. daylight) in the morning
  • Following a time-restricted eating schedule in which all food is consumed within an 8-12 hour period
  • Going to sleep and waking up at the same times each day
  • Eating breakfast at the same time each day

The above lifestyle recommendations have been proposed by Dr Satchin Panda of the Salk Institute and other circadian rhythm experts to improve circadian rhythm. 


Understanding the stages of sleep may help you to avoid sleep problems and excessive daytime sleepiness. Sleep occurs in cycles made up of five stages. Sleep disruption, especially during the deep sleep and REM stages, may result in poor sleep quality. 

To avoid sleep disturbance and short sleep duration, it is important to keep your circadian rhythm running in a healthy way. This will ensure you are not at an increased risk of a sleep disorder, including a circadian rhythm disorder. 



  1.  Carskadon, M.A. and Dement, W.C., 2005. Normal human sleep: an overview. Principles and practice of sleep medicine, 4(1), pp.13-23. http://apsychoserver.psych.arizona.edu/jjbareprints/psyc501a/readings/Carskadon%20Dement%202011.pdf
  2. Reinoso-Suárez, F., Andrés, I.D. and Garzón, M., 2011. The Sleep–Wakefulness Cycle. Functional Anatomy of the Sleep-Wakefulness Cycle: Wakefulness, pp.1-4. https://link.springer.com/chapter/10.1007/978-3-642-14626-8_1
  3. Steyn-Ross, D.A., Steyn-Ross, M.L., Sleigh, J.W., Wilson, M.T., Gillies, I.P. and Wright, J.J., 2005. The sleep cycle modelled as a cortical phase transition. Journal of Biological Physics, 31(3), pp.547-569. https://link.springer.com/article/10.1007/s10867-005-1285-2
  4. Shochat, T., Cohen-Zion, M. and Tzischinsky, O., 2014. Functional consequences of inadequate sleep in adolescents: a systematic review. Sleep medicine reviews, 18(1), pp.75-87. https://www.sciencedirect.com/science/article/abs/pii/S1087079213000440
  5. Carskadon, M.A. and Rechtschaffen, A., 2011. Monitoring and staging human sleep. Principles and practice of sleep medicine, 5, pp.16-26. http://apsychoserver.psych.arizona.edu/JJBAReprints/PSYC501A/Readings/Hirshkowitz_Monitoring%20and%20Staging%20Human%20Sleep.pdf
  6. Bush, B. and Hudson, T., 2010. The role of cortisol in sleep. Natural Medicine Journal, 2(6), pp.2010-06. https://www.naturalmedicinejournal.com/journal/role-cortisol-sleep
  7. Brown, E.N., Lydic, R. and Schiff, N.D., 2010. General anesthesia, sleep, and coma. New England Journal of Medicine, 363(27), pp.2638-2650. https://www.nejm.org/doi/full/10.1056/Nejmra0808281
  8. Aboalayon, K.A.I., Faezipour, M., Almuhammadi, W.S. and Moslehpour, S., 2016. Sleep stage classification using EEG signal analysis: a comprehensive survey and new investigation. Entropy, 18(9), p.272. https://www.mdpi.com/153006
  9. Lambert, I., TramoniNegre, E., Lagarde, S., Roehri, N., Giusiano, B., TrebuchonDa Fonseca, A., Carron, R., Benar, C.G., Felician, O. and Bartolomei, F., 2020. Hippocampal interictal spikes during sleep impact longterm memory consolidation. Annals of Neurology, 87(6), pp.976-987. https://onlinelibrary.wiley.com/doi/abs/10.1002/ana.25744
  10. Patel, A.K., Reddy, V. and Araujo, J.F., 2021. Physiology, sleep stages. In StatPearls [Internet]. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK526132/
  11. Born, J., 2010. Slow-wave sleep and the consolidation of long-term memory. The World Journal of Biological Psychiatry, 11(sup1), pp.16-21. https://www.tandfonline.com/doi/abs/10.3109/15622971003637637
  12. Fatt, S.J., Beilharz, J.E., Joubert, M., Wilson, C., Lloyd, A.R., Vollmer-Conna, U. and Cvejic, E., 2020. Parasympathetic activity is reduced during slow-wave sleep, but not resting wakefulness, in patients with chronic fatigue syndrome. Journal of Clinical Sleep Medicine, 16(1), pp.19-28. https://jcsm.aasm.org/doi/abs/10.5664/jcsm.8114
  13. Landmann, N., Kuhn, M., Piosczyk, H., Feige, B., Baglioni, C., Spiegelhalder, K., Frase, L., Riemann, D., Sterr, A. and Nissen, C., 2014. The reorganisation of memory during sleep. Sleep medicine reviews, 18(6), pp.531-541. https://www.sciencedirect.com/science/article/pii/S1087079214000264
  14. Palagini, L., Baglioni, C., Ciapparelli, A., Gemignani, A. and Riemann, D., 2013. REM sleep dysregulation in depression: state of the art. Sleep medicine reviews, 17(5), pp.377-390. https://www.sciencedirect.com/science/article/pii/S1087079212001207
  15. Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. Stages of Sleep. Available from: https://www.ncbi.nlm.nih.gov/books/NBK10996/
  16. McCarter, S.J., St Louis, E.K. and Boeve, B.F., 2012. REM sleep behavior disorder and REM sleep without atonia as an early manifestation of degenerative neurological disease. Current neurology and neuroscience reports, 12(2), pp.182-192. https://link.springer.com/article/10.1007/s11910-012-0253-z
  17. Roth, T., 2004. Characteristics and determinants of normal sleep. J Clin Psychiatry, 65(Suppl 16), pp.8-11. https://www.psychiatrist.com/wp-content/uploads/2021/02/11523_characteristics-determinants-normal-sleep.pdf
  18. Bušek, P., Vaňková, J., Opavský, J., Salinger, J. and Nevšímalová, S., 2005. Spectral analysis of heart rate variability in sleep. Physiol res, 54(4), pp.369-376. https://www.researchgate.net/profile/Jiri-Salinger/publication/8140194_Spectral_analysis_of_heart_rate_variability_in_sleep/links/53f6fc320cf2888a74975dd6/Spectral-analysis-of-heart-rate-variability-in-sleep.pdf
  19. Siegel, J.M., 2001. The REM sleep-memory consolidation hypothesis. Science, 294(5544), pp.1058-1063. https://www.science.org/doi/abs/10.1126/science.1063049
  20. Colten, H.R. and Altevogt, B.M., 2006. Sleep physiology. In Sleep disorders and sleep deprivation: An unmet public health problem. National Academies Press (US). https://www.ncbi.nlm.nih.gov/books/NBK19956
  21. Shrivastava, D., Jung, S., Saadat, M., Sirohi, R. and Crewson, K., 2014. How to interpret the results of a sleep study. Journal of community hospital internal medicine perspectives, 4(5), p.24983.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4246141/
  22. Van Cauter, E., Leproult, R. and Plat, L., 2000. Age-related changes in slow wave sleep and REM sleep and relationship with growth hormone and cortisol levels in healthy men. Jama, 284(7), pp.861-868.  https://jamanetwork.com/journals/jama/article-abstract/192981
  23. Parcell, D.L., Ponsford, J.L., Redman, J.R. and Rajaratnam, S.M., 2008. Poor sleep quality and changes in objectively recorded sleep after traumatic brain injury: a preliminary study. Archives of physical medicine and rehabilitation, 89(5), pp.843-850. https://www.sciencedirect.com/science/article/abs/pii/S0003999308001056
  24. Killgore, W.D., 2010. Effects of sleep deprivation on cognition. Progress in brain research, 185, pp.105-129. https://www.sciencedirect.com/science/article/pii/B9780444537027000075
  25. Spiegel, K., Knutson, K., Leproult, R., Tasali, E. and Van Cauter, E., 2005. Sleep loss: a novel risk factor for insulin resistance and Type 2 diabetes. Journal of applied physiology. https://journals.physiology.org/doi/full/10.1152/japplphysiol.00660.2005?view=long&pmid=16227462
  26. Yuan, R., Wang, J. and Guo, L.L., 2016. The effect of sleep deprivation on coronary heart disease. Chinese Medical Sciences Journal, 31(4), pp.247-253. https://www.sciencedirect.com/science/article/abs/pii/S1001929417300081
  27. Ebrahim, I.O., Shapiro, C.M., Williams, A.J. and Fenwick, P.B., 2013. Alcohol and sleep I: effects on normal sleep. Alcoholism: Clinical and Experimental Research, 37(4), pp.539-549. https://onlinelibrary.wiley.com/doi/abs/10.1111/acer.12006
  28. Olaithe, M., Bucks, R.S., Hillman, D.R. and Eastwood, P.R., 2018. Cognitive deficits in obstructive sleep apnea: insights from a meta-review and comparison with deficits observed in COPD, insomnia, and sleep deprivation. Sleep medicine reviews, 38, pp.39-49. https://www.sciencedirect.com/science/article/pii/S1087079217300709
  29. Bhaskar, S., Hemavathy, D. and Prasad, S., 2016. Prevalence of chronic insomnia in adult patients and its correlation with medical comorbidities. Journal of family medicine and primary care, 5(4), p.780. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5353813/
  30. Cortese, S., Konofal, E., Lecendreux, M., Arnulf, I., Mouren, M.C., Darra, F. and Bernardina, B.D., 2005. Restless legs syndrome and attention-deficit/hyperactivity disorder: a review of the literature. Sleep, 28(8), pp.1007-1013. https://academic.oup.com/sleep/article-abstract/28/8/1007/2708104
  31. Javaheri, S., Barbe, F., Campos-Rodriguez, F., Dempsey, J.A., Khayat, R., Javaheri, S., Malhotra, A., Martinez-Garcia, M.A., Mehra, R., Pack, A.I. and Polotsky, V.Y., 2017. Sleep apnea: types, mechanisms, and clinical cardiovascular consequences. Journal of the American College of Cardiology, 69(7), pp.841-858. https://www.jacc.org/doi/abs/10.1016/j.jacc.2016.11.069
  32. Hombali, A., Seow, E., Yuan, Q., Chang, S.H.S., Satghare, P., Kumar, S., Verma, S.K., Mok, Y.M., Chong, S.A. and Subramaniam, M., 2019. Prevalence and correlates of sleep disorder symptoms in psychiatric disorders. Psychiatry research, 279, pp.116-122. https://www.sciencedirect.com/science/article/pii/S0165178118302683
  33. Chervin, R.D., Dillon, J.E., Bassetti, C., Ganoczy, D.A. and Pituch, K.J., 1997. Symptoms of sleep disorders, inattention, and hyperactivity in children. Sleep, 20(12), pp.1185-1192. https://academic.oup.com/sleep/article-abstract/20/12/1185/2750014
  34. McDonagh, M.S., Holmes, R. and Hsu, F., 2019. Pharmacologic treatments for sleep disorders in children: A systematic review. Journal of child neurology, 34(5), pp.237-247. https://journals.sagepub.com/doi/abs/10.1177/0883073818821030
  35. Panda, S., Hogenesch, J.B. and Kay, S.A., 2002. Circadian rhythms from flies to human. Nature, 417(6886), pp.329-335. https://www.nature.com/articles/417329a
  36. Sulli, G., Manoogian, E.N., Taub, P.R. and Panda, S., 2018. Training the circadian clock, clocking the drugs, and drugging the clock to prevent, manage, and treat chronic diseases. Trends in pharmacological sciences, 39(9), pp.812-827. https://www.sciencedirect.com/science/article/pii/S0165614718301196
  37. Panda, S. and Hogenesch, J.B., 2004. It’s all in the timing: many clocks, many outputs. Journal of biological rhythms, 19(5), pp.374-387. https://journals.sagepub.com/doi/abs/10.1177/0748730404269008
  38. Danielsson, K., Markström, A., Broman, J.E., von Knorring, L. and Jansson-Fröjmark, M., 2016. Delayed sleep phase disorder in a Swedish cohort of adolescents and young adults: prevalence and associated factors. Chronobiology international, 33(10), pp.1331-1339. https://www.tandfonline.com/doi/abs/10.1080/07420528.2016.1217002
  39. Guidozzi, F., 2015. Gender differences in sleep in older men and women. Climacteric, 18(5), pp.715-721. https://www.tandfonline.com/doi/abs/10.3109/13697137.2015.1042451
  40. McDowall, K., Murphy, E. and Anderson, K., 2017. The impact of shift work on sleep quality among nurses. Occupational Medicine, 67(8), pp.621-625. https://academic.oup.com/occmed/article-abstract/67/8/621/4430301
  41. Walker, W.H., Walton, J.C., DeVries, A.C. and Nelson, R.J., 2020. Circadian rhythm disruption and mental health. Translational psychiatry, 10(1), pp.1-13. https://www.nature.com/articles/s41398-020-0694-0
  42. Stevanovic, K., Yunus, A., Joly-Amado, A., Gordon, M., Morgan, D., Gulick, D. and Gamsby, J., 2017. Disruption of normal circadian clock function in a mouse model of tauopathy. Experimental neurology, 294, pp.58-67. https://www.sciencedirect.com/science/article/pii/S0014488617301085
  43. Drake, C.L., 2010. The characterization and pathology of circadian rhythm sleep disorders. Journal of Family Practice, 59(1), pp.S12-S12. https://go.gale.com/ps/i.do?id=GALE%7CA218120439&sid=googleScholar&v=2.1&it=r&linkaccess=abs&issn=00943509&p=AONE&sw=w
  44. Morgenthaler, T.I., Lee-Chiong, T., Alessi, C., Friedman, L., Aurora, R.N., Boehlecke, B., Brown, T., Chesson Jr, A.L., Kapur, V., Maganti, R. and Owens, J., 2007. Practice parameters for the clinical evaluation and treatment of circadian rhythm sleep disorders. Sleep, 30(11), pp.1445-1459. https://academic.oup.com/sleep/article-abstract/30/11/1445/2696876
  45. Roepke, S.K. and Ancoli-Israel, S., 2010. Sleep disorders in the elderly. Indian Journal of Medical Research, 131(2), p.302. https://www.researchgate.net/profile/Sonia-Ancoli-Israel/publication/42389740_Sleep_disorders_in_the_elderly/links/09e415069aeeee633c000000/Sleep-disorders-in-the-elderly.pdf
  46. Sulli, G., Manoogian, E.N., Taub, P.R. and Panda, S., 2018. Training the circadian clock, clocking the drugs, and drugging the clock to prevent, manage, and treat chronic diseases. Trends in pharmacological sciences, 39(9), pp.812-827. https://www.sciencedirect.com/science/article/abs/pii/S0165614718301196

6 New Daily Habits For Optimal Circadian Rhythm

circadian rhythm

By Jack Harley, MSc, University of Oxford 

We all know getting quality sleep is important, but it’s not the full story. It is possible to get 8 hours of sleep, and still feel groggy in the morning. In this case, you may have neglected to take care of your circadian rhythm. Fortunately, you can get your circadian rhythm back on track by following a few simple daily habits.

What is circadian rhythm? 

Circadian rhythm refers to the body’s internal processes that maintain the sleep-wake cycle. They encompass physical and psychological changes that occur over a 24-hour period. Circadian rhythms cause our bodies to be active during the day, and restful at night. If you have ever had jet lag, you will know how persistent circadian rhythms can be. 

As well as controlling the sleep/wake cycle, circadian rhythm also influences a range of other biological factors such:

  • Arousal and drowsiness
  • Metabolism
  • Energy levels
  • Stress hormone levels 
  • Health and risk of disease

How does circadian rhythm work?

Inside every cell in the body are molecular clocks that tick away in an established rhythm. These internal clocks are synchronized by a master clock in a part of the brain called the suprachiasmatic nucleus (SCN). 

This clock responds to environmental signals to tell the time, the most important of which is light. When light enters our eyes, it signals to the master clock that it is day or night. In the morning, this light results in the body producing cortisol, making us feel alert and awake. At night, the pineal gland produces melatonin, which reduces wakefulness and makes us feel sleepy. 

The master clock is also influenced by other environmental cues such as food intake, movement, exercise and temperature. 

Why is circadian rhythm important? 

Circadian rhythm is essential for health and wellbeing. It is also important for feeling focused and energized during the day. If you often experience daytime sleepiness, or difficulty falling asleep at night, it may be a sign that your circadian rhythm is off. 

A misaligned circadian rhythm over a long period of time may be associated with a range of health conditions such as:

A poor circadian rhythm is also linked to psychiatric conditions such as depression and bipolar disorder, as well as neurodegenerative diseases like dementia.

However, a properly aligned circadian rhythm is associated with improved sleep quality and reduced risk of adverse health effects. Circadian rhythm is also associated with improved measures of cognitive function including attention, learning ability, and working memory. This may result in higher productivity during the day. 

What factors affect circadian rhythm? 

Circadian rhythms can be altered by many common aspects of our modern lifestyle.

For example, if we go to bed at 10 pm one day, and 2 am the next, our internal body clocks become confused. This can make it harder to fall asleep, reducing the quality of our sleep and throwing off our circadian rhythm. 

Several environmental cues, known as ‘zeitgebers’, can influence our circadian rhythm. These include: 

  • Sleep timing and duration
  • Light exposure
  • Food consumption and timing
  • Movement and exercise
  • Temperature 

Unfortunately, many common habits and routines may disrupt our circadian rhythm. These include: 

  • Shift work
  • Eating late at night
  • Exposure to bright lights at night, for example from a phone or laptop
  • Changing time zones when flying to another country 
  • Sleeping at different times each day

Fortunately, it is often possible to restore a healthy circadian rhythm by following a few simple daily habits.

The ideal circadian day

In a perfect world, you would go to bed when it is dark and wake up when the sun rises, so your sleeping pattern would match that of the sun. This would ensure an optimal circadian rhythm. 

However, due to work, family and other obligations, it is often hard to follow the ‘early sleep, early wake’ philosophy. Even so, we can still establish a realistic circadian day that is compatible with our daily schedule, by following six daily habits listed below. 

1. Go to bed at a consistent time

In order to maintain a healthy circadian rhythm, it is important to follow a regular sleep schedule. Sleeping at the same time each night and getting consistent amounts of sleep can help establish this habit.

You should go to sleep at a time that allows you to get the recommended amount of sleep, which is 7 hours for most adults. For example, if you need to wake up at 7 a.m. for work, you should be in bed ready to sleep at 12 a.m. 

Try to choose a sleep schedule that you can maintain every day, including weekends and holidays. Sleeping in on weekends may be tempting, but doing so may disrupt your circadian rhythm and make it difficult to get back to a consistent routine. 

It is also important to wake up at the same time every day. However, if you go to sleep at the same time and sleep for a consistent duration, this should happen automatically. 

2. Wait at least 1 hour after waking up before eating 

Try to avoid eating as soon as you wake up, and instead. Instead, wait at least 1 hour before eating your first meal. This will extend the overnight period of fasting, allowing your circadian rhythm to reset. 

Waiting 1 hour or more to eat breakfast can also make it easier to follow a time-restricted eating pattern. Time-restricted eating involves consuming all of the food for the day within a period of between 12 to 16 hours. This fasting period helps to improve your circadian rhythm, and may also promote weight loss, help treat type 2 diabetes and improve metabolic function.

3. Eat breakfast at a consistent time

The timing of breakfast can send a signal to the body’s internal clock about the time of day. Changing the time you eat your first meal regularly can confuse the body’s internal clock and disrupt the circadian rhythm

Therefore, try and eat breakfast at a similar time each day. For example, if you wake up at 7 a.m., you may wish to eat breakfast at 8 a.m. or 8.30 a.m. daily. 

4. Eat your last meal 2-3 hours before bed

Try to leave at least 2-3 hours between when you eat your last mouthful of food and when you intend to sleep. Eating too close to bedtime can disturb the quality of your sleep, and disrupt your circadian rhythm

In addition, eating your last meal at least 2-3 hours before bed makes it easier to follow a time-restricted eating schedule, which helps to maintain a healthy circadian rhythm.

While you are avoiding food in the late evening, try to also avoid exposure to bright lights. Light, particularly blue lights emitted from electronic devices may signal our circadian rhythm that it is daytime. Try to avoid using a phone or laptop too close to bedtime, and dim the lights to help prepare your mind for sleep. 

5. Get at least 30 minutes of bright light during the day

Light is the most important trigger for circadian rhythm. Therefore, try and go outside for at least 30 minutes in the morning and expose yourself to daylight. Doing so sends a signal to the brain that it is time to wake up and helps to reset your circadian clock. 

It is important to go outdoors if possible, as the amount of sunlight outside is vastly more than that inside, even when the lights are switched on. On a cloudy day, you may receive more than 100,000 lux (a measurement unit of light) outdoors, compared to only 100 lux indoors. 

To expose yourself to bright lights in the morning, you could try the following: 

  • Eating your breakfast or drink coffee outside, e.g. on your front porch
  • Eating your breakfast near a well-lit window
  • Riding a bicycle to work instead of driving
  • Going for a walk or run in the morning 

Alternatively, if none of the above are convenient, you can buy a special light box that emits blue light and use it to increase your morning light exposure.

6. Exercise for at least 30 minutes per day

Exercise and sleep support each other in a mutually beneficial way. Regular exercise promotes deeper and more restorative sleep, which in turn allows for more energy the following day to exercise. Both of these factors help to establish a healthy circadian rhythm

However, it is best to avoid exercising 1-2 hours before bedtime, as this can make it harder to fall asleep. If possible, try to exercise outdoors during the day to receive additional sunlight and further improve circadian rhythm. 

Putting it all together

Combining the above habits, a circadian day might look like this:

  • At 7 a.m, you wake up, go outside for a brisk 30 minute walk, and then eat breakfast at 8 a.m.
  • You head to work, and eat lunch at 1 p.m. 
  • You arrive home and eat dinner, your last meal of the day, at 7.pm. 
  • From 9 p.m. until 11 p.m., avoid snacking or checking your phone or laptop, before sleeping at 12 a.m.

The above schedule is only a suggestion, and you may need to adjust it to fit your personal schedule.


Circadian rhythm can be thought of as an energy schedule, with peaks and dips during the day. 

When your circadian rhythm is out of sync, you may feel tired during the day or struggle to sleep at night. On the other hand, maintaining a healthy circadian rhythm can leave you feeling energetic and focused during the day, and sleepy at night. By following a few simple daily habits, you can take steps to improve your circadian rhythm. 



  1.  Sulli, G., Manoogian, E.N., Taub, P.R. and Panda, S., 2018. Training the circadian clock, clocking the drugs, and drugging the clock to prevent, manage, and treat chronic diseases. Trends in pharmacological sciences, 39(9), pp.812-827. https://www.sciencedirect.com/science/article/abs/pii/S0165614718301196
  2. Narasimamurthy, R., Hatori, M., Nayak, S.K., Liu, F., Panda, S. and Verma, I.M., 2012. Circadian clock protein cryptochrome regulates the expression of proinflammatory cytokines. Proceedings of the National Academy of Sciences, 109(31), pp.12662-12667. https://pnas.org/doi/abs/10.1073/pnas.1209965109
  3. Panda, S., 2016. Circadian physiology of metabolism. Science, 354(6315), pp.1008-1015.  https://www.science.org/doi/abs/10.1126/science.aah4967
  4. Bunney, W.E. and Bunney, B.G., 2000. Molecular clock genes in man and lower animals: possible implications for circadian abnormalities in depression. Neuropsychopharmacology, 22(4), pp.335-345. https://www.sciencedirect.com/science/article/abs/pii/S0893133X99001451
  5. Pevet, P. and Challet, E., 2011. Melatonin: both master clock output and internal time-giver in the circadian clocks network. Journal of Physiology-Paris, 105(4-6), pp.170-182. https://www.sciencedirect.com/science/article/abs/pii/S0928425711000040
  6. Elverson, C.A. and Wilson, M.E., 2005. Cortisol: Circadian rhythm and response to a stressor. Newborn and Infant Nursing Reviews, 5(4), pp.159-169. https://www.sciencedirect.com/science/article/abs/pii/S1527336905001583
  7. Van Someren, E.J. and Nagtegaal, E., 2007. Improving melatonin circadian phase estimates. Sleep medicine, 8(6), pp.590-601. https://www.sciencedirect.com/science/article/pii/S1389945707000871
  8. Stephan, F.K., 2002. The “other” circadian system: food as a Zeitgeber. Journal of biological rhythms, 17(4), pp.284-292. https://journals.sagepub.com/doi/abs/10.1177/074873040201700402
  9. Valdez, P., 2019. Focus: Attention science: Circadian rhythms in attention. The Yale journal of biology and medicine, 92(1), p.81. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6430172/
  10. Lu, B.S. and Zee, P.C., 2006. Circadian rhythm sleep disorders. Chest, 130(6), pp.1915-1923. https://www.sciencedirect.com/science/article/abs/pii/S0012369215509215
  11. Gale, J.E., Cox, H.I., Qian, J., Block, G.D., Colwell, C.S. and Matveyenko, A.V., 2011. Disruption of circadian rhythms accelerates development of diabetes through pancreatic beta-cell loss and dysfunction. Journal of biological rhythms, 26(5), pp.423-433. https://journals.sagepub.com/doi/full/10.1177/0748730411416341
  12. Lecour, S., Du Pré, B.C., Bøtker, H.E., Brundel, B.J., Daiber, A., Davidson, S.M., Ferdinandy, P., Girao, H., Gollmann-Tepeköylü, C., Gyöngyösi, M. and Hausenloy, D.J., 2021. Circadian rhythms in ischaemic heart disease: key aspects for preclinical and translational research: position paper of the ESC working group on cellular biology of the heart. Cardiovascular Research.  https://academic.oup.com/cardiovascres/advance-article/doi/10.1093/cvr/cvab293/6368285
  13. Froy, O., 2010. Metabolism and circadian rhythms—implications for obesity. Endocrine reviews, 31(1), pp.1-24. https://academic.oup.com/edrv/article-abstract/31/1/1/2354749
  14. Asarnow, L.D., Soehner, A.M. and Harvey, A.G., 2013. Circadian rhythms and psychiatric illness. Current opinion in psychiatry, 26(6), p.566. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4000560/
  15. Vitale, J.A., Roveda, E., Montaruli, A., Galasso, L., Weydahl, A., Caumo, A. and Carandente, F., 2015. Chronotype influences activity circadian rhythm and sleep: differences in sleep quality between weekdays and weekend. Chronobiology international, 32(3), pp.405-415. https://www.tandfonline.com/doi/abs/10.3109/07420528.2014.986273
  16. Potter, G.D., Skene, D.J., Arendt, J., Cade, J.E., Grant, P.J. and Hardie, L.J., 2016. Circadian rhythm and sleep disruption: causes, metabolic consequences, and countermeasures. Endocrine reviews, 37(6), pp.584-608. https://academic.oup.com/edrv/article-abstract/37/6/584/2691715
  17. Schmidt, C., Collette, F., Cajochen, C. and Peigneux, P., 2007. A time to think: circadian rhythms in human cognition. Cognitive neuropsychology, 24(7), pp.755-789. https://www.tandfonline.com/doi/abs/10.1080/02643290701754158
  18. Lewis, P., Korf, H.W., Kuffer, L., Groß, J.V. and Erren, T.C., 2018. Exercise time cues (zeitgebers) for human circadian systems can foster health and improve performance: a systematic review. BMJ open sport & exercise medicine, 4(1), p.e000443. https://bmjopensem.bmj.com/content/4/1/e000443.abstract
  19. Kawai, M., 2022. Disruption of the circadian rhythms and its relationship with pediatric obesity. Pediatrics International, 64(1), p.e14992. https://onlinelibrary.wiley.com/doi/abs/10.1111/ped.14992
  20. Vasey, C., McBride, J. and Penta, K., 2021. Circadian rhythm dysregulation and restoration: the role of melatonin. Nutrients, 13(10), p.3480. https://www.mdpi.com/2072-6643/13/10/3480
  21. Kwok, C.S., Kontopantelis, E., Kuligowski, G., Gray, M., Muhyaldeen, A., Gale, C.P., Peat, G.M., Cleator, J., Chew‐Graham, C., Loke, Y.K. and Mamas, M.A., 2018. Self‐reported sleep duration and quality and cardiovascular disease and mortality: a dose‐response meta‐analysis. Journal of the American Heart Association, 7(15), p.e008552. https://www.ahajournals.org/doi/full/10.1161/JAHA.118.008552
  22. Brooks, C., Shaafi Kabiri, N., Bhangu, J., Cai, X., Pickering, E., Erb, M.K., Auerbach, S., Bonato, P., Moore, T.L., Mortazavi, F. and Thomas, K., 2021. The impact of chronotype on circadian rest-activity rhythm and sleep characteristics across the week. Chronobiology International, 38(11), pp.1575-1590. https://www.tandfonline.com/doi/abs/10.1080/07420528.2021.1937197
  23.   Moon, S., Kang, J., Kim, S.H., Chung, H.S., Kim, Y.J., Yu, J.M., Cho, S.T., Oh, C.M. and Kim, T., 2020. Beneficial effects of time-restricted eating on metabolic diseases: a systemic review and meta-analysis. Nutrients, 12(5), p.1267. https://www.mdpi.com/2072-6643/12/5/1267
  24. Almeneessier, A.S., Pandi-Perumal, S.R. and BaHammam, A.S., 2018. Intermittent fasting, insufficient sleep, and circadian rhythm: interaction and effects on the cardiometabolic system. Current Sleep Medicine Reports, 4(3), pp.179-195. https://link.springer.com/article/10.1007/s40675-018-0124-5
  25. Chow, L.S., Manoogian, E.N., Alvear, A., Fleischer, J.G., Thor, H., Dietsche, K., Wang, Q., Hodges, J.S., Esch, N., Malaeb, S. and Harindhanavudhi, T., 2020. Time‐restricted eating effects on body composition and metabolic measures in humans who are overweight: a feasibility study. Obesity, 28(5), pp.860-869. https://onlinelibrary.wiley.com/doi/abs/10.1002/oby.22756
  26. Hutchison, A.T., Regmi, P., Manoogian, E.N., Fleischer, J.G., Wittert, G.A., Panda, S. and Heilbronn, L.K., 2019. Time‐restricted feeding improves glucose tolerance in men at risk for type 2 diabetes: a randomized crossover trial. Obesity, 27(5), pp.724-732. https://onlinelibrary.wiley.com/doi/abs/10.1002/oby.22449
  27. Regmi, P. and Heilbronn, L.K., 2020. Time-restricted eating: benefits, mechanisms, and challenges in translation. Iscience, 23(6), p.101161. https://www.sciencedirect.com/science/article/pii/S2589004220303461
  28. Ruddick‐Collins, L.C., Morgan, P.J. and Johnstone, A.M., 2020. Mealtime: a circadian disruptor and determinant of energy balance?. Journal of Neuroendocrinology, 32(7), p.e12886. https://onlinelibrary.wiley.com/doi/full/10.1111/jne.12886
  29. Nakajima, K., 2018. Unhealthy eating habits around sleep and sleep duration: To eat or fast?. World Journal of Diabetes, 9(11), p.190. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6242722/
  30. Charlot, A., Hutt, F., Sabatier, E. and Zoll, J., 2021. Beneficial effects of early time-restricted feeding on metabolic diseases: importance of aligning food habits with the circadian clock. Nutrients, 13(5), p.1405. https://www.mdpi.com/2072-6643/13/5/1405
  31. Wahl, S., Engelhardt, M., Schaupp, P., Lappe, C. and Ivanov, I.V., 2019. The inner clock—Blue light sets the human rhythm. Journal of biophotonics, 12(12), p.e201900102. https://onlinelibrary.wiley.com/doi/full/10.1002/jbio.201900102
  32. Mure, L.S., Vinberg, F., Hanneken, A. and Panda, S., 2019. Functional diversity of human intrinsically photosensitive retinal ganglion cells. Science, 366(6470), pp.1251-1255. https://www.science.org/doi/abs/10.1126/science.aaz0898
  33. Bhandary, S.K., Dhakal, R., Sanghavi, V. and Verkicharla, P.K., 2021. Ambient light level varies with different locations and environmental conditions: Potential to impact myopia. Plos one, 16(7), p.e0254027. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0254027
  34. Hjetland, G.J., Pallesen, S., Thun, E., Kolberg, E., Nordhus, I.H. and Flo, E., 2020. Light interventions and sleep, circadian, behavioral, and psychological disturbances in dementia: A systematic review of methods and outcomes. Sleep Medicine Reviews, 52, p.101310. https://www.sciencedirect.com/science/article/abs/pii/S1087079220300538
  35. Stutz, J., Eiholzer, R. and Spengler, C.M., 2019. Effects of evening exercise on sleep in healthy participants: a systematic review and meta-analysis. Sports Medicine, 49(2), pp.269-287. https://link.springer.com/article/10.1007/s40279-018-1015-0?fbclid=IwAR2QyvZYq9rB5d0NkAfz7Yxv9usBgynVxgkG4po1zzHLX_VLiO1msm_NR_U
  36. Gabriel, B.M. and Zierath, J.R., 2019. Circadian rhythms and exercise—re-setting the clock in metabolic disease. Nature Reviews Endocrinology, 15(4), pp.197-206. https://www.nature.com/articles/s41574-018-0150-x

Insightful Excerpt from The Circadian Diabetes Code by Satchin Panda, PhD

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If you or a loved one has recently been diagnosed with prediabetes or diabetes, you are not alone. According to the U.S. Centers for Disease Control and Prevention (CDC), one in ten Americans has diabetes, and one in three is likely to have prediabetes right now. Just by reading this book, you are taking a very important step forward in managing your health.

Having a doctor tell you that you have prediabetes, or Type 2 diabetes is almost like running a temperature greater than 100.4°F. It’s a sign that some aspect of your health is off balance, and if you don’t pay attention, it can become much worse, potentially leading to life-threatening complications. Not only is diabetes linked to other chronic health conditions like obesity, heart disease, and Alzheimer’s disease, but it is also one of the most devastating underlying conditions related to intensifying infectious diseases.

Yet we know that even with diabetes, some days we feel better than other days. When we stop to think about it, those better days are typically the ones when we have slept well, ate nutritious foods, and even exercised. In the very same way, with these very same tools, anyone can learn how to control their diabetes, and possibly even reverse a diagnosis.

I’m on the forefront of circadian rhythm research, which is the science of our biological clocks. In my first book, The Circadian Code, I showed readers all over the world how every cell in the human body has a clock and keeps a schedule of when it is the optimal time for it to function. My research has fueled a whole new way of eating, which I call time-restricted eating (TRE), and is more commonly known as intermittent fasting (IF). Basically, my research shows that when it comes to weight loss, it’s not only what you eat that makes a difference.

To lose weight, it’s equally important to make good decisions about when you eat. My protocol not only works for weight loss; it also optimizes every cell in the body, including those that monitor blood glucose. If we nurture our circadian rhythm, it in turn nurtures our health. If you can control when you eat, you can reverse your prediabetes, manage your long-term or recently diagnosed Type 2 diabetes, and lose weight along the way. By doing so, you can also enhance every other aspect of your health.
How do I know all this? Just ask my mother.

Meet Mrs. Panda

I am lucky enough not to have prediabetes or diabetes—yet. However, I know that I have a high risk for developing diabetes and heart disease just by being from South Asia. For the past eight years, I have adopted an intermittent fasting lifestyle in which I try to eat within a fixed 10-hour window most days. This has helped me shed some extra weight. But the best results from intermittent fasting have been with my mother.

Seven years ago, my mother noticed the blood sugar numbers on her annual physical exams were creeping up. Over the next two years, her exams showed that her blood sugar was continuing to rise; in other words, she was approaching a diabetic state. Even though her doctor wasn’t really worried, she panicked because she knows the damage diabetes can cause. She had seen too many friends and relatives who ignored the early signs of the disease, and even after taking daily medications for years, they slowly developed heart disease, kidney disease, blindness, and even dementia. My mother was also less than thrilled about the idea of living with diabetes, having to carefully monitor what she ate at every single meal.

When she first told me the news, we talked about her daily diet and exercise routine, because it is well known that the foods you eat and the amount you exercise can influence your blood sugar levels. Yet even though she was already doing everything right, the results weren’t adding up. As a vegetarian, she would eat more than the recommended portions of fruits and vegetables every day, and she would take a daily walk in the evenings. She was also fasting at least once a week for religious reasons, while on other days she ate dinner by 8:00 p.m. But I noticed occasionally, at least two or three times a week, she would have a cup of tea with sugar and milk around 9:00 p.m. if she visited any of our relatives; it was difficult for her to decline a late-night snack.

I knew from my previous research that by eliminating this occasional and seemingly benign late-night snacking, she may be able to see some improvements in her blood glucose. When I first told her this, she laughed at me. Besides, her doctor and other health professionals could not be convinced that these small late-night meals were the culprit, pushing her toward diabetes.

A few months later I convinced her to visit me in the United States. When she lived with me for the next several months, she adopted my stricter rule of no food after 6:00 p.m. In the morning, she ate her breakfast around 9:00 a.m. That pattern created a daily eating window of 9 hours. Over the next several weeks, she told me that she had never felt better. And when she returned to India and continued eating this way, her blood sugar levels declined to below a prediabetic level. After five months, her fasting blood glucose was hovering near a healthy range. Best of all, for the past five years, she’s been able to stay healthy and off all medications—just by keeping to the protocol.

Since then, I have repeated this experiment in more than a dozen clinical trials. My group has worked not only with patients who have prediabetes but also those suffering from high cholesterol and high blood pressure. We always find that those who can follow a 10-hour IF can substantially improve their health.

Let Your Clock Control Your Blood Sugar

Now it’s time to try this experiment together. You can be in complete control of your blood sugar by living in alignment with your circadian rhythm. Not only is it easy, but also every aspect of your health will get better. In this book, you’ll learn when to eat, when to exercise, when to sleep, when to work, and when to take your medications, if necessary. If this program sounds simple, that’s because it is.

Your doctor may tell you to eat less, exercise more, and stay away from sugar and carbohydrates. There is sufficient research to substantiate these recommendations. However, the problem is in the compliance. Experts know that to follow these recommendations, you have to count calories for every meal you eat, track and avoid the foods that are known to raise your blood sugar, and count how many miles you walk or run. If you can do this, great; many people with prediabetes or diabetes begin this type of program and see some benefits within a month or two. But more often than not, the regimen becomes too difficult to sustain for a long time. Even though these are good habits to form, they are too arduous. This is where my research on circadian rhythm and time-restricted eating is opening new avenues for treating diabetes.

Research on circadian rhythm has shown that blood glucose regulation is more complex than we had known before. When we eat, when we exercise, and how much or when we sleep have a big impact on our blood glucose. By following this program, you may achieve your goals without counting a single calorie.

Excerpted from The Circadian Diabetes Code by Satchin Panda, PhD. Copyright © 2021 by Satchin Panda, PhD. All rights reserved.

Exercise and Brain Health

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• A Better Mood: Exercise-induced serotonin production may work as well as prescription antidepressant medications, according to a Cochrane review.
• Stress Relief: Anxiety disorders affect more than 40 million U.S. adults, but regular exercisers are at a lower risk for anxiety than those who are sedentary.
• Better Brain Power: According to University of British Columbia researchers, people who engage in regular heart-pumping, sweat-producing exercise have a larger hippocampus (the area in your brain involved in memory and thinking) than those who don’t exercise.
• A Natural High: Want a natural high? German researchers found that the same area in the brain that is altered by the THC in marijuana also seems to be activated by exercise.

You know that exercise is good for your body, but you might not realize all the ways it helps brain health as well. You may have heard that heart-pumping, sweat-inducing physical activity floods your body with feel-good endorphins that improve your mood, but that’s just the beginning. When compared to non-exercisers regular exercisers have better memories, reaction times, enhanced comprehension, lower stress, and improved moods. Indirectly and without any conscious thought, these positive benefits can boost your motivation to help you keep exercising regularly. Studies show that just one bout of exercise, even just 10 minutes, causes changes in your neurochemistry that reduces sadness, improves energy, and boosts happiness more than being sedentary. Exercise also helps brain health by enhancing heart health, blood sugar levels, insulin sensitivity, weight management, and better digestion.

Have you ever noticed that “good tired” feeling that comes after an unusually active day? Maybe it was an over-zealous workout session, perhaps you just got caught up last Sunday on yard work. These activities might leave your muscles feeling fatigued, but they can also bring feelings of relaxation, serenity, energy, and happiness. It’s not your imagination. Exercise can be as powerful as medicine when it comes to improving your mind, mood, and motivation. Let’s take a look at just some of the benefits of a brain on exercise:

A Better Mood: Physical activity stimulates the release of feel-good chemicals in your brain. When you exercise, endorphins are signaled. These are your body’s natural pain killers, and they also can shut down negative and self-destructive thinking. Also, mood-boosting serotonin is triggered and increased in your brain when you exercise. Exercise-induced serotonin production may work as well as prescription antidepressant medications, according to a Cochrane review, researchers analyzed 23 exercise and depression studies and concluded that exercise worked as well as many medications and worked slightly better than therapy alone.

Stress Relief: Regular participation in physical activity can reduce anxiety and stress and enhance relaxation. Anxiety disorders affect more than 40 million U.S. adults, but regular exercisers are at a lower risk for anxiety than those who are sedentary. In another study of nearly 20,000 people, those who exercised moderately for 30 to 45 minutes most days of the week reported lower rates of anxiety and neurosis compared to non-exercisers. No time for a long workout? No worries, research shows that a 10-minute walk can reduce stress and boost mood as well as longer workouts.

Better Brain Power: Got brain fog? Get moving. According to University of British Columbia researchers, people who engage in regular heart-pumping, sweat-producing exercise have a larger hippocampus (the area in your brain involved in memory and thinking) than those who don’t exercise. In other research, neurologists have found a link between moderate exercise and an increase in the volume of selected brain regions that are linked to better brain function.

A Natural High: You’ve heard of the “runner’s high,” but many people regularly report that they feel a natural sense of euphoria after any sort of exercise. Research points to the release of endorphins that trigger a response that is similar to opioid drugs. Plus, German researchers found that the same area in the brain that is altered by the THC in marijuana also seems to be activated by exercise.

Other Exercise-Induced Brain Benefits
Insulin sensitivity: Exercise improves insulin sensitivity and blood flow in dopamine-related brain regions and blood flow to all areas of the brain, according to a recent study published in the Society for the Study of Ingestive Behavior. Brain scans done before and after an eight-week exercise program (walking and biking) found that exercise increased blood flow and insulin regulation in areas of the brain important for motor control and reward processes (dopamine-related regions). The results, according to researchers, may help decrease the risk of diabetes and diabetes-related conditions.
Weight control: Exercise is a crucial part of losing and maintaining a healthy weight, but how does managing weight help your brain? Besides improved blood flow, oxygen, and other nutrients for your brain, a new study finds that the link between exercise and weight management may reduce aging effects in your brain. The researchers, who did MRIs on more than 1,000 adults, found that those who had the highest weights showed the most prominent decline in the brain cortex, which has been linked to aging and dementia.
Heart health: Exercise reduces arterial damage that can cause heart disease and attacks, and it’s this heart health that also reduces artery blockages that damage blood flow and oxygen delivery to your brain. Studies also show that people who have higher markers for heart disease have an increased risk for Alzheimer’s dementia.
Gut health: There’s big news these days about all the ways that the nearly 100 trillion microbes in our guts affect our brain health. Many studies suggest that imbalances in the gut are linked to anxiety disorders and neurodegenerative diseases like Alzheimer’s disease. Exercise, according to other research, can help enhance and enrich the number of beneficial microbes in your digestive tract, which can reduce related brain disorders and aging.

Moving provides a physical release that lowers anxiety and stress while energizing your body and empowering your mind. Exercise helps you to think more clearly, to be more focused, and to have a better memory. Don’t think about it, throw on some supportive walking shoes and get out there and start moving. Start with as little as a walk around the block and work up, block by block, each day after that. Aim to move 30 to 45 minutes for five or more days per week. You’ll feel better, and your body and brain will thank you.