A circadian rhythm is a roughly 24-hour cycle in the physiological processes of most living beings. Circadian rhythms are self-sustained, but they are susceptible to alterations depending on external environmental coming from such as light and temperature. Circadian rhythmicity is particularly present in the wake-sleeping-cycle and feeding patterns of all animals (including humans) and plays an important role in the prediction of seasonal changes, food availability and predator activity that is crucial for the survival of many species.
Circadian rhythms have also been linked to meal times and physical activity. Regular meal times throughout the day allows the body to move closer towards a para-sympathetic (rest and digest) state in preparation for food to come. The body produces digestive enzymes and upregulates metabolism when meal times are regular. The same is true for physical activity if you train at the same time of the day your body can upregulate sympathetic hormones in preparation for the “fight or flight" for training
Very simply put, circadian rhythm is a biological clock that regulates all physiological processes connected to hormone production, including sleep, metabolism and reproduction. When our body clock works optimally, we feel awake and energised in the morning due to the creation of cortisol, while melatonin production stops with exposure to light. After experiencing a peak in testosterone production during the day, at sunset the hormone leptin, which suppresses hunger and produces heat to keep the body warm at night, is released. Melatonin, the hormone that signals sleepiness, is usually secreted around 9 pm, followed by the growth hormone which allows us to repair and recover during sleep.
Circadian rhythms vary depending on individual chronotypes, behavioural preferences to sleep earlier or later within the day. Chronotypes seem to be closely linked to age (adolescents prefer going to bed late, the elderly tend to sleep earlier), genes, light and darkness, feeding times and schedules. Depending on whether you are more of a “morning” or an “evening person”, understanding your chronotype and behaving can help you sleep better, have a more balanced hormone production and manage stress.
People who work night shifts have shown to be prone to reduced immune function often causing chronic diseases and cancer. Shift workers are often sleep deprived, which impairs the body’s ability to maintain homeostasis and increases the risk of disease and lowers life expectancy.
Our sleep cycle is determined by two main factors, the first being sleep pressure, which builds up from the moment we wake up and helps us fall and stay asleep at night, and wake drive, which also starts building up from the morning to counteract the effects of sleep pressure. Wake drive decreases according to routine around our usual bedtime, allowing sleep pressure to take over for optimal sleep. Our goal should be to sync wake and sleep-drive to be able to feel energised during the day, when most of our social behaviour (should) happen, and sleepy at night when the body expects to be able to rest.
The creation of artificial light has been a significant disruption on the regularity of most people’s circadian rhythm. We are now able to keep working, using computers and mobile phones, interact with other people well beyond what our body clock perceives to be the time to sleep. This delay in sleeping time (a push to our wake drive beyond its natural cycle) can cause difficulty falling asleep and the feeling, familiar to many, of daylong sleepiness.
Melatonin production decreases as a result of exposure to artificial light: avoiding using electronic devices for at least an hour before bedtime can help improve sleep quality. It’s also essential to minimise the sources of artificial light in the bedroom at night time by using blackout curtains and turning electronics off.
The temperature in your bedroom can also have an impact on the quality of your sleep: we advise to keep the environment you sleep in as cool as possible.
Avoid creating connections to stressful situations in the bedroom by using it only for sleep and sex and especially avoiding upsetting conversations while in it. If you work from home, it would be a good idea to work from a different room.
Diurnal and nocturnal rhythms are disrupted by the use of stimulants such as caffeine, nicotine, alcohol and similar drugs. Drinking tea and coffee can be an aid to raising wake levels in the morning, but for people who are experiencing trouble sleeping it is not advisable to consume such drinks after 3 PM (the half-life of caffeine is 6hours). Slowly reducing the amount of caffeine ingested daily can be of considerable help to improve sleep at night.
Physical activity has an impact on the way we sleep: it can be extremely beneficial when done in correct amounts but can lead to insomnia if practised in excess. Exercising for health is very different from exercising for performance (which often requires multiple daily workouts, many high-intensity sessions, long training days), and often athletes need to deal with high levels of inflammation, hormonal imbalances and physical stress.
If your goal is not to compete but to feel, improve health and longevity, an hour-long workout with varying intensities, depending on your age and lifestyle will do marvels for your health and sleeping patterns in particular. What is a healthy and sustainable form one person can be far too much for another, just like diet there is not a one-size-fits-all approach to training.
Just as for physical activity, it is essential to find an appropriate meal frequency and try to eat enough but not too much before going to bed. If you have trouble sleeping eating a carbohydrate- snack before bed can increase your chances of getting to sleep. Carbs increase the production of tryptophan, a hormone that precedes the production of serotonin, which is a precursor to melatonin production.
In the morning, responding to the production of the hunger hormone ghrelin by eating breakfast can also help restore your circadian rhythm, release dopamine and other hormones that increase energy and focus.
Restoring circadian function may seem like an impossible task to many, but many sustainable and straightforward changes can be made to improve it:
Try going to bed ten minutes earlier and getting up ten minutes earlier.
Avoid eating the bulk of your daily calories at night time but allow yourself a snack before bed.
Turn off all screens (TV, computer, phone) 1-2hours before your plan on going to bed.
Plan your schedule and make sure to reserve time for sleep just as you do for work or social activities you enjoy.
Drink one less coffee during the day.
Limit alcohol intake
A small change can make a big difference in the long run.
Cruz, R., et al. Pacing Strategy and Heart Rate on the Influence of Circadian Rhythms. Journal of Exercise Physiology, 2013
Pain, S., et al. The Epidemiology of morningness/eveningness: influence of age, gender, ethnicity and socioeconomic factors in adults (30-49 years). Journal of Biological Rhythms, 2006, pp.68-76
Bominak, S., Stumpf, W., The World Epidemic of Sleep Disorders Is Linked to Vitamin D Deficiency. Medical Hypotheses, 2012.
Jaminet, P. Circadian Rhythms: Their Significance in Human Health, and the Major Factors Affecting Them. Ancestral Health Symposium, 2013.