How to improve your circadian rhythm

Ever wondered why your body’s systems feel all jumbled when you travel across time zones, or if you work nightshifts?

It’s because these things can wreak havoc on your circadian rhythm. We dive into what your circadian rhythm is, what can disrupt it and how you can support yours, along with why the original idea that people have one body clock was wrong…

What is circadian rhythm?

Circadian rhythms are essentially rhythms of life – rhythmic fluctuations in behaviour, physiology and metabolism that happen in cycles, usually over a 24-hour period. Circadian means “around the day”. The time you fall asleep and wake up are heavily influenced by these circadian rhythms.

As the earth rotates around its own axis and around the sun, we’re subject to predictable daily changes in light and dark, food availability and seasons. To adapt to and anticipate these daily changes, most organisms have evolved an internal timing system known as circadian clocks.

We have a master clock in a specific area of our hypothalamus in our brain called our suprachiasmatic nucleus (SCN) which is calibrated on a daily basis by external signals coming from our surroundings. The hypothalamus is an important control centre that regulates key hormones and our autonomic nervous system.

For the SCN to function properly, our eyes and skin need regular exposure to unfiltered natural daylight.

It’s the way our bodies recognise where we are in the 24-hour cycle and what season it is, so that we can co-ordinate and be ready to do the right things at the right time. Light and dark cycles of the day are detected by light responsive pigments in our eyes and skin.

As you’re reading this, your body is carrying out an incredible number of processes. In health, all these processes work in synchrony together, in response to external cues (primarily light). It’s a process called entrainment.

There isn’t just one master body clock. We now know almost all cell types – including fat cells, heart cells, and liver cells, amongst others – contain clock genes, secondary internal clock mechanisms, that contribute to the tapestry of our body’s functions.

What impacts our circadian clocks?

Zeitgebers mean “time givers” and are the external cues from your environment to “turn on” your clock genes. The primary zeitgeber is light, but there are others:

Social interactions, food availability, exercise, and depending on where you live, tides, temperature and moonlight can also act as zeitgebers. Your body learns how to respond to particular events triggered by external cues and follows established patterns. The important thing to remember is that we can control many of these external zeitgebers.

What is impacted by our circadian rhythms?

Most important functions in your body are impacted by circadian rhythms:

• energy production
• hormone release
• digestion
• body temperature and
• most noticeably, your sleep cycle

So, the harmony of your circadian rhythm is crucial for many aspects of your wellbeing, such as sleep, metabolism, and both cardiovascular and immune health.

What can disrupt your circadian rhythm?

Common circadian rhythm disruptors are:

• shift work
• travel across time zones
• pulling all-nighters or burning the candle at both ends studying or partying
• lack of natural daylight
• drugs and alcohol

What are the consequences of circadian rhythm disruption?

In the short-term circadian rhythm disruption can lead to impaired:

• mood
• sleep and
• cognition

Long-term circadian rhythm disruption could increase susceptibility to:

• cancer
• obesity, weight gain and disorders of metabolism
• cardiovascular disease
• psychological conditions, being particularly associated with major depressive disorder and bipolar disorder
• the effects of ageing and neurodegenerative disease

How to improve your circadian rhythm

1. Get outside in morning light soon after waking

The retina of your eyes contains the vitamin A-based photopigment melanopsin, which is activated by the blue light component of daylight. Melanopsin signals your master clock that it’s daytime.

What we’re starting to understand about light is that, to regulate our circadian rhythm and the many rhythmic body functions it supports, we need exposure to a broad range of light wavelengths (from UV to visible light and infrared) at differing levels of intensity throughout the day (generally more in mornings and less in evenings). It’s tricky to get this from artificial light alone, so it’s becoming increasingly clear that getting out into natural light is a vital contributor to regulating our circadian rhythms.

Insufficient light in winter increases the risk of depression, possibly due in part to the lack of light activation of melanopsin. Melanopsin also controls the production of the sleep hormone melatonin (see below).

Central retinal pathways in your eyes also project light to the front lobe of your pituitary gland, a pea-sized gland at the base of your brain below your hypothalamus that controls the release of other key hormones that support the management of stress, growth, pain relief and reproduction.

While we’re on the topic of getting outdoors, it’s worth mentioning that there’s a school of thought that advocate having direct contact with the earth (known as ‘earthing’ / ‘grounding’) may have a positive impact on regulating circadian rhythm. Evidence to support this theory is currently inconclusive, but it certainly can’t do any harm to get outside in the mornings and enjoy a little bit of barefoot contact with the earth, whilst getting that all important dose of natural sunlight.

2. Make the night-time screen a has-been!

Melatonin, on the other hand, is the hormone of darkness produced by our pineal gland which prepares us for sleep, regulates circadian rhythms, and has other important functions and benefits. It’s feel-good serotonin, which makes us feel more awake and energised, that’s converted into melatonin during the night.

Your levels of melatonin rise during the night and lower during the day. If you’re staring at filtered “blue” light emitted by your phone before you go to sleep, your retinal cells receive confusing signals thinking it’s daytime suppressing melatonin, which, amongst other factors, may disrupt your sleep.

Aim to keep your bedroom an electronic screen-free zone. There’s lots of speculation as to whether dark, night modes or blue light blocking devices are effective at preventing circadian rhythm disruption, but what we do know is that we should reduce our exposure to artificial light in the crucial hours before sleep.

3. Embrace cold showers

The multiple benefits of cold showers have been known about for centuries, but the mechanisms aren’t completely understood. The rhythms of your body temperature and metabolism are managed by your circadian clocks. Along with light, temperature is thought to be one of the environmental cues that can regulate your body’s master clock. Studies suggest that by exposing yourself to cold temperatures you may be able to jump start your circadian rhythm by stimulating circadian neurons (cells in your nervous system that transmit information to other cells) and the energy powerhouse of your cells, known as your mitochondria.

Exposure to cool temperatures in the mornings (or when you wake up if you’re a shift worker), either with a cold shower, bath, or wild swimming if you’re feeling adventurous, could help jump start your circadian clocks and boost energy and heat production.

Should you wish to wake up earlier in the day, opt for a cold shower in the morning when you wake up. This will raise your body temperature naturally quicker than it would without the cold shower, as your body rebounds from the cold. The result? You’ll want to go to bed sooner and wake up earlier the next day.

Reading that may have made your shiver, but why not give it a try for a few days and see if it works for you?

4. Ensure you’re getting enough vitamin A and DHA

Animal studies have illustrated that a deficiency in vitamin A, necessary for melanopsin, can disrupt the circadian rhythm and may result in cognitive impairment. Food sources include oily fish (think tasty salmon, mackerel, trout and sardines) eggs, cheese, milk and yoghurt. Liver and related products like liver pâté are especially rich in the vitamin, so be mindful to have it just once a week to avoid having too much vitamin A and avoiding it all together if you’re pregnant.

You can also get vitamin A via beta-carotene found in yellow, red and green (leafy) vegetables. For example, spinach, carrots, sweet potatoes and red peppers, and yellow fruit, such as mango, papaya and apricots. Your body will convert the beta carotene into vitamin A, so you can add these foods to the list!

While you’re at it, weaving sources of DHA (docosahexaenoic acid), such as mackerel, salmon, herring, sardines, shellfish, and cod liver oil into your diet may help support your melatonin levels as some animal studies show.

5. Make routine your best friend

Regular mealtimes play a role in synchronising the secondary cellular body clocks, though they seem to have less effect on the SCN. Eating during daylight hours complements your circadian rhythm, so, as a starting point, try eating within an 8–12-hour window as this benefits many of your organ systems. Some experts, such as Professor Satchidananda Panda, PhD, recommend avoiding food and drink in the first hour after you wake up and 2-3 hours before you go to bed. This allows your circadian clocks to fully wake your metabolism hormones, such as insulin, and digestive process when you rise, and gives your body enough time to ‘rest and digest’ before sleeping. Have a play and see what works for you.

Regular wake-up and bedtime

Ever wake up just before the alarm you set every day? This is your circadian rhythm at play! Adults aged 18-64 need around 7-9 hours of sleep, whilst the recommended sleep time for those aged 65 and above is 7-8 hours. You’ll intuitively know how much sleep you need to function at your best.

Regular exercise – preferably outdoors

It’s unclear if the same advantage of a regular routine applies to exercise. However, one study of 100 men and women aged between 18 and 75 who were all considered to be aerobically fit shows you might be able to reset your circadian rhythm by exercising at certain times of the day. The researchers discovered exercising at 7am or between 1pm and 4 pm progressed the body clock enough that people could be active earlier the following day, feeling more refreshed sooner after waking up in the morning. Exercising between 7pm and 10pm though, delayed the body clock, meaning participants struggled to get to peak-performance mode until later the next day and felt more sluggish when they first awoke but energised later. These findings could be handy for shift workers who do nights, as adapting to work-out in the early evenings would delay their circadian rhythm, resulting in hitting their peak performance later when they need it most.

Whatever time you decide to exercise, it’s a good idea to avoid exercising 90 minutes before going to sleep. Doing so allows your body temperature, which rises during exercise, to return to one that’s more favourable to falling asleep.

Experiment with adjusting your routine and see how you feel!

You may already be doing some of the tips above, but of the circadian rhythm-friendly habits you’re not regularly practising, which one might you try first?

Reviewed by:

Anna Keeble MA BA Wellbeing Expert

Dr Claire Marie Thomas MRCGP DFSRH DTMH DipNLP MBChB BMedSci Clinical Content Lead

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