How to maintain a healthy circadian rhythm 

Our circadian rhythms are the internal clocks that help our body “tell the time” and determine when different biological processes should be active and when they should rest. Circadian rhythms are not solely for humans, either. Internal rhythms drive plants to open their leaves at dawn and close them at night, fruits to open or remain closed, and mammals to sleep, eat, mate and migrate. Almost all living organisms have circadian rhythms — plants, animals, microbes, fruit and even the bacteria in our gut(1). In fact, there is an entire scientific field called chronobiology dedicated to the study of circadian rhythms.  

Based on the evidence, we’d like to highlight five ways you can achieve a healthy circadian rhythm.  

1. Get natural daylight first thing
2. Eat within a timed window
3. Try Intermittent fasting 
4. Reduce artificial light in the evening 
5. Go to bed at the same time each evening 

Each of these will be covered in detail, but first we’d like to talk about the biological processes and functionality of the human circadian rhythm, as well as the role melatonin plays in regulating sleep.  

What is a circadian rhythm? 

In humans, our circadian rhythm is controlled by a group of around 20,000 nerve cells (neurons) in the brain called the suprachiasmatic nucleus, or SCN, which is central to the maintenance of our internal body clock. The SCN clock is set to solar time by photic input pathways found in the retina of our eyes. This regulates our core body temperature, which in turn triggers various cells within our different organs to switch on and become active, or slow down, as well as our hunger, sex drive and melatonin production (which contributes to our sleepiness). Although the genes and proteins generally determine individual rhythms, external factors related to light and dark also have a significant impact on how our body tells the time, and our peripheral clocks are also sensitive to nutrient availability.  

The different circadian rhythms in the body 

We don’t just rely on circadian rhythms to regulate our sleep patterns. Circadian clocks have now been identified in almost all tissues and cell types, where they regulate local metabolic processes, cell regeneration, glucose and lipid homeostasis, hormone release, immune response, gastrointestinal motility and digestive processes(2).The clock doesn’t arrive pre-programmed from our birth, however. When babies are born, their internal clocks aren’t synchronised with the external, 24-hour cycle of daylight and darkness — it takes time for babies to get in sync, which is why their sleep and eating patterns are so sporadic.  

The circadian rhythm and sleep 

The SCN is entrained by the sleep/wake cycle, which plays a major role in maintaining the healthy functioning of our circadian rhythms. SCN neutrons adjust their circadian phase according to the input of ambient light levels, and it has been found that light has two distinct effects on circadian rhythms: 1) the acute suppression of melatonin, 2) shifting one circadian phase into another. The effect of morning light is that it advances the clock, while evening and night light delays the clock. However, scientists now know that acute and long-term light exposure are not driven by the same pathways, which explains why one night of restless sleep and smartphone gazing might make a person feel tired the following day but does not have a long-term effect on the body. Rather, the light-response system follows multiple pathways, instead of just passing through the SCN. But as for which area of the brain is responsible for processing acute light, research is still not conclusive. When we know more, we’ll be able to understand how to optimise light exposure to increase alertness in those who need it, for example shift workers, while mitigating the harmful effects of shift work in circadian rhythms(3)

The role of melatonin 

When we wake up and natural light enters our retina, it sends a signal to our SCN to kickstart certain biological processes. If we wake up too early and try to perform an activity when our body isn’t yet alert, our performance is more likely to suffer. In fact, studies have shown that there is a higher incidence of motor vehicle accidents in the early morning hours than in the afternoon, when our circadian rhythm is at its peak. 

Both melatonin and circadian rhythms impact reproduction as well, especially during pregnancy. Since melatonin is produced in both the ovary and in the placenta, where it protects against molecular mutilation and cellular dysfunction, it’s important for expectant mothers to maintain a regular sleep/wake cycle. The mother’s circadian clock, either directly or indirectly, programmes the developing master oscillator of the foetus. And experimental studies have shown that disturbed maternal circadian rhythms and melatonin cycles have negative consequences for the developing foetus, which may to lead psychological and behavioural problems in the newborn. In fact, studies have found that low levels of light exposure in newborns may influence the onset of bipolar disorder, autism, anxiety-related disorders such as schizophrenia(4).  

5 ways to achieve a healthy circadian rhythm:    

1. Get natural daylight first thing 

When you wake up, exposure to light triggers your brain to produce less melatonin which, in turn, kickstarts various biological systems. As soon as your alarm sounds each morning, open the blinds and get some natural light in to help reset your internal clock. Moreover, time changes and daylight saving can disrupt our circadian rhythms. To mitigate this, experts recommend that before a time change, you start waking up a little earlier the week before, and going on morning walks or eating breakfast outside to increase your light exposure and regulate your circadian rhythm.  

2. Eat within a timed window 

The SCN in the brain is also entrained by feeding and fasting periods. Snacking round the clock, and especially before we sleep, can have a detrimental effect on the internal clock. Studies have found that circadian clocks in multiple tissues – such as the liver or pancreas – contribute to glucose homeostasis (the balance of insulin and glucagon to maintain optimal blood glucose levels). And there is an increasing amount of evidence that demonstrates the intricate link between the timing of our meals and our glucose tolerance. 

One study found that patients who ate 5 hours later than their peers in the evening then showed a significant delay in the circadian rhythm of blood glucose regulation(5).  

Just a simple action of eating too late in the evening can negatively affect the pancreas, preventing it from creating adequate insulin levels to mop up glucose in the blood. In another study, individuals were assigned to a “circadian misalignment” protocol and told to sleep from 11pm-7am for 3 days before switching to sleeping from 11am-7pm for the latter 4 days. Critically, this prolonged exposure to circadian misalignment resulted in declining glucose tolerance — the result of reduced insulin secretion from the pancreas(6).  

The liver is also affected by the time you eat. When the SCN triggers the release of melatonin in the evening, it also sends signals to the liver to tell it to stop creating enzymes to turn calories into energy rather than storing food as fat. Thus, the more food you put into your body at night when melatonin production is at its peak, the harder your liver has to work to convert the calories into fuel. 

3. Try Intermittent fasting  

Intermittent fasting or time-restricted eating can help support your circadian rhythm because the hormones in our gut play a critical role in modulating gastric emptying, and the glycemic response to meals. By giving yourself a window period within which to eat, for example 10 hours, and stopping eating at 6 or 7pm in the evening when gastric emptying is at its most sluggish, you start to eat in tune with your body’s internal clocks which are in tune with the light/dark cycle. The fasting can be done during the hours that you sleep, and experts recommend giving your body between 12-16 hours without food to completely reset by morning. We wrote more about the different types of intermittent fasting here.   

4. Reduce artificial light in the evening  

If we’ve learned anything so far, it’s that the body clock is wound generally to correspond to light and dark. So, what happens when you flip the light switch in the evening, look at your phone or turn on the television? The blue light that is emitted from electronic devices — including lights in your home — tricks the brain into thinking it’s still daytime and to delay the release of melatonin, the hormone that makes us feel sleepy. Artificial light throws the body clock into disarray, so it’s best to switch off electronic devices or use the built-in night setting which automatically reduces the amount of blue light emitted. We wrote more about this in an earlier blog on using amber light in the evening.   

Wearing glasses that block out excessive blue light also helps your body’s melatonin release sync with the sun’s descent, triggering the onset of sleepiness. TrueDark glasses provide a 24-hour solution that mimics your natural body clock, helping you to improve sleep and entrain your circadian rhythm.  TrueDark Twilights are specifically designed to work with melanopsin (a protein in your eyes that is responsible for absorbing light), to help signal to your brain to wind down and get ready for bed.  

5. Go to bed at the same time each evening 

On average, and depending on where you live in the world, melatonin usually begins triggering the body to rest around 9pm, and starts slowing down around 7:30am. Orientating your sleep schedule around these average times, with extra time to wind down before bed, can therefore help to align your circadian rhythm on a daily basis(7). Treat yourself to a generous wind down period at the end of the day, which might include reading, yin yoga, meditation or an evening gratitude practice. Be aware that bedtime procrastination is a common issue, with blue light exposure often contributing to a feeling of alertness, which leads to many of us unintentionally postponing bedtime. Find out our 3 tips to break your bedtime procrastination habit here.   


We know that circadian rhythms are affected by light, food timing and external factors such as electronic devices and time changes. Light at the wrong time may disrupt circadian rhythms and sleep, but in the form of light therapy, light exposure can be used as an intervention for health conditions and people who perform shift work. To keep your circadian rhythm functioning healthily, try to get some natural light each morning for 10-15 minutes to activate your internal clock. Introduce food timing and a fasting period to help optimise your liver, pancreas and sleep, and stop eating at least 4 hours before you go to bed to enable your liver and digestive system to reset.  

Switching off electronic devices or turning on the night setting, as well as wearing blue light blocking glasses as soon as the sun goes down can help mitigate the harmful effects of screens. You can even use a red-light therapy device in the evening, to mimic the natural sunset to promote melatonin production. Finally, eating foods that are high in tryptophan, like turkey, eggs, salmon and pumpkin seeds as well as performing calming exercise in the evening such as yin yoga or a walk can help produce the relaxation hormone serotonin, leaving you primed for a healthy dose of deep sleep. 

There are plenty of ways you can help support your circadian rhythm, and as we gain more understanding, we’ll be better able to use light and food in ways to optimise our bodies, and therefore our health and longevity.  

1 Microbiota Diurnal Rhythmicity Programs Host Transcriptome Oscillations 
2 Chronobiological aspects of nutrition, metabolic syndrome and obesity 
3 Newly discovered neural pathway processes acute light to affect sleep 
4 Melatonin and stable circadian rhythms optimize maternal, placental and fetal physiology 
5 PERSPECTIVE: The Long-Term Effects of Light Exposure on Establishment of Newborn Circadian Rhythm
6 Meal Timing Regulates the Human Circadian System
7 Matching Meals to Body Clocks—Impact on Weight and Glucose Metabolism