Unlock the power of your body clock

Could eating, sleeping and exercising according to our natural, internal rhythms be the key to optimal wellness? Read on to find out.

As anyone who’s flown long-haul can attest to, mess with your body clock at your peril. The symptoms of jet lag aren’t just being wide-eyed at 2am or falling asleep during the lunchtime news. Readjusting to a new time zone can leave you feeling decidedly off-colour and experiencing nausea, constipation, anxiety and dizziness as a result, according to the NHS._[1]

But experts are now sounding the alarm that the demands of our 24/7, hyper-connected lifestyles mean we're living in a constant state of self-imposed jet lag, and that’s not great news for our health. We know, for example, that shift workers are at much greater risk for a host of metabolic disorders, obesity, heart disease and depression._[2]

Even if you’re tucked up in bed by 10pm every work night, you could still be at risk of disrupting your body clock if the way you live at the weekend is dramatically different from your weekday schedule.

The term ‘social jet lag’ was coined by Till Roenneberg, professor of chronobiology at Ludwig-Maximilian University in Munich. Speaking to the Guardian, he said that our weekend practices of staying up later, having a Saturday morning lie-in and a more unpredictable eating pattern (hello, Sunday brunch) “promotes practically everything that’s bad in our bodies,” including weight gain, reduced mental performance and chronic illness.

He estimates that two-thirds of us experience at least one hour of social jet lag a week, and a third experience two hours or more – the same as flying from London to Tel Aviv and back, each and every week._[3]

Circadian rhythms

Every organism in nature operates in a cyclical way. The human body, too, tries to coordinate all of its systems by use of a central internal clock in a predictable, daily pattern. But how does it all work?

Our body clocks are governed by circadian rhythms, 24-hour cycles of physical, behavioural, and mental changes, regulated by both external and internal cues. Circadian rhythms oversee the daily rise and fall of hormone levels, body temperature, blood pressure, metabolism, digestion and more.

For example, our body temperatures fluctuate during the day, dropping to their lowest at 4am and peaking in the early evening (which is why fevers get worse at this time). Blood pressure rises sharply each morning when we wake up, coinciding with the time when blood platelets are stickiest (which helps explain why many heart attacks happen in the early hours)._[4]

Circadian rhymes are also behind medical phenomena such as ‘sun-downing’, when people with Alzheimer’s and Parkinson’s become distressed and confused in the late afternoon._[5]

Speaking to Nature, Derk-Jan Dijk, director of the Surrey Sleep Research Centre in Guildford said the entire body is like “a house with clocks in every room and every corner, yet in one way or another they work in an organised way.”_[6] These clocks are made up of proteins that interact with cells throughout the body._[7]

Light plays a huge role in how the master clock in the brain is ‘set’. When photoreceptors in the eye detect light, it switches on a host of physiological responses, including suppressing production of the hormone melatonin, inducing wakefulness.

But while light is the brain’s master switch, the body also uses various lifestyle cues, such as meal timing and physical activity, to regulate the rhythms of its peripheral ‘clocks’, housed in cells all over the body. Your gut bacteria, skeletal muscle, the nervous system and even skin cells are primed to do different things at different times of the day.

Take digestion, for example. Colonic motility changes during the day, being suppressed during the night and most active in the morning. A disordered eating schedule (for example when you’re travelling or trying a new intermittent fasting diet) can disrupt the colon’s 24-hour pattern, and lead to constipation._[8]

So if this internal rhythm plays such an important role when it comes to our health, could working with it rather than against it be good for us? That’s what the exciting new science of chrono-biology, along with its off-shoots of chrono-nutrition, chrono-exercise and chrono-pharmacology, are trying to discover.

What is chronobiology?

Chronobiology is a field of biology that studies the internal timing processes (or circadian rhythms) of living organisms, including humans.

Many chronobiologists believe we can use this information to improve our lives. For example, in the growing field of chrono-pharmacology there’s thought to be an ideal time to take medication. Fascinating research from the University of Birmingham has shown that flu vaccinations are far more effective when administered in the morning, for example._[9]

How to tweak your daily routine for optimal health

Chronobiologists believe that many common physical complaints (lack of energy, poor sleep and weight gain) are caused by a modern schedule at odds with our body clocks. By tweaking our daily routines (and sticking to them each day, including at weekends) you’ll be giving the body the predictable signals it needs to function efficiently.

So what does this look like in practice? Here’s when to eat, sleep and exercise to give your body exactly the right stimulus at the right time for optimal health.

• Best time to eat

Having your largest meal earlier in the day could be good for your health, according to chronobiologists at Harvard Medical School._[10] Their research indicated that late-night eating was associated with increased obesity risk, increased body fat and impaired weight loss success.

Harvard researchers took 16 overweight and obese patients and gave them two protocols to complete, one with an early meal schedule, and the other with the same meals but scheduled four hours later in the day. Eating later had profound effects on the appetite-regulating hormones leptin and ghrelin and participants burned calories at a slower rate

It seems your digestive tract has a 24-hour rhythm too, secreting the most gastric juices, enzymes and hormones in the first half of the day. In the late evening the body is less able to metabolise sugar, calories and fat. In short, the exact same meal could be far healthier eaten at 5pm than 9pm.

The relationship between food and your body clock is a two-way street: Your circadian rhythms influence how well your body handles food at different times of the day, but eating also helps train your body clock._[1]

• Best time to exercise

One of the ways the body tells the time is through physical activity. When you are physically active the body logically assumes it’s daytime, making morning a great time to exercise.

Even if you only manage light stretching when you wake up, you’ll be giving your body strong signals that the day has started, priming it to start its daily cascade of physiological processes. And if you can pair your morning exercise with a blast of outdoor light (like a quick stroll outside) you’ll be entraining your circadian rhythms even more effectively._[12]

Conversely (and in bad news for evening gym-goers) exercising intensively at night can inhibit the production of melatonin that tells the body it’s time to start winding down._[13]

But it’s not just your sleep that will feel the benefit from switching up your exercise routine. In a recent study carried out in May 2022, academics from Skidmore College in New York found that women who exercised in the morning burned more abdominal fat and reduced their blood pressure more than women who exercised in the evening._[14]

• Best time to sleep

While meal and exercise timings are important to your circadian rhythms, sleep surpasses them both. Lack of sleep is known to induce weight gain, and not just because you crave sweet, starchy snacks to keep you going. It reduces your resting metabolic rate, meaning you’re burning fewer calories in a 24-hour period, regardless of your level of activity._[15]

What’s more worrying is that lack of sleep can cause insulin resistance after just five days of reduced shut-eye. People who experience chronic sleep deficits have higher inflammatory markers in their bodies._[16]

So what’s the best time to go to sleep? A UK study_[17] suggests that a bedtime between 10pm and 11pm is the circadian rhythm sweet spot, particularly for cardiovascular health, with the riskiest time after midnight.

But what if you just don’t feel sleepy at 10.30pm? It could be down to your evening routine. Working late, eating late, or scrolling on your phone late at night all have the same effect on the body - they delay the production of melatonin._[18]

The key is to develop a schedule that helps your body synchronise its clock genes with the brain’s central clock. Unwinding earlier in the evening can help, as can getting more natural light in the morning. Sleep experts now advocate that we power down all devices two hours before we expect to go to sleep._[19]

• Can changing your schedule really change your health?

Several studies have found that people who have routines that are not in alignment with their natural body clocks are at greater risk for a variety of health issues.

One recent study found that ‘night owls’ were more sedentary, had lower aerobic fitness levels and burned less fat at rest and while active than early birds in the study. Night owls were also more likely to be insulin-resistant, meaning their muscles required more insulin to be able to get the energy they need._[20]

The key is to give your body clock dependable signals it can work with, week in and week out. So wake up and go to sleep at the same time every day, even on weekends. Have a meal and exercise routine you can set your watch by. It may sound a little rigid, but having a steady, reliable routine really could make optimal health work like clockwork.

If you enjoyed reading this article, you might like What our sleep is telling us about our overall health.

References

[1] https://www.nhs.uk/conditions/jet-lag/
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4436793/
[3] https://www.theguardian.com/lifeandstyle/2019/jan/21/social-jetlag-are-late-nights-and-chaotic-sleep-patterns-making-you-ill
[4] https://www.frontiersin.org/articles/10.3389/fcvm.2019.00084/full
[5] https://ajp.psychiatryonline.org/doi/10.1176/appi.ajp.158.5.704
[6] https://www.nature.com/articles/497S10a
[7] https://www.bbc.co.uk/programmes/articles/2kClp7SPckMyf0GPFn8BGjv/sleep-the-mystery-state
[8] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7147411/#:~:text=Colonic%20motility%20also%20follows%20a,minimal%20activity%20during%20the%20night.
[9] https://www.birmingham.ac.uk/news/2016/vaccinations-are-more-effective-when-administered-in-the-morning
[10] https://hms.harvard.edu/news/late-night-eating-impact
[11] https://www.cambridge.org/core/journals/nutrition-research-reviews/article/physiological-responses-to-food-intake-throughout-the-day/EB78462AB71C926A642283CC765E117F
[12] https://www.sleepfoundation.org/physical-activity/best-time-of-day-to-exercise-for-sleep#:~:text=Aerobic%20exercise%20in%20the%20morning,easier%20to%20fall%20asleep%20early.
[13] https://pubmed.ncbi.nlm.nih.gov/27906554/
[14] https://pubmed.ncbi.nlm.nih.gov/35711313/
[15] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3632337/
[16] https://www.mountsinai.org/about/newsroom/2022/a-consistent-lack-of-sleep-negatively-impacts-immune-stem-cells-increasing-risk-of-inflammatory-disorders-and-heart-disease#:~:text=Chronic%2C%20insufficient%20sleep%20can%20negatively,night%20potentially%20increases%20the%20risk.
[17] https://academic.oup.com/ehjdh/article/2/4/658/6423198
[18] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3925652/
[19] https://www.sleepfoundation.org/how-sleep-works/how-electronics-affect-sleep
[20] https://physoc.onlinelibrary.wiley.com/doi/full/10.1113/EP090613