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Circadian rhythm: get to know your body clock

Karen Evennett
Article written by Karen Evennett

Date published 16 February 2021

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Understanding your circadian rhythm – your body clock – can help you sleep better, improve your wellbeing and brain health and even your digestion, says Karen Evennett.

Friends and family may marvel at the fact that you manage to wake at the same time every day – even when you forget to set your alarm.

But your ability to do this is one sign that your body clock – your circadian rhythm – is working as nature intended. Just as a flower opens in the morning and closes at night, circadian rhythm dictates that we too should rise with the lark, bursting with energy at the first sign of light.

But daylight isn't the only factor determining the natural sleep-wake cycle. Flowers start to open at daybreak even when they're subjected to constant darkness, and the human body clock is just the same, explains Sammy Margo, a chartered physiotherapist and author of The Good Sleep Guide.

Read on to learn all about your natural rhythm.

What is circadian rhythm?

"Your body is programmed to run like clockwork, without exception. The hormones that regulate your patterns of sleep, hunger, and energy rise and fall at the same times in any 24-hour cycle," Sammy says.

"Nighttime is when bodily systems slow down so that all sorts of deep restorative healing processes can take place. Circadian rhythm doesn't adapt to the fact that you're a night owl, coming to life in the wee hours instead of giving in to sleep.

"If you happen to be active and working at a time when you should be resting, your body simply misses out on its healing processes, and that's why shift workers are unfortunately vulnerable to a litany of health problems."

Lark or night owl?

"Your chronotype – whether you're an owl or a lark – is determined by a subtle difference in the length of something called your PER3: the body clock gene", Sammy explains.

"Larks have a healthy, longer-length PER3. But the shorter PER3 of owls is essentially a design fault. It is at odds with natural circadian rhythm and makes owls want to eat, sleep, work and rest at times when their hormone levels would favour them doing the opposite."

Woman working on laptop late at night

Night owls tend to want to work at times that their hormone levels want them to sleep.

Sleep, brain health and mood

"It is during good-quality overnight sleep that our brains flush out the build-up of toxic beta-amyloid plaques associated with a higher risk of Alzheimer's," says Sammy.

"But regularly missing out on sleep – whether due to your owl gene, shift work, or the fact that you've been travelling across time zones – increases this risk.

"Sleep also governs the appetite-regulating hormones leptin and ghrelin. Missing out can cause the double whammy of increased hunger and a sluggish metabolism that leads to weight gain and obesity, with associated problems such as diabetes, heart disease and cancer.

"There's strong evidence linking low mood with ­poor-quality sleep, too, partly because you're inadvertently subjecting yourself to higher levels of the stress hormone cortisol when you don't get enough shut-eye."

Sleep and the digestive system

Research shows that our gut microbiota (GM, the bacteria in your gut) has its own circadian rhythm, which is also affected by sleep, says Dr Megan Rossi, a registered dietitian and author of Eat Yourself Healthy.

"Just two days of sleep deprivation has been shown to impact our GM, which may explain why not getting enough sleep seems to exacerbate gut symptoms, particularly in people with irritable bowel syndrome (IBS).

"Interestingly, this relationship seems to be bidirectional, meaning that a disturbed GM may also lead to disturbed sleep. But in my clinical practice, I've found that simple dietary changes, such as increasing your daily range and number of plant-based foods, can boost shift workers' GM and, in turn, improve their sleep quality."

Couple going on an early-morning walk in the autumn

6 ways to reset your body clock

Focus on sleep for a happier, healthier circadian rhythm.

Walk it off

Start by waking yourself up for an early-morning walk. An early dose of daylight helps to balance your sleep-wake cycle, and your brain will thank you by preparing you for sleep 16 hours later.

Light up

If your home or workplace is dark, use a lightbox to trick your brain into being more lark-like.

Eat early

Have supper early in the evening to avoid trying to digest food when your metabolism is shutting down.

Be regular

Stick to a regular bedtime. Avoiding late night screen time and dimming the lights will boost melatonin and prepare you for sleep.

Adjust temperature

Keep cool at night (16-18°C) even if you're wide awake – your body temperature should be coolest at 4am.

Nap it

If you're working a night shift have a nap before, and wear dark glasses to travel home afterwards (unless you're driving). You'll be more likely to sleep well even if it isn't at the right time of day for your body clock.

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Karen Evennett

About Karen Evennett

Karen is a freelance health journalist and author/editor of 14 health books. She is a member of the Medical Journalists' Association and her features have appeared in various publications including Woman's Own and the Guardian.