Have you ever noticed that when the clocks change in spring and autumn, adjusting to the time change can leave you out of sorts for days? It’s not your imagination. There’s a good chance you’re out of sync with your body clock. And, thanks to recent research, we now know that living out of step with your natural rhythm can affect your health and wellbeing both now and in the future. In this guide we’ll show you how to reset your body clock so you can stay in sync with your body.

What is the body clock?

The body clock, also known as the circadian rhythm, is a daily cycle of biological processes that exists in animals and plants. “It’s your body clock that cranks up your metabolism , raises your body temperature when you need to be alert and winds it down when it’s time to rest,” explains Russell Foster, Head of the Nuffield Laboratory of Ophthalmology and the Sleep and Circadian Neuroscience Institute.

When exposed to light early in the morning, the suprachiasmatic nucleus, a cluster of cells in the hypothalamus at the base of your brain, sends signals to stop the production of the sleepy hormone, melatonin. It then releases cortisol to wake your body’s metabolic processes. In the evening, as light levels fall, the process happens in reverse.

Researchers at Oxford University recently discovered there is a separate sensor in your eyes that attracts light specifically to regulate the body clock. And we now know there is a body clock gene in every cell of your body. It’s these cells that directly influence the rhythms of your heart, lungs, liver and other organs.

“The hypothalamus acts as the conductor of an orchestra, keeping them all in time,” says Dr Victoria Revell, chronobiologist at the University of Surrey and a director for the Society for Light Treatment and Biological Rhythms.

What happens when your body clock changes?

The body clock evolved to sync with the earth’s 24-hour light-dark cycle. But now we stay up later and later. On average, we sleep for two hours less than we did in 1960, and, as a result, the production of melatonin can be delayed. If you’re out of sync with your body clock, melatonin levels can still be high when you wake,” explains Dr Revell.

That means your body may still be in sleep mode when you’re driving to work in the morning. At the end of the day, an out-of-sync body clock can also stop you falling asleep.

Even a slight shift in your daily sleep-wake routine can throw you out of sync. Many of your genes known as ‘rhythmic genes’, are controlled by your body clock. In a study at the University of Surrey, a group of volunteers had their sleep cycle delayed by three or four hours on consecutive nights until they were awake all night and asleep during the day. Researchers found that 97% of rhythmic genes were affected by this body clock shift.

Miss out on an hour’s sleep, even if it’s just for a week after the clocks change, and you could potentially affect the activity of more than 300 genes, including those that control your immune system and your response to stress. In the longer term, scientists believe that resisting the natural cycle can have serious consequences for our health.
“Forcing your body to be active at a time it should be asleep triggers a stress response that lowers your immune system and puts a strain on your heart,” explains Professor Foster.

Living out of sync with your body clock could even affect how you age, according to scientists at the University of California, by leaving stem cells more vulnerable to DNA damage.

It can also take its toll on mood. Scienists from Stanford University found that the body clocks of people suffering depression were so out of sync with their daily lives, it was as if they were living in a different time zone. Although it’s not known why, it’s thought to be a side effect of disrupted genes.

“Changing pathways of gene expression or how the coding in your genes is read has a huge effect throughout the body,” says Dr Revell.

Are you an early riser or a night owl?

Convinced you’re a natural night owl? Staying up late is more likely to be a habit than an innate drive. Scientists at the University of Surrey have discovered a gene, Period 3, that determines whether you’re a night owl or a lark. Period 3 comes in a long and short version, and we all get two copies of it, one from our mother and one from our father.

Around 10% of the population has two long versions of the gene and they tend to be very early risers, while between 10 and 15% has two short copies, which makes them night owls.

The rest of the population has both long and short, which means that their daily habits determine whether they become a lark or owl. A group of night owls camped outdoors for a week with no electric lights or torches, for a recent Colorado University study. Within a week their body clocks had shifted. The key was their increased exposure to sunlight, which was around 400% more than normal.

How to reset your body clock

  1. Get outside first thing
    Light exposure is crucial for regulating your body clock, especially early in the day. Lux is the measurement of light falling on a surface. At home or work, you’re exposed to around 50 lux. Outside, you get between 10,000 and 25,000 lux. So, make time for a walk early in the day. “I think of it as a photon (light) shower for the brain,” says Oxford University professor Russell Foster. Women who did this regularly had lower BMIs than those that weren’t exposed to morning light, according to a study by the Northwestern University Feinberg School of Medicine in the US.
  2. Stick to regular mealtimes
    We may have a ‘feeding clock’ that can override clock, keeping us awake to look for food when we haven’t eaten, say Harvard University scientists. Some experts suggest fasting could push your body clock later. This is useful for overcoming jet lag, but to keep in sync, stick to regular mealtimes. Studies by the University of Surrey show the body becomes less sensitive to insulin and less efficient at processing fat towards the end of the day, so keep your evening meal light.
  3. Read a book at bedtime
    Late-night screen time can disrupt your body clock, according to a study by Brigham and Women’s Hospital (BHW) in the US. “Participants reading an e-book (on an iPad) took longer to fall asleep, had reduced evening sleepiness, melatonin secretion and next morning alertness, and later timing of their circadian clock than when reading a printed book,” says study researcher, neuroscientist Dr Anne-Marie Chang. Light wavelengths have different colours, and the sensors in the eyes that grab light for the body clock are particularly receptive to blue light, emitted by daylight but also computer screens.
  4. Sleep in the dark
    Even a dim light in your bedroom, from a smartphone or a TV standby button, can inhibit the release of the sleep hormone melatonin, pushing your body clock later. It may also affect your weight. Oxford University scientists studied 113,000 British women with an average age of 47 and found that those with the largest waistlines slept with enough light in their bedrooms to see the outline of furniture across the room at night. If you can’t block out all light, try sleeping with an eye mask.
  5. Skip lie-ins at the weekend
    Sleeping late at weekends puts you at risk of ‘social jet lag’ – that groggy feeling on a Monday morning. For every hour of social jet lag, the risk of being overweight or obese raises about 33%, according to research from the University of Munich. If you’ve had a late night at the weekend, have a short nap after lunch to boost energy levels instead.

Health benefits of resetting your body clock

The link between the body clock, insulin, and how it affects diabetes and weight gain, is being investigated by scientists. Disruption to your body clock reduces the ability of your pancreas to make insulin, raising the risk of diabetes, according to researchers at UT Southwestern Medical Centre in the US.

Your sensitivity to insulin is controlled by your body clock, say researchers at Vanderbilt University in the US, suggesting that when you eat could be just as important as what you eat if you want to stay slim. It may explain why only eating during your most active eight hours will keep you slimmer, as found by a University of California study.

Dieters who ate their biggest meal at lunchtime lost 25% more weight than people who ate the same amount of calories but had their biggest meal in the evening, in a study by Brigham and Women’s Hospital (BWH) in the US.

“During the body’s resting phase in the late evening and night-time, food is more likely to be stored as fat rather than converted to energy,” says Professor Foster. “The body isn’t as efficient at processing fat at night,” he says, “and the glucose-insulin response is impaired.”

Getting out of sync with your body clock also makes you hungry. Scientists at the University of Chicago found that after only two nights of having two or three hours’ less sleep than normal, the body produces 15% more ghrelin, an appetite-boosting hormone, and 15% less leptin, the ‘full-up’ hormone.

When to adjust your body clock

Part of the reason we can struggle to adjust to British Summer Time (BST) is that we tend to stay up later and sleep later at weekends, pushing our body clocks forward. This means we find it hard to fall asleep at our usual bedtime on the Sunday evening of clock change day, which is technically an hour earlier. “It’s the equivalent of flying two or three time zones eastwards,” says Dr Revell.

The good news is that most people adjust to BST within a week or so. To ease the transition, try bringing your sleep and wake times forward by 20 minutes daily for the three days leading up to the clock change. And try getting some bright light early in the morning to boost alertness and mood – a really enjoyable way to improve your health!

Body clock phases

Have more energy by organising your day around what your body is naturally doing

  • 6am to 9am
: Melatonin production ceases. This is an optimum time to wake and a poor time to exercise.
  • 9am to 12pm: 
Stress hormone cortisol peaks. Maximum alertness – best time to work. Short-term memory at its best.
  • 12pm to 3pm: 
Increased gastric activity – either because you have just eaten or your body clock is telling you it’s time to. Post-lunchtime dip in alertness. Peak time for road accident fatalities is at 2pm.
  • 3pm to 6pm
: Core body temperature peaks. Best heart and lung capacity. Muscles are six per cent stronger than at other times. Best time for physical exercise.
  • 6pm to 9pm: 
Intuitive thinking is improved. Digestion of big meals is less effective. The liver, however, is more able to process alcohol than at lunchtime.
  • 9pm to 12am: 
Dip in natural light stimulates melatonin production. Core body temperature drops. Optimum time for bed.
  • 12am to 3am
: Levels of melatonin peak. Bowls shut down for the night. Attention span at a minimum. Brain organises and consolidates memories.
  • 3am to 6am
: Core temperature low while body repair work occurs. Severe asthma attacks more common. Natural births tend to occur most.