Your circadian rhythm regulates when your body needs sleep, food and activity. Angela Tufvesson investigates why good health depends on staying in balance with your sleep-wake cycle


Do you struggle to get up each morning, taunted by ‘morning people’ who just seem so damn perky the minute they roll out of bed? Or have your friends labelled you a piker because you never stay out past midnight?

Whatever your Achilles heal, put your mind at ease as your sleep patterns have little to do with your staying power (or lack thereof) and everything to do with your physiological makeup.

Like clockwork
The biological clock situated in a central area of the brain called the hypothalamus regulates the timing of many rhythms in the body. Functions such as hormonal secretions, heart rate, body temperature and feelings of sleepiness and alertness vary regularly with peaks and troughs across the day. These regular rhythms are called circadian (‘circa’ meaning about, ‘dian’ meaning day) rhythms.

“Timing of events in the body is important because a particular hormone that is released needs to be released in relation to other events in the body,” says Associate Professor Shantha M. Wilson Rajaratnam from the School of Psychology and Psychiatry at Monash University. “Processes need to have some kind of internal synchrony – things need to run like a well conducted orchestra.”

Our body clock operates on a 24-hour cycle that adapts our bodies to the light-dark pattern of day and night. It’s why we need to eat multiple meals a day, as well as why we sleep at night and are awake during daylight hours.

“Our circadian rhythm or body clock plays an important role in the timing of our sleep period,” says Dr Helen Wright from the School of Psychology at Flinders University. “For most people their body clock is timed so that they can fall asleep easily about 11pm and wake at 7am.”
But this isn’t always the case. Night owls – those who party through the night and sleep until lunchtime – are programmed to hit the sack at 1am or 2am, while morning larks – sprightly morning people who crash early – are wired for a 9pm bedtime.

“There are considerable individual differences in the timing of these processes and these are also reflected in the body temperature (melatonin) rhythm,” Prof Rajaratnam says.
While we don’t completely understand why there are differences between individuals, new research suggests our genes may play a major role in determining the running of our body clocks.

“We’ve begun to understand that these differences are strongly reflected in internal physiology and there may be genetic differences that may account for some of these differences,” Prof Rajaratnam says. “Different genotypes can result in an alteration of timing of these events in people.”
Gender may also play a role, with some studies showing female circadian rhythms are influenced by different stages of the menstrual cycle, reflected in changes in body temperature and the sleep-wake cycle.

Interestingly, our body clocks slow down and speed up at different stages of our lives. Just as we move our clocks forward for daylight saving, so too do teenagers at the onset of puberty, staying up till all hours and annoying their parents.

And at the opposite end of the spectrum, the over 55s have reprogrammed their clocks to suit the ‘early to rise, early to bed’ phenomenon – it’s why a 16-year-old and a 60-year-old virtually live in different time zones.

Upsetting the rhythm
So what happens when we ignore our body clock? It’s akin to ignoring your watch and turning up to appointments at the wrong time – your body becomes stressed, which can lead to a number of serious health conditions.

Upsetting our internal synchrony means the careful rhythm with which our body operates is thrown out, and we’re unable to perform at our best. And because circadian rhythms control the release and timing of hormones, mood disorders and sleep disruption may result.
Weight gain is also a common symptom, as when we’re not in a regular sleep pattern, hormones that regulate whether we feel full or hungry become out of whack as all of our normal cues for eating are disturbed.

For those who must upset their internal rhythm due to work or family reasons, the health consequences are potentially a lot more serious.
“If we look at shift workers, they live at odds with their circadian rhythms,” Prof Rajaratnam says. “Some of the health conditions documented to be associated with shift work include an increased risk of cardiovascular disease, diabetes, a number of psychological and mood disturbances, reproductive problems and most recently the evidence related to cancer was evaluated. The World Health Organisation (WHO) reported that shift work was a probable carcinogen.”

Similarly, frequent flyers are at risk of health problems as they travel across time zones. To a lesser extent, so too are office workers on the 9am to 5pmshift if their optimal bedtime is well past midnight.

“If you are unable to fall asleep until 2am but have to get up for work at 7am, you will get insufficient sleep – only about five hours,” Dr Wright says. “Over a week this can really affect your mental and physical functioning.”

Know your time zone
To reduce your risk of disease and be at your best, the first step is to work out which time zone your body ‘lives’ in.

“Try and understand your own internal rhythm that isn’t influenced by caffeine, heavy meals or exercise close to the time you go to sleep – take out all of those things that upset your normal sleep cycle,” Prof Rajaratnam says. “Get an understanding of what your normal sleep cycle is like.”
Work out if you’re naturally an owl or a lark, and if you can, customise your work, family and social commitments to suit. But if this isn’t practical – the average workplace is rather ‘sleepist’ – solutions are at hand.
Most importantly, commit to consistent waking and sleeping times and when you rise each morning be sure to open your curtains to let the sunlight flood in.

For most people, the circadian rhythm is a little over 24-hours and needs to be reset every morning by exposing our eyes to light. To shift your body clock, follow a careful pattern of light exposure to try and bring your circadian rhythms either earlier or later in time.
“If you’re a late person and you want to bring that earlier, avoid evening light – have dim light – and have bright light in the morning,” Prof Rajaratnam says. “The reverse applies if you can’t stay awake at night – dim light in the morning and bright light in the evening.”
Sticking to a sleep schedule and not giving in to the dreaded ‘sleep debt’ is crucial.
“Catching up on sleep by sleeping in on weekends only exacerbates the problem,” Dr Wright says. “This causes a delay of the body clock even more as you are not getting that morning light exposure.”
In serious cases, light treatment may be prescribed, where a box emits blue light as the brain is most sensitive to this type of shortwave length light.
In any case, understanding your body clock and respecting its needs will go a long way to improving your health. And remember, you’re not lazy if you can’t get up in the morning or a piker if you hit the hay early – it’s your biology talking.