How important is our body clock?

Do we have a built in body clock? If so, what triggers it? Does it influence our sleep? And what are the health implications?

Do we have a built in body clock?

More night shift workers, people driving at night and people working through a 24 hour cycle experience accidents (pro rata) compared with their day time counterparts. And our ability to perform maths calculations or other intellectual tasks between 4 and 6 o’clock in the morning is worse than if we had drunk enough whiskies to be legally drunk.

That’s because, like animals and plants, we have a built in body clock – which probably evolved to help our bodies make the most productive use of daytime for activity and night time for sleeping. When our body clock is upset, for instance as a result of a long distance flight to a different time zone, we often experience physical and mental symptoms – typically described as jet lag.

What triggers our body clock?

Light and darkness are the two main triggers. Over many thousands of years our bodies have evolved to respond to the cycle of day and night, light and darkness.

Does it influence our sleep?

Yes. That’s why people who experience difficulty sleeping are sometimes advised to spend time outside during the day (to provide the light cues your body needs to reinforce that this is the time to be awake). And then to avoid blue light (from computer screens, tablets and mobiles) before sleeping and to sleep in a room which is as dark as possible (to provide the darkness cues your body needs to reinforce that this is the time to go to sleep). Some sleep problems seem to be due to modern lighting and communications technology (e.g. generating increased blue light from computer and mobile screens), long haul flights and night shift work – all of which can potentially confuse our natural body clocks.  

What are the health implications?

The health implications are now beginning to be recognised and researched. For example Oxford University has appointed a Professor of Circadian Neuroscience and there is growing interest in ‘chronotherapy’.  Clinical trials suggest that administering medication for cancer at the time it is most likely to be tolerated within the circadian cycle has two advantages. Patients tend to experience less severe side effects and the medication usually achieves the best anti tumour activity.  

Prevention is better than cure. So, can we use what we know of our natural body clocks to help stay healthy and reduce the risk of falling ill? Here’s what the research so far suggests:

Disruption to our body clock and consequent sleep loss:

  • Is likely to increase the risk of breast cancer (as seen in studies of nurses and flight attendants).
  • May increase the risk of prostate cancer (as seen in studies of airline pilots).

NB One of the authors of the study above has appeared as an expert witness in cases relating to the effects of shift work on health and safety, so there’s a possible conflict of interest to be aware of. Having said this, a number of separate studies have confirmed the risks arising from lack of or disrupted sleep.

  • Is a risk factor for diabetes and hypertension  (as in a study of 26,000 retired shift workers in China). A 2009 systematic review of research in this field concluded. ‘Quantity and quality of sleep consistently and significantly predict the risk of the development of type 2 diabetes.’
  • May even increase the risk of putting on weight and obesity (as in a 16 year study of over 60,000 nurses)

Might other factors be at work?

A number of other factors might influence research findings on sleep. For example some medical conditions and some medication may limit the ability to sleep. And people with lower socio economic status may be more vulnerable, for instance because they may have to work longer and more anti social hours and may sleep in noisier environments. However, many studies now try to take account of other possible factors (called ‘confounders’ by researchers) and often find lack of sleep has an independent effect in its own right.

A U shaped effect?

Some studies have suggested that too much sleep as well as too little can indicate health risks (what researchers call a u shaped effect). This may apply to:

7 – 8 hours of sleep seems to be the healthiest amount, with less than 6 hours sleep and more than 9 hours each suggesting increased health risks.


We each have a natural body clock. So work with it to get an optimum 7 – 8 hours sleep per night. To give your body clock the cues it needs:

  • Spend time outside during natural daylight hours.
  • Avoid blue light before sleeping and background lights while asleep.
  • If possible avoid night shift work or work that induces regular jet lag.

This is likely to reduce the risk of diabetes, breast cancer and obesity – and may reduce the risk of heart disease and prostate cancer. 

Michael Baber

Published 16 May 2014, Review date February 2017

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