The body clock's most obvious function is to tell you when to get up and when to go to bed
Are you a night owl who has to get up at the crack of dawn for work, leaving you constantly sleep-deprived and stressed?
Or a natural lark who works evenings and nights?
An out-of-sync body clock can raise your risk of cancer, heart disease and type 2 diabetes, and lead to weight gain
, according to new research.
It was reported last month that women who sleep in bedrooms with more light were more likely to be obese
- possibly because bright light at night confuses the body clock, which in turn may affect appetite and metabolism.
And leading sleep scientists have warned that the demands of our increasingly 24-hour society mean we're constantly over-riding our body clocks.
'Many people don't even realise they're sleep-deprived,' says Russell Foster, professor of circadian neuroscience at Oxford University.
'But if you need an alarm clock to wake in the morning, you probably don't get enough sleep - and are out of sync with your body clock.'
So, what does the body clock do and why is it so important to health?
Here we reveal the latest on this still emerging science ...