Tina turned on the light. What time was it? Her watch said 2am, but she was not feeling sleepy. So she reached for her phone to see if there were any messages. Then she went to the kitchen and poured herself a large bowl of cerealFoster recommends a light evening meal and warns against late-night snacks.. When she had eaten it, she went back to bed with her tablet and started looking for something to watch. Another episode of Friends - why not?

According to Russell Foster, head of Oxford University's Sleep and CircadianThe term is made up of two Latin words meaning approximately and a day. Neuroscience Institute, these are all the worst things she could do. His new book The New Science of the Body Clock, and How It Can Revolutionise Your Sleep and Health explains why.

All of us have a body clock. It controls every aspect of our lives in a 24-hour daily - or circadian - rhythm. Whether we function efficiently depends largely on our ability to work in harmony with this cycle.

"We need the correct materials in the right place, in the right amount, at the right time of day," Foster writes. "Thousands of genes must be switched on and off in a specific order."

"Proteins, enzymes, fats, carbohydrates, hormones and other compounds have to be absorbed, broken down, metabolised and produced at a precise time for growth, reproduction, metabolism, movement, memory formation, defence and tissue repair... without precise regulation by an internal clock, our entire system would be in chaos."

Night is above all a time for repair and recovery. Medicines such as aspirin work much better if taken before bed. Children with cancer have been found to do five times better if given chemotherapy in the evening rather than in the morning.

Increased sleep can counter obesity and diabetes. People deprived of it tend to eat more because their bodies produce extra ghrelin - the hormone that makes us feel hungry. A study found that sleeping for an extra hour and a quarter helped overweight people consume up to 500 fewer calories a day.

Today, unfortunately, we live in a 24/7 society. It encourages the idea that we can do anything whenever we want to, regardless of our body clocks. It also depends on many people working through the nightIn the UK, three million people do night shifts. to make that possible. But 97% of night workers never adapt to this routine, and never get enough sleep.

The consequences are alarming. Sleep loss has been linked to hundreds of thousands of road accidents, as well as major disasters such as those at ChernobylThe disaster, in 1986, involved a meltdown at a nuclear plant in Ukraine. and BhopalA gas leak from a pesticide plant in the Indian city killed over 2,000 people.. Men who work at night are six times more likely to separate from their wives in the first five years of marriage.

Night workers are also more vulnerable to disease since our white blood cells - which attack invaders - are at their most active during the day.

But according to another book, Generation Sleepless, the most sleep-deprived people of all are teenagers. They need more sleep than adults - nine to ten hoursA study found that only 30% of secondary school pupils managed this on most nights. - yet in the US they average just six and a half. Addiction to smartphones is a major factor since they stimulate the brain instead of allowing it to slow down into sleep mode. 

Yes: Our bodies work on a timetable and need time to recover and regenerate. If we do not get enough sleep, all manner of things start to go wrong. We are also likely to make dangerously bad decisions.

No: It is just one of several factors. Eating properly, taking exercise and avoiding smoking and too much alcohol are equally important. Many high-functioning people get by on very little sleep.

Or... If it is, nature has got things badly wrong. There is not much point in life if you spend a large proportion of it unconscious. Our human destiny is to achieve things, not just to snooze.