The science of sleep

Sleep is one of the last mysteries of biology. Photo / Getty Images

Napoleon and Margaret Thatcher needed only four hours, Einstein functioned his genius best with 10. Some of us obsess about it, some try to beat it.

Whether you are a night-owl or an early-bird, we all need it: sleep, beautiful sleep. Do without it and it will soon strike its revenge, wreaking havoc on your brain, damaging your health.

And yet we know so little about it. "It's one of the last mysteries of biology," says Professor Anne Wirz-Justice, a New Zealand-born Swiss academic, a world authority on sleep and human biological rhythms.

"We spend a third of our lives in this strange state, and it must be important because all creatures great and small have sleep."

Wirz-Justice is back in New Zealand as a Hood Fellow of Auckland University, and this week gave the first of four public lectures on the science of sleep. She is a 10-hour-a-night sleeper, when she gets the chance. It's a revelation she knows will prompt gasps or sniggers from others - in modern society, sleeping in is seen as a weakness or deficiency.

"Those of us who like to sleep longer are considered lazy," she says. "But it's not true."

She should know.

* The amount of sleep we need is partly genetically pre-determined.

Traditionally, Western society has deemed that eight hours' sleep is the right prescription for everyone. But it's not as simple as that - and it no longer seems to be true.

A study of American sleep patterns in the 1970s found eight hours was the average, says Wirz-Justice. But 20 years later, the same study found the average had dropped to seven. It's a phenomenon she expects is common elsewhere, including New Zealand.

So how much is enough? "The answer is a very individual one," she says. Genetic and physiological factors come into the equation. Some of us, it seems, are destined to be long sleepers, others short. "There's no judgment about what is better."

Different stages of life determine how much sleep is needed too. Newborn babies spend most of their day asleep. "But as we grow older, [sleep duration] depends on the biological clock as well as the time of year," says Wirz-Justice. "One important point is women would sleep longer than men had they the chance to do so - but they never do."

Another important factor is the time of going to bed. Shift-workers, for instance, who sleep during the day would struggle to slumber more than four or five hours because their core body temperature is on the rise. "The body clock is sending out signals of wakefulness."