Vocabulary: lack of sleep 詞匯: 缺覺

Do you need a lot of sleep? Some famous leaders are thought to have spent little time in the land of Nod so keen they were on their high-powered jobs.

The late Margaret Thatcher earned a reputation for getting by on four hours a night. Tirelessness became part of the former British PM's mystique and her officials had to keep up with her. They could find themselves working on a speech until the small hours of the morning.

Another British head of government, Winston Churchill, survived on four hours a night during the Second World War. But as the BBC reporter Tom de Castella points out, what is less often noted is that he had regular afternoon naps in his pyjamas.

Napoleon Bonaparte was not a man to sleep on the job. When asked how many hours of sleep he needed, the famous French general is said to have replied: "Six for a man, seven for a woman, eight for a fool."

How about ordinary people? Should we try to stifle our yawns and embrace insomnia?

If you want to impress colleagues in the world of business it's certainly something to strive for. High-profile chief executives from Marissa Mayer at Yahoo! to Pepsi's Indra Nooyi get by on four hours a night, while Donald Trump claims to survive on three.

Geraint Anderson, author of City Boy, who worked as an analyst and stockbroker for 12 years, says: "There was a real macho competition in the City about sleep. One of the ways of getting respect was bragging about how little you got".

Experts say that there's nothing wrong with the habit of burning the midnight oil. The only rule is to sleep long enough to feel refreshed when you wake up.

Prof James Horne, at Loughborough's sleep research centre, says that mood is critical. Soldiers high on adrenalin can function on little sleep: "If you're despondent, you tend to sleep more; if you're excited you need less".

Some artists think that sleep deprivation can make them more creative but it might be worth carrying a pillow around. Keith Richards, the Rolling Stones guitarist, once stayed awake for nine days. When fatigue got the better of him, he collapsed and broke his nose.