Sleepless elite ... Margaret Thatcher was said to get by on four hours sleep a night.

Therese Rein once told a journalist that her husband slept about three hours a night.

By this time, Kevin Rudd had already branded himself '24-7 Kevin' and in doing so joined history's long line of short-sleepers: Margaret Thatcher (four hours), Winston Churchill (five), Bill Clinton (five to six), Leonardo Da Vinci (five), Napoleon Bonaparte (three to four), Madonna (four), Silvio Berlusconi (two), P Diddy (less than four), Martha Stewart (two to four) and Donald Trump (three to four).

Some politicians and celebrities have bragged about how little sleep they need - the implication being they are tougher, more productive and more suitable for leadership because of it.

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Is there such a thing as a 'sleepless elite' - a segment of the human population that performs equally well on a few hours sleep?

And if so, is Kevin Rudd a genetic freak, or just sleep-deprived like the rest of us?

Two of Australia's leading sleep experts agree that, like all human behaviours, there is variation in how much sleep people need.

And while genes almost certainly play a role, they say, recent newspaper reports that scientists have discovered a "Thatcher gene" are misleading.

"There are some who need less sleep, but scientists cannot explain completely why," Nick Glozier, Associate Professor of Psychological and Sleep Medicine at the University of Sydney, said.

"In terms of how many people are actually these super short sleepers ... about five per cent of the adult population of Australia sleep like that," he said.

Self-reporting of performance after sleep deprivation is unreliable, which makes it difficult to judge how many people fit into this sleepless elite, Professor Glozier said.

"You can't turn around to pilots and surgeons and say, 'How do you think you're doing after this amount of sleep?', because actually they are probably the worst person to ask," Professor Glozier said.

"For instance, if Kevin Rudd says he thinks he's doing well; he probably isn't the best judge of that."

Others may sleep only four hours at night, but compensate by taking power naps during the day, Professor Glozier said.

"If you look at Maggie Thatcher - she had cat naps."

Professor Leon Lack, a sleep expert at Flinders University in South Australia, said that many of history's short-sleepers probably restricted their REM (Rapid Eye Movement) sleep, which, rather than making a person sleepy often has a "manic" or "energising" effect.

"In rats, for example... it results in increased eating behaviour, increased fighting, increased sexual activity.

"One of the effects of REM sleep loss is people become more emotionally labile, which means more emotionally variable. So they will tend to go through more swings, of exhilaration, but also quicker to anger," Professor Lack said.

As for that genetically-blessed minority who can sleep four hours and be sharp and in a good mood; scientists have only a limited understanding of why they are this way.

Scientists in Germany recently found that one gene, called ABCC9, could partly explain why some people seem able to operate on little sleep, but Professor Glozier said if scientists had really discovered a "Thatcher gene" then managers would surely be recruiting for it.

"You can imagine how valuable that [the "Thatcher gene"] might be. If you're going to run some merchant bank where your traders are expected to work 18 hours... I know what I'd be considering."

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Sleepless elite: quest for the Thatcher gene