Have you ever noticed how some people bounce out of bed after just a few hours of sleep, while others can barely function without a solid eight hours?

Take Margaret Thatcher, for example. The former British prime minister was known for sleeping just four hours a night . She worked late, rose early, and seemed to thrive on little sleep.

But for most of us, that kind of sleep schedule would be disastrous. We'd be groggy, unfocused, and reaching for sugary snacks and caffeinated drinks by mid-morning.

So why do some people seem to need less sleep than others? It's a question that's fascinated scientists for years. Here's what we know so far.

Natural short sleepers

There is a small group of people who don't need much sleep. We call them natural short sleepers . They can function perfe

See Full Page