Can some people thrive on only 4 hours of sleep every single night? It's rare, but neuroscientist Dr. Ying-Hui Fu says it can happen.

Fu is a neurology professor at the University of California, San Francisco. In her own words, during a recent Reddit AMA, she said the importance of sleep is secondary only to water and air. Her belief in the importance of sleep has led Fu to devote more than 20 years to researching sleep and genetics.

During her studies at UCSF, Fu discovered what she terms "short-sleepers" — people who naturally wake up after only 4 to 6 hours of sleep and have enough energy to carry them throughout the day. Such sleep patterns aren't normal at all — and Fu wanted to learn why the rules seemed to not apply to a handful of people.

In 2009, Fu connected with a patient in the sleep program who came in complaining of a bizarre sleep schedule. Even though the patient went to bed between 10 p.m. and midnight, she would wake up completely alert every morning at 4 a.m. The woman reported feeling refreshed and energetic for the rest of the day. Members of the woman's extended family shared the same schedule.

Fu was perplexed. As a sleep scientist, this flew in the face of everything she knew about restful sleep.

A Regular 8 Hours

People who sleep less than the recommended 7 to 8 hours per night are more likely to suffer from chronic conditions like cardiovascular disease, obesity, depression, diabetes and even dementia, Fu and other experts say.

Fu's research lab found that people who averaged 4 hours of sleep were 4 times more likely to catch colds.

"Sleep is very important," Fu explains. "You need a minimum of 7 hours, and likely you need more. Some people may need up to 12 hours."

Determined to find out more, Fu mapped the genomes of this unusual patient, along with her extended family, and found something shocking: The family members who felt well-rested after 4 hours of sleep all shared a mutation of the gene DEC2. This gene mutation was not present in the family members who slept longer.

“The subject was so excited. All her life doctors had been telling her she was crazy or depressed," Fu says.

Fu and her sleep team published their findings in the April 2009 issue of the journal Science. The defect, Fu says, impacts a very small but diverse segment of the population.

"I get e-mails from people all over the world who are short sleepers," Fu says. "All races, all kinds of people. But it's easier to study in the United States because it's harder to transfer DNA across countries."

So far, Fu has discovered only a few hundred people with the CED2 gene mutation. Other mutations have shown to cause shortened sleep, but a lack of funding has impeded researchers from studying more.

Trained vs. Natural Sleep

By Fu's estimation, thousands of people could be affected by shortened sleep genes. But just because some people are capable of getting by on 4 to 6 hours of sleep doesn't mean everybody should try.

In Fu's experience, natural short sleepers are energetic and rarely get sick. People who try to train themselves to be short sleepers, on the other hand, are much more likely to suffer adverse health effects since they need to be getting more sleep and are choosing to go without.

So what does Fu recommend for people who are thinking about living on less sleep? In a word: Don't.

"We only study people who are naturally short sleepers, who were born this way," says Fu. "When you don't sleep, your immune system is weaker. You're much more likely to get sick."

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