Aug. 13 (HealthDay News) -- A lucky few can get by just fine on six hours of sleep, and a new study suggests a genetic mutation might help explain why.

The finding doesn't appear likely to help people with insomnia. Still, it "opens a door" to greater understanding of why people sleep as long as they do, said study co-author Ying-Hui Fu, a professor of neurology at the University of California at San Francisco.

Armed with this research, scientists may be able to eventually develop safe ways to tinker with people's bodies so that they can sleep less, she said. "At the same time, we'll feel fine."

According to Fu, about 5 percent of people get by on six hours or less of sleep a night without any ill effects. "They're perfectly fine, and they don't have a problem," she said. "For them, six hours is like eight hours for me."

For most people, however, eight or 8.5 hours of sleep are best, she said.

"We spend one-third of our life in a state of sleep, and we know that sleep is required. If you deprive any mortal organism of sleep, it will die," Fu said. "But we don't know what is regulating how much we need. That's the bottom line about why this study is exciting."

Fu and her colleagues examined the DNA of a mother and daughter who each get by on about six hours of sleep and compared it to that of other family members. They report their findings in the Aug. 13 online issue of Science.

The researchers found that the women shared a genetic mutation but other members of their family did not. Further research found that mice with the mutation slept less and recovered more quickly after being deprived of sleep.

It's not clear, however, how the mutation actually affects sleep patterns.

Future research could provide more insight into how the mutation works, and Fu said her dream is to find a way to create a drug that would allow people to sleep less.

This could have benefits beyond more wakefulness. Studies have shown that people who sleep an average amount of 30 to 60 minutes below average live the longest, said Dr. Daniel F. Kripke, emeritus professor of psychiatry at the University of California at San Diego.

But genetics are only part of the picture, he said.

"Sleep amounts seem to be determined as much as 50 percent by genetics, and the rest by habits, social and work situations, recreation -- exercise, the Internet and late-night TV -- and environmental factors such as noise and light," he said.

As for the new study, Kripke cautioned that even if the genetic mutation does affect sleep, it's not clear if that helps people who have it. "We do not know if the amount that the people with the variation are sleeping is good or bad for them," he said. "We do not know if the gene effect should be called 'sleep deprivation' or 'enhanced energy.'"

SOURCES: Ying-Hui Fu, Ph.D., professor, neurology, University of California at San Francisco; Daniel F. Kripke, M.D., emeritus professor, psychiatry, University of California at San Diego; Aug. 13, 2009, Science, online