Researchers probed the relationship between sleep quality and quantity. (CBC)

People who are able to thrive on just six hours of sleep may have a genetic mutation to thank, researchers say.

In Friday's issue of the journal Science, researchers at the University of California, San Francisco, reported that a mutated gene not found in their relatives seemed to allow a mother and daughter to wake up refreshed by 5 a.m. after going to bed at 11 p.m.

Short-term and chronic disruptions in length of optimal sleep can have serious consequences on physical health, including cancer and endocrine function, as well as cognition and mood, said the study's senior author, neurology Prof. Ying-Hui Fu.

The finding offers a chance to probe the regulation of sleep quality and quantity, but is likely to help people with insomnia, she said.

For most people, eight to 8½ hours of sleep are best, but others function well on six hours.

In the study, the team found mice genetically engineered with the DEC2 mutation also slept less and recovered faster from sleep deprivation compared with normal mice.

When the mutant mice were hooked up to brain-scanning instruments, their brain wave patterns suggested they were well rested even though they had slept less.

The findings point to differences in the sleep needs based on a person's genetic makeup.

Work hours, leisure time activities such as exercising and watching late night TV as well as light and noise levels are also known to affect how much we sleep.

"The question 'How much sleep do we need?' is not only of practical interest for obvious societal reasons, but is also of major importance for understanding sleep function," Hyun Hor and Mehdi Tafti of the Center for Integrative Genomics at the University of Lausanne, Switzerland, wrote in a journal commentary that accompanies the study.

Hor and Tafti said while the mutations is probably rare, the finding offers new approaches to studying the effects of sleep on human health.