Some people may naturally need only four to six hours of sleep each night and still feel energetic during the day. Scientists believe rare genetic variations may explain why these individuals can function well with significantly less sleep than most adults. Aimee Pugh Bernard, an immunology professor at the University of Colorado, typically goes to bed around 10 pm and wakes up at approximately 4:30 am. Despite sometimes sleeping for only five hours, she says she usually feels alert and productive. Her father and brother reportedly share a similar sleep pattern. Most adults aged 26 to 64 need around seven to nine hours of sleep in every 24-hour period, according to the US National Sleep Foundation’s evidence review. Bernard discovered that she likely has a rare genetic variation associated with a condition known as familial natural short sleep (FNSS). People with this inherited condition tend to wake up early and may naturally sleep between four and six-and-a-half hours without experiencing the usual effects of sleep deprivation. Researchers have identified several genetic mutations linked to FNSS, although the precise biological mechanisms are still being studied. Scientists are investigating whether these variations may help protect short sleepers from some consequences of insufficient sleep, including memory problems. Experiments involving mice found that certain FNSS-related genetic variants were associated with fewer memory deficits and a lower likelihood of developing Alzheimer’s-like disease. However, these findings in animals do not establish the same protective effects in humans. A 2014 study involving fraternal twins also found that the twin carrying a short-sleep mutation slept about an hour less than his sibling. During a prolonged period of sleep deprivation, the carrier experienced fewer performance lapses. Researchers observed that despite sleeping less, the carrier twin obtained nearly the same amount of non-REM sleep, including deep sleep. Scientists say these findings may eventually help explain how sleep duration varies between individuals. However, naturally short sleepers are rare, and most people should not assume that sleeping only four or five hours is sufficient.

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