Most adults need seven to nine hours of sleep per night, but a small group feels rested after four to five hours. Scientists link this trait to rare genetic mutations that may make sleep more efficient.
One example is immunologist Aimee Pugh Bernard. She usually falls asleep around 10:00 p.m. and wakes up at 4:30 a.m. After approximately five hours of sleep, she feels alert, exercises and carries out her work duties. In 2019, Bernard discovered that she carries a rare mutation linked to familial natural short sleep syndrome.
What the experiments show
People with this syndrome can sleep between four and six and a half hours without experiencing the usual daytime sleepiness. Researchers have already discovered several mutations associated with the trait, but the exact mechanism behind their effects remains unclear.
In experiments with mice, carriers of some of the mutations slept less but showed greater resilience to memory impairment. In one of the studies, the animals were also less likely to develop the murine form of Alzheimer's disease.
Another study compared fraternal twins, one of whom carried a mutation linked to short sleep. He slept approximately one hour less than his brother. After 38 hours without sleep, he made about 40% fewer errors while performing tasks. He retained almost the same amount of non-REM sleep, including deep sleep, suggesting that he may use his rest time more efficiently.
Genetics Does Not Explain Everything
According to researchers' estimates, genetic factors explain between 30% and 65% of the differences in sleep duration. An analysis of data from nearly 650,000 adults identified around 244 regions of the genome associated with this measure.
Most common genetic variants have a small effect. Each of them changes sleep duration by an average of about one minute, but their combined impact can reach approximately 20 minutes. A genetic predisposition to short sleep is also associated with various health indicators, including insomnia, fatigue, depressive symptoms, attention-deficit/hyperactivity disorder and type 2 diabetes.
Four Hours of Sleep Is Not a Universal Norm
The research does not provide grounds for most people to restrict their sleep. In healthy adults who sleep for four to six hours, performance on cognitive tasks gradually deteriorates, even though the participants themselves rate their sleepiness as mild.
Therefore, feeling alert is not sufficient evidence that the body is not suffering from sleep deprivation. Scientists continue to study the genetic mechanisms to determine which people are genuinely resilient to short sleep and whether this knowledge could help in developing approaches to treat sleep disorders.
Sources: healthnews.obozrevatel.com, bbc.com