People who only need 4 hours of sleep and how genetics explains it

Image source, Getty ImagesImage caption, For some people, a few hours of sleep is enough. By Amanda RuggeriBBC Future*Published9 minutesReading time: 9 minFor as long as she can remember, Aimee Pugh Bernard has not needed much sleep. Currently, she usually goes to bed around 10:00 pm and wakes up around 4:30 am. "I'm fully awake. I can't stay in bed," she says. Sometimes, Bernard — a professor of Immunology at the University of Colorado, United States — cannot fall asleep right away. In those cases, she sleeps barely five hours. The most surprising thing is that, the next day, Bernard usually feels full of energy. She walks her dog, does an intense one-hour workout at the gym, and completes an hour and a half of work before 8:00 am. Her friends are amazed at her ability to get so much done on so little sleep. However, in her family this is normal: both her father and her brother are the same. Most of us, of course, need more. According to the most recent review of the scientific evidence by the National Sleep Foundation of the United States, an average adult between 26 and 64 years old requires between seven and nine hours of sleep per 24 hours. The reason for such a wide variation in each person's sleep needs has long been a mystery. Skip Most read and continue readingMost readEnd of Most readNevertheless, in recent years, scientists have identified various ways in which genetics influences this aspect. From rare mutations — like the one Bernard has — to hundreds of much more common variants, there are explanations for why some people can function well on very little sleep. In the future, these findings could help protect those who do not manage to sleep enough, helping them avoid some of the usual consequences of sleep deprivation. The first cluesIn 2019, Bernard discovered the possible cause of her particular sleep-related "superpower." A research team at the University of California, San Francisco, USA, identified a genetic mutation linked to sleep duration in humans. Although people carrying this mutation went to bed at fairly conventional hours, they woke up very early, generally sleeping between four and six and a half hours each night. After sending a blood sample to the research team, Bernard learned that she was one of those people. This rare, hereditary condition is called "familial natural short sleep" (FNSS). Since then, other mutations associated with FNSS have been identified. One of the biggest mysteries surrounding FNSS is that those who have it seem to be "fine" despite sleeping so little, says the team's principal investigator, molecular biologist Ying-Hui Fu. The exact reasons are still being studied. There are fascinating indications that the genetic variations linked to FNSS not only cause a reduced need for sleep, but also protect those who carry them from the consequences of lack of rest, such as, for example, memory impairment. Image source, Getty ImagesImage caption, A test revealed that mice with some sleep-linked variants were less likely to develop a version of Alzheimer's disease. In an experiment conducted in 2019 under Fu's direction, a mutation related to FNSS was introduced into mice. The team observed that the mice carrying this variant not only slept less, but also appeared to be protected against memory deficits. Another test revealed that mice with some of these variants were less likely to develop a version of Alzheimer's disease in this species. In 2014, an international research team studied a pair of dizygotic twins, one of whom had a mutation associated with short sleep, while the other did not. It was observed that the carrier twin habitually slept about an hour less than his brother. They also found that, when both were kept continuously awake for 38 hours, the carrier twin had about 40% fewer performance failures than the other twin. The researchers also found interesting differences in the way the two twins slept. Although the carrier twin slept less time, his amount of non-REM sleep — which includes slow-wave or "deep" sleep — was practically the same as his brother's. This could mean that, in some way, he was getting greater benefits from the time he spent sleeping. Pharmaceutical dreamsHowever, research in this field continues, and it is essential, says Fu. In recent years, interest has grown in how our knowledge of these genetic variations could be harnessed to help people. In the pharmaceutical industry, there is hope that, one day, discoveries about people who need little sleep could lead to the development of drugs to treat sleep disorders or, for example, help military personnel perform on fewer hours of sleep. To do this, scientists not only need to be clear about whether these variants protect short sleepers from negative consequences, but also understand exactly how they do it. Without this information, there is a risk of creating a drug with unexpected side effects."You have to understand how it works," says Fu. "You wouldn't want to sleep less and, after five, ten or 20 years, end up developing Alzheimer's, Parkinson's or cancer." Image source, Getty ImagesImage caption, Thomas Edison, one of the inventors of the light bulb, said he never slept more than four hours. While the genetic mutations associated with FNSS are one of the most extreme and fascinating examples, they represent only a small part of the genetic factors that can determine the duration of our sleep. In general, it is estimated that our sleep duration has a heritability of between 30% and 65%; this means that up to 65% of the differences in sleep duration between people can be explained by genetics. To date, several hundred regions in the genome that influence sleep duration have been identified. A recent analysis, which examined data from nearly 650,000 adults, identified around 244 of these regions. (This research has not yet been published and is currently in preprint). According to the study's lead author, geneticist Isabelle Austin-Zimmerman of King's College London, if we look at each of these common mutations individually, we see that they are only associated with a difference of about one minute in sleep duration. However, when combined, their effects can accumulate. Austin-Zimmerman points out that, in an average person, genetic differences could explain a variation of about 20 minutes in sleep duration. However, there is still not much research on which of these more frequent variants might protect people from the effects of sleeping little. Even so, a recent study led by Chiara Petrosellini, an academic clinical obstetrician and gynecologist at University College London, found indications of one of these variants. The research team analyzed the genetics of 343 women with bipolar disorder who had given birth. Their genetic profile was evaluated to determine the probability that they were people who need little sleep, based on the presence of mutations that are suspected to be involved in this trait. Those with a greater predisposition to needing little sleep had half the risk of developing postpartum psychosis compared to women with a lower predisposition to this trait. A similar trend was observed in the case of insomnia. Although more studies are needed, the researchers suggest that these people may have developed, over their lifetime, a greater tolerance to sleep disruption. This could be mitigating the impact that lack of sleep — common in the postnatal period — has on their mood. Image source, Getty ImagesImage caption, A study revealed that genetic variants associated with shorter sleep duration carry a higher risk of suffering insomnia and experiencing tiredness. However, unfortunately, having a genetic predisposition to sleep little is not always beneficial. In fact, research conducted by Austin-Zimmerman and her team in a much larger population (not limited to mothers with bipolar disorder) revealed that, in general, genetic variants associated with shorter sleep duration carry a higher risk of suffering insomnia and experiencing tiredness. They were also linked to various physical and mental health problems, including ADHD, depressive symptoms and type 2 diabetes. This does not necessarily mean that sleeping little — or having a predisposition to do so — is the cause of these conditions. But it does imply that a genetic predisposition to sleep little does not always protect against these risks. The illusion of being fineTo complicate matters further, even those of us who believe we function properly on little sleep are not always the best judges of our own situation. One study, for example, revealed that when healthy adults had their time in bed limited to only four or six hours per night, their performance on various cognitive tests progressively worsened. However, after two weeks, the participants said they felt only "slightly" sleepy."Your ability deteriorates more and more, but at the same time, you become less and less aware of that deterioration," explains Hans van Dongen, a sleep researcher at the Sleep and Performance Research Center at Washington State University and co-author of the study. It is true that many people need fewer hours of sleep than others. Other research, conducted by Van Dongen himself, has shown that there are individuals more resistant to sleep deprivation. However, this means that understanding such differences is more complex than simply asking how many hours someone sleeps or how they feel the next day. In the long term, genetic findings like those of Austin-Zimmerman and Fu could help identify people who truly function well on little sleep. They could also serve to distinguish those who, although they feel fine, are actually at greater risk of suffering a decline in their abilities. Over time, it is hoped that these discoveries will lead to the development of drugs that help short sleepers strengthen their resistance to sleep deprivation. Image source, Getty ImagesImage caption, The hope is to develop drugs to treat sleep disorders or, for example, help military personnel perform on fewer hours of sleepMeanwhile, these findings can help people understand why they sleep the way they do. In Bernard's case, knowing that she carried one of the genetic variants associated with natural short sleep helped relieve some pressure, she says. As a scientist, she already knew that there are natural variations among human beings, even when it comes to sleep. In addition, she has always valued the extra time this gives her to get ahead on her workday, especially when her husband and children are still fast asleep. Even so, Bernard wondered whether she simply found it hard to relax, or whether her inability to sleep more was a sign that she was trying to take on too much."Now I have an answer," says Bernard. "I know that, genetically, this is how I am; and I'm just going to have to accept it." 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