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Most people already know they feel better after a good night’s rest. But how many hours count as a good night’s rest? Eight? Nine?
What constitutes healthy sleep varies from person to person. In fact, it turns out that the amount of sleep we need varies more than health experts once thought. This is based on a new understanding of what’s known as familial natural short sleep, or FNSS, as detailed in a study in March 2022 in iScience.
FNSS results from ADRB1 and NPSR1 genetic mutations that allow a person to function on much less sleep than the average person. These sleepers reap the health benefits of a full night’s sleep, sometimes in half the number of hours.
This trait could help scientists understand how to fight health conditions linked to poor sleep, such as Alzheimer’s disease.
To appreciate how short sleep works, it’s important to understand the key role sleep plays in good health. Harvard Medical School explains that sleep is when your body goes about the process of repairing itself. It undertakes such crucial functions as making proteins, releasing growth hormones, growing muscles, and repairing tissue. Think of it as a time when your body is fixing all the wear and tear that happens to you when you’re awake.
Sleep is also a time when your body clears away a byproduct called adenosine, which builds up in your brain and causes the feeling of tiredness. If you’re sleep-deprived, your body can’t keep up with all these restorative functions, so physical and mental health suffer.
But sleepers with FNSS may be able to do all of this in four hours to six hours compared with the typical eight or nine hours most people need.
“We don’t really know how these genes modify people’s sleep yet,” says Dr. Ying-Hui Fu, co-author of the study with Dr. Louis Ptáček. “The people with familial natural short sleep mutations seem to be able to sleep less without obvious negative long-term problems. This suggests that sleep in FNSS might be more efficient in the restoration process.”
Drs. Fu and Ptáček hail from the University of California, San Francisco, and have studied FNSS for more than a decade. It’s important to note, they say, that they do not perform genetic testing to find out whether an individual can get by with short sleep.
“We determine that people have FNSS not with genetics but by getting a detailed history from people about their sleep habits and how they feel after sleeping a certain amount,” Dr. Fu says. “At a basic level, our operational definition of FNSS is a lifelong pattern of sleeping four to six hours a night, feeling well-rested, and not desiring any additional sleep.”
FNSS isn’t common. Drs. Fu and Ptáček estimate that roughly one in every 2,500 to 5,000 people have this genetic mutation. And what might be most significant about these sleepers is that they are seemingly resistant to the declining brain health that affects people who get too little sleep. Their brains stay as strong and healthy in old age as they were in their youth. These sleepers may not develop conditions such as Alzheimer’s disease. This may be because good, effective sleep means there’s less build-up of waste products within the brain or there’s more efficient removal of brain waste, Dr. Fu says, though it’s not yet clear which.
In this most recent study, the researchers studied mice with the short-sleep genetic makeup and saw how the faster rate of repair during sleep meant the subjects were resistant to nerve cell damage or cell death. They also saw fewer deposits of tau protein and amyloid plaques, which are hallmarks of Alzheimer’s disease.
The authors say that by understanding how this short-sleeper genetic mutation affects sleep quality, we could find ways to improve sleep for other people. They favor this strategy of using knowledge to aid prevention rather than trying to develop treatments for conditions like Alzheimer’s disease after symptoms have already started to appear.
Though Drs. Fu and Ptáček are champions of healthy sleep, they are not Alzheimer’s disease researchers.
“This study is a way to demonstrate to people why sleep is important,” Dr. Ptáček says. “[Alzheimer’s disease] is only one of many diseases that can be affected by poor sleep quality.”
As for people who think they might be elite sleepers with the FNSS genetic mutation: It’s always possible. But don’t go making drastic changes to your lifestyle just yet.
“The message that we want to spread is that we’re all unique,” Dr. Fu says. “We have many differences, including sleep timing and need. Our sleep ‘needs’ are dictated by our genetics.”
Although some people can get by on four hours of sleep — or think they can — others need 10 hours of sleep.
“The important thing for each of us is that we get the sleep we need,” Dr. Fu says.
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