Why Some People Don’t Need as Much Sleep to Feel Refreshed

Brad Johnson’s definition of a good night’s sleep differs from most. Five hours leaves him sharp and energized. Even after a 24-hour travel day to Europe, the 70-year-old from Providence, Utah, may sleep six hours for a few nights—but never the seven or more hours recommended for adults.

“I just can't get more than four or five hours of sleep,” says Johnson, who has participated in family sleep studies. “And I thrive on that.”

For most people, this pattern would signal chronic sleep deprivation. But Johnson appears to belong to a much rarer group. Researchers call them natural short sleepers—individuals whose biological need for sleep is much lower. Only about 50 families have been identified with genetic mutations linked to the trait.

Johnson and several relatives carry a rare mutation in ADRB1. This gene impacts sleep and wake regulation, says Ying-Hui Fu, a neurology professor at the University of California, San Francisco. For decades, Fu’s team has studied families that sleep far less than others without the apparent negative effects.

Natural short sleepers do not rely on alarms or caffeine, says Fu, and the pattern often runs in families. A 2019 study in Neuron defines natural short sleepers as individuals with the lifelong tendency to naturally wake up after four to six hours of sleep, feeling restored. Even on vacations, Fu says, their sleep routine stays the same.

That consistency makes them valuable to researchers, who hope these biological outliers can reveal how the brain measures its need for sleep—and what, exactly, sleep restores.

(Inside the science of great sleep.)

In our on-the-go society, the allure is clear: needing less sleep can mean more productivity. But the body is not idle while we sleep. Crucial neurological and physiological processes continue throughout the night, says Fu. Sleep supports alertness, metabolism, glymphatic clearance, immune restoration, and mood.

Despite sleep’s importance, experts say many people routinely get less sleep than they need. According to a 2024 national health survey, nearly one in three U.S. adults report getting less than seven hours of sleep a day. That can make natural short sleepers difficult to identify. In the lab, Fu and other researchers often meet individuals who say they can get by on less sleep with alarms and caffeine.

“We call them habitual short sleepers,” says Fu. Over time, cutting sleep short is associated with an increased risk of obesity, diabetes, and coronary heart disease, according to a large meta-analysis of population studies.

The tricky part is that people may not recognize their own sleep deficit. “Humans are really bad at knowing how much sleep they need,” says Elizabeth B. Klerman, professor of neurology at Harvard Medical School and sleep investigator at Massachusetts General Hospital. In a 2005 study Klerman co-authored, young adults slept longer when researchers extended their time in bed, suggesting that their usual schedules left them with sleep debt.

“The worry in the field is that people don't recognize they're getting too little sleep because they ‘don't feel tired,’” says Klerman. “But they’ve either forgotten what alert feels like, or they're masking tiredness with caffeine. Or they just don't want to say that they're tired.”

That disconnect between feeling alert and getting enough sleep is part of the mystery researchers hope natural short sleepers can help solve.

One place researchers have looked for answers is genetics. In a 2005 Nature study, Chiara Cirelli and her team identified Minisleep, a fruit-fly with a mutation in the Shaker potassium-channel gene. It slept about one-third as much as typical flies but lived a shorter life. It was early evidence that genes can help determine how much sleep we need, says Cirelli, professor and chairperson of sleep research at the University of Wisconsin, Madison. The flies’ shorter lives also underscored that sleeping less is not necessarily the same as needing less sleep.

Four years later, Fu and longtime collaborator Louis Ptáček helped establish a genetic basis for natural short sleep in humans by discovering a mutation in DEC2. Researchers have linked familial natural short sleep to rare mutations in at least five genes—DEC2, ADRB1, NPSR1, GRM1 and SIK3.

(When you go to bed may matter more than how long you sleep.)

Together, these discoveries point to different parts of the brain’s sleep-and-wake machinery, including pathways involved in how sleep pressure builds and dissipates. But they have not yet revealed whether natural short sleepers perform restorative processes faster, need less of that restoration, or differ in some other way.

Answering that question requires scientists to understand what sleep restores in the first place. Every animal species carefully studied so far appears to sleep, says Cirelli. In humans, one hypothesis that Cirelli and other researchers have tested for decades is that sleep disconnects the brain from the environment, allowing synapses to reset through a process called synaptic homeostasis.

Some evidence suggests that natural short sleepers preserve deep, slow-wave sleep despite sleeping less, raising the possibility that their brains may complete more synaptic work in less time, says Cirelli. Fu likewise believes that natural short sleepers may accomplish some of the body’s essential overnight work more efficiently. What remains unknown is exactly which processes happen faster—or whether something else reduces their need for sleep.

“It’s really amazing to think that we spend a third of our lives sleeping, and yet the essence of sleepiness—the real thing that’s going on in the brain that causes one to fall asleep—is actually still a pretty good mystery,” says Thomas E. Scammell, professor of neurology at Harvard University and sleep neurologist at Beth Israel Deaconess Medical Center.

Scientists know that two biological systems govern sleep, says Scammell. The circadian clock helps determine timing, while homeostatic sleep pressure builds the longer a person stays awake. Much like hunger after missing a meal, that pressure makes sleep increasingly difficult to resist.

During the day, the circadian waking drive—the body’s internal morning alarm clock—helps with alertness. This push and pull explains why someone who stays up all night may feel exhausted at 3 a.m., but somewhat more alert later in the morning when the circadian waking drive begins to counter mounting sleep pressure, says Scammell.

But feeling alert does not necessarily mean the brain has finished recovering. A 1995 study found that the brain may wake when sleep pressure has fallen, and the circadian wake signal has risen. But not because every restorative process has reached one finish line.

So, how can someone tell how much sleep they actually need? Scammell suggests an experiment: for at least three nights, skip the alarm and sleep as long as the body allows. Then notice how much the sleep duration changes on the third night. If you usually sleep six hours, but naturally sleep eight hours on that third night, eight might be closer to what your body needs.

(Why eight hours of sleep may not be enough anymore.)

The number will not be the same for everyone. “Saying everybody needs to sleep eight hours is like saying everybody needs to be five-foot-three [in height],” says Fu. Genes and environment help shape how much sleep each person needs, she says, making sleep an individual trait much like height or personality.

Natural short sleepers sit at one extreme of that variation. Fu’s larger goal is to understand how these rare natural short sleepers accomplish the body’s essential overnight work in less time—and whether that knowledge could eventually improve sleep for everyone.

For Johnson, that distinction was personal. For years, articles recommending seven or eight hours of sleep made him fear that his short nights were quietly harming him. “I lived with this fear until the sleep center people said, ‘That’s normal for a short sleeper,’” he says. “That made a difference for me.”