Too little sleep can be harmful for health in the long run, but a sweeping study suggests that too much sleep also may not be ideal: It’s associated with accelerated aging in nearly every organ in the body.

Before you nap lovers totally lose it, the researchers emphasized that the amount of sleep each person needs varies based on genetics, environment, lifestyle and other factors. Some people need 6 hours, while others need 9.

However, the new research, published in the journal Nature on May 13, does suggest that there’s a sleep “sweet spot” between 6.4 and 7.8 hours of sleep a night. People who hit that amount had better functioning of the immune system, brain and heart, as well as other organs, when measured on the molecular level.

“Too little sleep is bad and too much sleep is bad,” said Mark Lachs, co-chief of the Division of Geriatrics and Palliative Medicine at Weill Cornell Medicine and NewYork-Presbyterian Hospital, who wasn’t involved in the study. “It is a Goldilocks kind of phenomenon.”

The study’s researchers used sophisticated statistical models to determine that both too much and too little sleep are associated with molecular changes consistent with accelerated aging.
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“I would treat this as guidance,” said Junhao Wen, an assistant professor of radiology at Columbia University and lead author on the study. “The key point is consistent sleep time, around 6 to 8 hours per day. We know that’s going to do good for your overall health.”

Sleep matters for the whole body
Wen became interested in studying sleep because of a goal to improve his own shut-eye.

“I’m a light sleeper,” Wen said. “I’m a little bit concerned about my personal sleep quality.”

Wen’s lab has been at the forefront of developing biological aging clocks, which use biomedical data and machine learning to determine the physiological age of each organ.
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“The hypothesis is that different organs, even within the same person, age at different rates,” Wen said.

Drawing on the UK Biobank, a longitudinal study involving 500,000 volunteers, Wen and his colleagues developed aging clocks for organs throughout the body to see if the aging of various parts of the body was linked to the amount of sleep.

For nearly every organ, too much or too little sleep was associated with accelerated aging, at least by their measurements.

The effects formed a U-shaped curve, meaning small deviations from the sleep “sweet spot” showed smaller amounts of organ aging, and larger deviations showed more substantial aging.

Previous research has suggested that there could be an optimal amount of sleep associated with improving the function of the nervous system, the circulatory system, the endocrine system and other organs throughout the body.

“Across the board, this optimal sleep duration hovers around 6.5 to 7.5 hours,” said Marie-Pierre St-Onge, a professor of nutritional medicine and Director of the Center of Excellence for Sleep & Circadian Research at Columbia University, who was not involved in the study.

Women may need more sleep than men
One pattern that emerged in the data is that women seem to need a bit more sleep than men to function best.

For example, in one of the brain clocks the researchers looked at, men seemed to do best with 7.7 hours on average, while women’s brains aged the least with 7.82 hours per night.

“Women seem to do better with a little longer,” St-Onge noted. “About 15, 20 minutes — which is interesting because it matches what we see in the general population and self-reported sleep duration, that tends to be slightly longer in women than men.”

The researchers said this could be because of hormones or other physiological factors, as well as social factors.

Because sleep needs are individual, experts recommend that if you’re feeling tired during the day, you may need to adjust your bedtime a little earlier, and change your habits throughout the day to support good sleep.

“Have some light exposure if possible within that first 15 to 20 minutes of waking up,” said Ana Krieger, a professor of medicine and Medical Director of the Center for Sleep Medicine at Weill Cornell, who wasn’t involved in the study. “That’s very important because it helps regulate the circadian rhythm.”

How could too much sleep be bad?
It may surprise people that more than 8 hours of sleep is associated with faster aging of the body.

The researchers said this could be because poor health is making people sleep longer. (And this type of study can’t prove that the sleep amount is the cause of the slower or faster aging, just that the two factors are linked.)

But in some cases, as with depression, Wen noted, sleeping more may also exacerbate the condition.

Limitations of the study
The UK Biobank data skews toward people of White European ancestry.

Wen said more research is needed involving people of Asian and African descent.

Wen emphasized that this finding isn’t meant to be prescriptive. While people on average in the study thrived with between 6.4 and 7.8 hours of sleep, many people may need more or less than that.

Sleep experts recommend tuning into what works best for your own body by minimizing disruptions such as late-night phone use and observing what your body naturally does. If anxiety is keeping you awake, experts suggest trying techniques like cognitive shuffling or scheduling “worry time” earlier in the day.

While too much sleep can be a problem, that’s not the sleep problem most people face.

“Often people underestimate their needs‚” Krieger said.

Experts said the vast majority of people need around 6 to 8 hours, and so-called “short sleepers” are relatively rare.
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Krieger and other researchers emphasized that sleeping well is probably one of the best things for our health, because it makes exercising, socializing and other healthy activities easier. She said that modifications including putting electronics away and ensuring your bedroom is dark, quiet and cool can help set you up for a good night’s sleep.

Researchers said this study underscores the importance of quality sleep for the functioning of every part of the body.

“There is nothing that I can do for a patient that’s better than a good night’s sleep,” Lachs said.