Credit: ZME Science.
Sleep is not just rest for the brain. It is maintenance for the whole body.
A new and interesting study of about half a million adults found that people who slept around six to eight hours a night showed the lowest signs of biological ageing. People who slept less than six hours, or more than eight, tended to show faster aging in several organs and body systems.
That’s not the same as saying sleeping seven hours will slow aging. Nor does it mean everyone needs the same amount of sleep. But it offers one of the broadest looks yet at how sleep duration tracks with aging across the body — from the brain to the liver, lungs, immune system, pancreas and skin.
“Sleep affects every organ of the body,” Abigail Dove, a neuroepidemiologist at the Karolinska Institute who was not involved in the study, told Nature. “And sleep is somewhat modifiable. This is a tool that could help.”
A Sleep Pattern Written Across the Body
The study was led by Junhao Wen, a computational neuroscientist at Columbia University. Wen, who says he’s a light sleeper who often wakes up in the middle of the night, wanted to know whether poor sleep leaves marks only in the brain or across the body.
His team used data from the UK Biobank, a long-running health study of more than 500,000 people. They focused on adults aged 37 to 84 and compared self-reported sleep duration with 23 biological aging clocks.
These clocks estimate how old parts of the body appear based on MRI scans, blood proteins and metabolites — small molecules involved in metabolism. If a person’s brain, liver or immune system looks older than expected from their chronological age, the clock registers faster biological aging.
The researchers called their framework the Sleep Chart. Across many of the clocks, the same pattern appeared: a U-shape.At the bottom of the U were people sleeping roughly 6.4 to 7.8 hours a night. The exact figure depended on the organ system and the participant’s sex. On either side of the U were short sleepers and long sleepers. Nine of the 23 aging clocks showed significant links with sleep duration, including clocks tied to the brain, lungs, liver, immune system, skin, endocrine system, adipose tissue and pancreas.
×
Thank you! One more thing…
Please check your inbox and confirm your subscription.
The best point was not identical for every system. A protein-based brain clock pointed closer to eight hours. An MRI-based brain clock pointed closer to six and a half. Men and women also differed in some measures.
That makes the findings more complicated than a simple sleep rule of thumb that’s more or less helpful for everyone. There may not be one perfect number science can offer for how much sleep you should get, but the general trend stands: sleeping too much or too little can slightly accelerate the aging process. The sweet spot is somewhere between six and a half and eight hours for most people.
Why Short Sleep Fits the Biology
The link between short sleep and poor health is well established. Sleep loss has been tied to inflammation, high blood pressure, changes in blood sugar, weight gain, depression and memory problems.
The new study adds an aging layer on top. Suboptimal sleep was not only associated with faster biological ageing across several systems and with higher future risk of many diseases and conditions, including depression, anxiety, type 2 diabetes, obesity, hypertension, and ischemic heart disease.
Compared with people who slept six to eight hours, short sleepers had a 50% higher risk of death from any cause. Long sleepers had a 40% higher risk.
Those numbers do not mean sleep duration alone caused the difference. People who sleep too little may also face stress, shift work, pain, illness or social pressures that damage health. But the result fits what scientists already know: sleep helps regulate systems that keep the body stable.
The genetic results were also telling, in the sense that they didn’t matter that much. The researchers found relatively few genetic links to abnormal sleep duration.
“Sleep might be more environmental,” Wen told Nature. “It’s a strong message for the public that this can be modifiable.”
That does not mean sleep is easy to fix. Modern life often gets in the way. But it does suggest that sleep belongs alongside diet, exercise and blood pressure as a major part of health and wellbeing.
The Harder Question: Long Sleep
Most people don’t get enough sleep, but some snooze in bed more than it’s healthy. However, long sleep is more difficult to interpret.
People who slept more than eight hours also showed signs of faster biological ageing and higher disease risk. But long sleep may not always be the problem itself. It can also be a sign that something else is wrong.
Depression, sleep apnea, chronic inflammation, frailty, pain and medication can all make people sleep longer or spend more time in bed. In that case, long sleep may be less a cause than a warning light that you need to fix something about your overall health.
“Personally, I think it’s bidirectional,” Wen said.
As a caveat, the study’s sleep duration came from questionnaires rather than sleep trackers or lab tests. People often misjudge how long they sleep and the UK Biobank also does not perfectly represent the wider population.
Most importantly, the study cannot prove cause and effect. Poor sleep may speed aging, but aging, stress, and disease may worsen sleep. Both may happen at once.
Still, the work strengthens the idea that sleep is a whole-body process.
“It’s like what my grandmother would tell me: ‘You have to take care of your general health’,” Alexandra Badea, a biomedical engineer at Duke University who studies dementia, told Nature. “These systems talk to each other.”
The findings appeared in the journal Nature.