Eight hours a night, they told you. But the largest sleep study ever conducted now suggests that might actually be a bit too much.
Writing in the journal Nature, researchers said sleeping more than eight hours was associated with faster biological aging. The sweet spot, across nearly every organ in your body, tops out slightly less, at around 7.8 hours.
500,000 adults
Led by Junhao Wen of the Vagelos College of Physicians and Surgeons, the Columbia University researchers analyzed data from roughly 500,000 adults in the UK Biobank. Participants were between 37 and 84 years old.
Using machine learning, the team built 23 biological aging clocks across 17 organ systems: brain, heart, lungs, liver, immune system, fat tissue, and more.
These clocks estimate how biologically old each organ looks, based on medical imaging, blood proteins, and metabolic markers.
Across all 17 systems, the same U-shaped pattern emerged. People sleeping fewer than six hours showed accelerated biological aging. But so did people sleeping more than eight hours. The lowest aging rates appeared in people sleeping roughly 6.4 to 7.8 hours. There were slight differences by sex: women’s optimal range ran 6.5 to 7.8 hours; men’s was 6.4 to 7.7.
Not the first time
The “too much” finding isn’t entirely new.
A few years ago in this space, I wrote about a 44,000-person study that found people who slept beyond the recommended window were “equally impaired as those who slept too little.”
Researchers at the time admitted they didn’t know why, but the Columbia study helps answer that.
Long sleep was associated with faster aging across multiple organ systems, with a particular signal running through fat tissue, which the researchers link to systemic inflammation.
Their best explanation: Sleeping too much is often a marker of underlying illness rather than a direct cause of aging. Sick people sleep more.
But when the same pattern shows up across 17 independent biological clocks in half a million people, it’s hard to wave away.
Earlier research tended to focus narrowly on the brain.
A 2025 MIT study found that during attention lapses after a sleepless night, waves of cerebrospinal fluid surge through the brain performing the same cleanup that normally happens during sleep — the brain forcing maintenance on itself whether you’re ready or not.
And a separate UK Biobank study of 88,000 people linked poor sleep to 172 different diseases.
This Columbia study goes further — asking what decades of a given sleep pattern do to your organs collectively. The answer runs from your brain to your lungs to your liver:
Short sleep was specifically linked to depression, anxiety, obesity, Type 2 diabetes, hypertension, and heart arrhythmias.
Both short and long sleep were associated with COPD, asthma, and digestive disorders including GERD.
The researchers also found that short and long sleepers may arrive at late-life depression through different biological pathways, which suggests perhaps they should be treated the same way clinically.
A light sleeper, himself
Sleep duration here was self-reported, not device-tracked, and the study was observational, so it shows association, not causation.
Importantly, the optimal range is a population average. Your own number may differ.
Wen mentioned he’s a light sleeper himself and was partly motivated by personal concern.
He wanted to know whether sleep — something people can actually control — was measurably tied to how fast the body ages. Across half a million people and 17 organ systems, the answer was yes.
The target, then, isn’t eight. It’s somewhere between 6.4 and 7.8, with the exact number varying a bit by organ and by sex.
For most people, that means aiming for roughly seven, which, as it turns out, is probably what your body has been asking for all along.
Personal note: I’m finishing this at 11 p.m., and I have to be up at 6:30 a.m. Turns out maybe I’ve been timing this all perfectly without even realizing it.
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Thanks for reading. Photo by Annie Spratt on Unsplash. I wrote about some of this at Inc.com. See you in the comments.