Can You Sleep Too Much? New Research Suggests There’s a Sweet Spot

Researchers found a U-shaped relationship between sleep and biological aging, suggesting that more sleep isn’t always better.

More sleep is better. At least, that’s what we’ve been told, and it’s led to a deluge of content about catching up on lost sleep, sleep hygiene, even how to pick the right pillow to optimize your Zzzs. Sleep more, and you’ll think more clearly, have a stronger immune system, and even increase your athletic performance. And while sleep is indeed crucial, new research has unearthed a bit of nuance: Sleeping significantly more isn’t necessarily associated with better health, either.

What You Should Know About the Sleep “Sweet Spot”

In a study published in Nature, researchers found a U-shaped relationship between sleep duration and markers of biological aging. Across several of the biological “aging clocks” they analyzed, the lowest biological-age gaps occurred between about 6.4 and 7.8 hours of sleep, depending on the organ and the person’s sex. Sleeping less than six or more than eight hours, meanwhile, was associated with greater risks of numerous diseases and all-cause mortality. 

That complicates the familiar “everyone needs eight hours” guidance, and it lines up with CDC-cited research tying under-seven-hour sleep to higher rates of high blood pressure and heart disease. Mark Lachs, a geriatrician at Weill Cornell Medicine who wasn’t involved in the study, framed it to the Washington Post as a Goldilocks problem: too little sleep is bad, and so is too much.

That range sits a bit under the stock suggestion of “eight hours per night,” but it doesn’t necessarily mean you should start setting your alarm for six and a half hours. The researchers weren’t trying to establish a new sleep prescription, and the ideal duration varied across the biological systems they measured. There’s also normal human variation to account for. Individual needs vary widely: some people do fine on six hours, others need closer to nine, and a rare few — under 1% of people — function on roughly four, a quirk researchers have tied to rare genetic variants that affect sleep regulation. The takeaway isn’t that 7.1 hours is some magical number, but more that in this enormous dataset, both very short and very long sleep were associated with worse biological aging and health outcomes.

Going Deeper: What the Study Did

To conduct the study, researchers analyzed data from the UK Biobank — a well-known, widely used database containing detailed health information from about 500,000 volunteer participants. They compared self-reported sleep duration against 23 different biological “aging clocks” built from organ MRIs, blood proteins, and metabolites. The idea is that your organs don’t necessarily age at the same rate, so these clocks allowed researchers to look at signs of aging across different parts of the body rather than simply assigning each person one biological age.

What emerged was a U-shaped curve. Across the nine aging clocks that showed a significant relationship with sleep, the lowest markers of biological aging generally fell somewhere between 6.4 and 7.8 hours. Move farther in either direction, and those markers tended to rise. Again, that doesn’t make 6.4 to 7.8 hours a magic range: Different organs had different low points, and the researchers used a broader six-to-eight-hour range as “normal” when looking at health outcomes. Compared with that group, people sleeping under six or over eight hours had a higher risk of all-cause mortality and various diseases.

There are some important caveats. The UK Biobank population is predominantly White and of European ancestry, which limits how confidently these findings can be generalized to the broader population. Sleep duration was also self-reported, which is less precise than objectively measuring how long someone actually sleeps. And especially on the long-sleep side of the curve, it’s difficult to know which came first. Poor health or conditions such as depression could lead someone to sleep longer, rather than longer sleep being the thing that causes poorer health. The researchers tried to tease out that relationship genetically, but couldn’t completely rule out reverse causation.

The Takeaway

These findings, the researchers insist, should be considered guidance, not concrete. Getting a consistent six to eight hours of sleep may be a reasonable target for many adults, but there’s no need to obsess over hitting an exact number every night. Sleep regularity and how you actually feel matter, too.

Bottom Line

This was a massive study, and the U-shaped relationship between sleep duration and biological aging is worth attention. But it was still observational, relied heavily on self-reported sleep, and drew from a population that was largely White and European. Longer sleep may also be a sign of poor health rather than the cause of it, so don’t start cutting sleep just to land inside a supposed sweet spot.