Sleeping Less Than Six or More Than Eight Hours Linked to Faster Biological Aging

Too little and too much sleep are both linked to faster biological aging across several body systems at once. That’s the conclusion of an international team of researchers who analyzed data from the UK Biobank. The study was published in the journal Nature.

The scientists compared sleep duration against 23 models of biological age covering 17 organs and body systems. The models were built using MRI data, blood plasma proteins and metabolites.

Sleep duration data was collected from roughly 500,000 UK Biobank participants aged 37 to 84. People reported on their own how much they slept per day on average, including daytime naps. Data availability for individual biological “clocks” varied, however, so not all 500,000 people took part in every specific analysis.

About seven hours of sleep corresponded to the lowest biological age

In nine of the 23 measures, researchers found a statistically significant U-shaped relationship: biological age rose with both too little and too much sleep.

The smallest gap between biological and chronological age appeared at roughly 6.4–7.8 hours of sleep per day. The exact point varied by sex and by specific body system.

In the study, sleep was considered short at less than six hours, normal at six to eight hours, and long at more than eight hours.

The link showed up at different levels. The U-shaped relationship appeared, in particular, in measures tied to the brain, lungs, liver, immune system, skin, endocrine system, fat tissue and pancreas.

The authors drew on several types of data at once, so the study captures not only structural changes in organs on medical images but also differences in molecular markers of aging.

Long sleep doesn’t necessarily make the body age

Extreme sleep durations were also linked to a higher risk of several diseases and overall mortality. Among the examples the authors cite are depression and diabetes. The researchers also used data from other medical and genetic databases to test how robust the patterns they found were.

However, the study does not prove that sleeping more than eight hours itself accelerates aging. The link to long sleep in particular should be interpreted with caution: needing more sleep may be a consequence of an existing illness, declining health or other factors.

There’s another limitation — sleep duration was mostly self-reported rather than tracked continuously with objective monitoring. The authors note separately that self-reported sleep correlates only moderately with measurements from wearables or polysomnography.

So the 6.4–7.8 hour range should not be taken as a universal norm for everyone. The study describes statistical patterns in a large middle-aged and older population; it does not establish an exact amount of sleep after which accelerated aging begins.

The study’s main distinguishing feature lies elsewhere: the link between sleep duration and biological age turned up not only in the brain but in several organs at once and at different biological levels. That reinforces the view of sleep as a factor tied to the state of the whole body, not just the nervous system.