The old advice was simple: get eight hours. A sweeping new study suggests the picture is more nuanced — and more individual.
A Nature paper published in May 2026 analysed roughly half a million UK Biobank participants and found a U-shaped link between self-reported sleep duration and biological ageing across the body. Too little sleep is bad. So, it turns out, may be too much. The lowest biological age gaps clustered around 6.4 to 7.8 hours per night.
A recent NZ Herald summary of the Washington Post coverage is a useful plain-language walkthrough of the findings and what they do — and do not — mean for daily life.
What the researchers measured
Lead author Junhao Wen, a radiology researcher at Columbia University, has been building biological ageing clocks: models that use imaging, blood proteins and metabolites to estimate how fast different organs are ageing compared with chronological age.
The hypothesis is that organs within the same person can age at different rates. Wen’s team asked whether sleep duration was linked to those organ-specific clocks.
Using UK Biobank data, they developed clocks for organs throughout the body and compared them with how long participants said they slept. For nearly every organ measured, both short and long sleep were associated with faster biological ageing. Small deviations from the sweet spot showed smaller effects; larger deviations showed more.
Columbia’s press summary puts the practical framing well: this does not prove that sleep alone causes organs to age faster or slower, but it suggests that both insufficient and excessive sleep may be markers of poorer health across a coordinated brain-body network.
The Goldilocks zone
Mark Lachs, a geriatrics specialist at Weill Cornell who was not involved in the study, described it as a Goldilocks phenomenon: too little is bad, too much is bad.
Wen himself treats the finding as guidance, not a prescription. The key message is consistent sleep, roughly six to eight hours, tuned to what your body actually needs.
That matters because most people are not oversleeping. Sleep medicine clinicians repeatedly note that short sleep is the common problem, and true “short sleepers” who thrive on very little sleep are relatively rare.
Women may need slightly more
One subtle pattern: women seemed to do best with a little more sleep than men in some organ clocks. In one brain clock, men aged least around 7.7 hours; women’s brains showed the smallest age gap at about 7.82 hours — roughly 15–20 minutes more.
That lines up with population data showing women tend to report slightly longer sleep than men. Hormones, physiology and social factors may all play a role.
Why might long sleep look harmful?
More than eight hours was associated with faster ageing in this dataset. That surprises people who treat “more sleep” as always virtuous.
Researchers offer two important caveats:
- Reverse causation. Poor health can make people sleep longer. Observational studies link sleep duration and ageing; they cannot fully separate cause from effect.
- Context matters. In some conditions, such as depression, sleeping more can worsen symptoms rather than fix them.
So long sleep may sometimes be a symptom of underlying illness, not the driver of accelerated ageing.
Limitations to keep in mind
The UK Biobank skews toward people of White European ancestry. Wen has called for more research in Asian and African populations.
Sleep was self-reported, not measured with wearables. Individual needs vary with genetics, work schedules, training load, illness and life stage. The 6.4–7.8 hour window is a population average, not a target for everyone.
Practical habits that still hold
The study adds precision to something sleep researchers have said for years: quality, consistent sleep is one of the highest-return health habits you can build.
Useful starting points:
- Keep a steady wake time, including weekends, to anchor your circadian rhythm.
- Get morning light within the first 15–20 minutes after waking — it helps set the body clock.
- Wind down screen use in the hour before bed; late-night phone scrolling is one of the easiest disruptions to remove.
- Make the bedroom dark, quiet and cool — roughly 18°C / 65°F is a common target.
- Stop caffeine by mid-afternoon if you are a slow metaboliser.
- If anxiety keeps you awake, try scheduling “worry time” earlier in the day or cognitive shuffling techniques rather than lying in bed ruminating.
If you feel tired during the day, you may need an earlier bedtime — or fewer late-night habits working against you — not a rigid chase of a single number on the clock.
The longevity takeaway
Sleep is not passive downtime. It is when the body repairs tissue, regulates metabolism, consolidates memory and resets immune and hormonal systems.
This study underscores that sleep duration sits on a curve, not a straight “more is better” line. For most adults, the useful band is roughly six to eight hours, with consistency mattering as much as the headline figure.
As geriatrician Mark Lachs put it: there is little a clinician can offer that beats a good night’s sleep. The new data suggests the “just right” amount may be a little less than the cultural eight-hour default — but the right answer for you is still the amount that leaves you rested, alert and able to exercise, eat well and stay connected.
Treat sleep as a non-negotiable part of your longevity stack. Then tune it to your body, not to a meme.