On May 13, 2026, researchers from the MULTI Consortium published in Nature a study dedicated to sleep and biological aging. Their goal was to determine the duration of sleep associated with the slowest aging of the organism. To do this, the scientists analyzed data from nearly 500,000 participants drawn from the UK Biobank.
An ideal window between 6 and 8 hours
Contrary to general recommendations often cited for years, this study shows that optimal sleep does not necessarily correspond to eight exact hours. The researchers identified a much more precise range. According to their analyses, the slowest biological aging appears when sleep is between 6.4 hours and 7.8 hours per night. To reach this conclusion, the scientists used 23 “biological clocks.” Some relied on blood proteins. Others analyzed metabolites produced by the body. Finally, several assessments were conducted using MRIs of the brain, liver, heart, or pancreas. This methodology allowed the measurement of the organs’ actual aging, and not merely the subjective feeling of fatigue upon waking.
For example, the brain shows an ideal sleep duration close to 6.5 hours when viewed with MRI, while some biological analyses reach up to 7.8 hours in women. The results thus sketch a very clear U-shaped curve. Below six hours, biological aging accelerates. Above eight hours, the phenomenon also reappears. This sleep-health relationship is not entirely new, either. As early as 2022, researchers from the universities of Cambridge and Fudan had observed that roughly seven hours of sleep were associated with better cognitive performance and better mental health after age 40.
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Why too much sleep can also harm health
For a long time, sleep deprivation has captured all the attention of specialists. Yet this new study reminds us that too much sleep can also become a concerning signal for health. The researchers caution, however, that sleeping more than eight hours would not necessarily be the direct cause of accelerated aging. According to them, this prolonged sleep could rather reflect preexisting biological imbalances in the body. The scientists notably observed genetic correlations between excessive sleep and several neuropsychiatric disorders. People regularly sleeping more than eight hours showed more links with depression, bipolar disorder, schizophrenia, or ADHD. Again, the study does not demonstrate a direct causal link. However, it points to a recurring phenomenon: too-long sleep often appears as a marker of biological fragility.
Meanwhile, the consequences of insufficient sleep remain substantial for health. According to the Foundation for Medical Research, nights of less than six hours raise the risk of type 2 diabetes by 28%, while very short sleep also increases cardiovascular risk. Researchers at Inserm also note a 20% increased risk of developing a first chronic disease by age 50 when sleep does not exceed five hours per night. This issue becomes even more significant as the sleep patterns of the French continue to decline. Public Health France already indicated that about 25% of young adults slept less than six hours per night on weekdays, in a report focused on sleep published in 2019. The average sleep time remains close to seven hours, but short nights have risen sharply in recent years.
Sleep, aging and biological balance: what this study reveals
The major strength of this study lies in its ability to observe biological aging directly. The researchers did not merely question participants about fatigue or sleep quality. They compared sleep durations to the actual state of organs and physiological systems. This approach gives the results unprecedented scientific weight. The authors notably found that each organ has a different sensitivity to sleep. The endocrine system, responsible for producing hormones, appears to function best with about 6.1 hours of sleep in men and 6.7 hours in women, according to the data relayed by Presse-citron. The brain, by contrast, requires slightly more rest according to the evaluation methods used.
This precision could alter public health recommendations around sleep. Up to now, guidance rested largely on average estimates. Now, researchers have biomarkers capable of concretely measuring sleep’s impact on the body. The study, however, has several limitations. Sleep data were largely based on participants’ self-reports. The researchers therefore acknowledge that a more objective measure, via specialized devices such as polysomnography or actigraphy, would have strengthened the precision of the results. Additionally, most participants were of European origin, which limits the global generalizability of the conclusions.
Despite these caveats, this research stands today as one of the most important analyses ever conducted on sleep and biological aging. Its central takeaway remains clear: the human body seems to function best within a relatively narrow balance zone. Sleeping less than six hours gradually weakens the body. Sleeping more than eight hours could also signal health deterioration. Between the two, around seven hours of sleep, researchers observe the most favorable biological markers.
