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Scientists have pinpointed the nightly sleep range linked to healthier outcomes
Sleep is regarded by most scientific circles as the backbone of wellbeing, though maintaining a steady schedule is equally critical to overall health.
Researchers at Columbia University have found that getting too few or too many hours of sleep each night is associated with accelerated biological ageing in virtually every organ in the human body.
The study, published yesterday in Nature, drew on data from approximately half a million UK Biobank participants and employed 23 distinct biological ageing clocks to measure how different organs deteriorate over time.
The findings identified a clear sweet spot: individuals who reported sleeping between roughly 6.4 and 7.8 hours per day exhibited the healthiest ageing profiles.
Those falling outside this window - whether burning the midnight oil or spending excessive time in bed - showed signs of faster biological decline across the brain, heart, lungs, immune system and beyond.
The organ-specific clocks represent a departure from traditional ageing measures, which typically produce a single reading for the whole body.
As the study's lead author, Junhao Wen, an assistant professor of radiology at Columbia's Vagelos College of Physicians and Surgeons, explained: "Everyone is excited by these ageing clocks and their ability to predict disease and mortality risk. But to me, the more exciting question is, can we link ageing clocks to a lifestyle factor that can be modified in time to slow ageing?"
The team constructed their clocks using machine learning applied to diverse biological data - structural imaging measurements, organ-linked proteins and blood-borne molecules.
"In the liver, for example, we have an ageing clock built with protein data, an ageing clock of metabolic data, and an ageing clock of imaging data," Wen noted.
This multi-layered approach enabled the researchers to assess whether sleep patterns showed consistent associations across different molecular and biological dimensions.
The results painted a striking U-shaped curve across the body's organ systems.
Participants who reported fewer than six hours of sleep per night, alongside those clocking more than eight hours, tended to display markers of accelerated biological ageing.
The optimal range, between 6.4 and 7.8 hours, was where the lowest levels of organ deterioration were consistently observed.
Crucially, however, the researchers were careful to stress that these findings demonstrate correlation rather than causation.
Sleeping outside the ideal window does not necessarily drive organs to age more rapidly. Rather, atypical sleep duration may serve as an indicator of underlying health problems already present throughout the body. The relationship, in other words, could run in either direction.
The study also uncovered a wide spectrum of disease associations tied to sleep duration. Insufficient sleep was significantly linked to depressive episodes, anxiety disorders, obesity, type 2 diabetes, high blood pressure, ischaemic heart disease and cardiac arrhythmias.
Both extremes of the sleep spectrum — too short and too long — were connected to chronic obstructive pulmonary disease, asthma and a number of gastrointestinal conditions, among them gastritis and gastro-oesophageal reflux disease.
Wen pointed out the breadth of these connections: "The broad brain-body pattern is important because it tells us that sleep duration is a deeply embedded part of our entire physiology, with far-reaching implications across the body."
The sheer range of affected systems underscores how profoundly sleep is woven into the body's overall functioning, extending well beyond the brain alone.
The researchers delved deeper into one condition in particular, late-life depression, to explore how the organ-specific clocks might illuminate distinct biological mechanisms.
Their analysis suggested that insufficient sleep may be more directly tied to the burden of depression in later years, while excessive sleep appeared to exert its influence through pathways reflected in ageing clocks for the brain and fatty tissue.
Wen noted: "Our study suggests there may be different biological pathways between long and short sleepers that lead to the same outcome, late-life depression, and we shouldn't treat them the same way."
