A new analysis of biological aging across the human body reveals that both sleeping too little and sleeping too much are associated with faster aging in the brain, heart, lungs, immune system, and other organs, linking these sleep patterns to a broad range of diseases. 
While previous studies have found that sleep is largely linked to aging and the pathological burden of the brain, study leader Junhao Wen, assistant professor of radiology at Columbia University Vagelos College of Physicians and Surgeons, notes, "Our study goes further and shows that too little and too much sleep are associated with faster aging in nearly every organ, supporting the idea that sleep is important in maintaining organ health within a coordinated brain-body network, including metabolic balance and a healthy immune system." 
Utilizing "aging clocks"—machine learning tools that estimate biological age based on data like blood proteins and medical imaging—Wen and his colleagues analyzed data from approximately half a million UK Biobank participants to create organ-specific clocks rather than relying on single-body measures. 
Wen explains the motivation behind this approach: "Everyone is excited by these aging clocks and their ability to predict disease and mortality risk," but adds, "But to me, the more exciting question is, can we link aging clocks to a lifestyle factor that can be modified in time to slow aging?" 
Driven by mounting evidence of sleep's role in health and a personal interest as a light sleeper, Wen states, "I'm also a light sleeper and was getting worried about the effects on myself," the team constructed clocks using structural measurements, organ-specific proteins, and blood molecules, noting, "In the liver, for example, we have an aging clock built with protein data, an aging clock of metabolic data, and an aging clock of imaging data," which "allows us to see whether sleep is distinctively associated with aging clocks derived from multiple omics and molecular layers." 
By comparing self-reported sleep duration with biological age estimates from 23 clocks covering 17 organ systems, the researchers identified a clear U-shaped pattern where individuals sleeping fewer than 6 hours or more than 8 hours exhibited faster biological aging, while the lowest aging levels occurred in those sleeping between 6.4 and 7.8 hours. 
Although the findings do not prove causation, suggesting instead that extreme sleep durations may signal poorer overall health, the study highlights a profound connection between sleep, the brain, and the rest of the body, with short sleep linked to depressive episodes, anxiety, obesity, type 2 diabetes, hypertension, and heart issues, while both short and long sleep were associated with respiratory and digestive disorders. 
Emphasizing the significance of these results, Wen says, "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." 
Further investigation into late-life depression using mediation analysis revealed that while the causal direction remains unclear, short sleep may be more directly connected to depression burden, whereas long sleep might influence depression through pathways reflected in brain and adipose tissue aging clocks, leading Wen to conclude, "This has a strong implication for future sleep management and future therapeutics," and "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."