Seven Hours Sleep Optimal for Longevity According to Million-Person Studies
Despite popular belief, we may not be sleeping significantly less than previous generations. Adult sleep duration has remained relatively stable since 1960, with only 15 minutes decline in youth sleep since 1970. However, optimal sleep duration matters enormously for health outcomes. Studies following over one million people reveal seven hours of nightly sleep provides the lowest risk for diabetes, cognitive impairment, and all-cause mortality. Both insufficient sleep (under seven hours) and excessive sleep (over nine hours) increase disease risk and shorten lifespan. Sleep serves critical functions including brain waste clearance through the newly discovered glymphatic system. Even one sleepless night increases Alzheimer's-associated beta-amyloid accumulation. Interestingly, pre-industrial societies naturally sleep 6.5-7 hours nightly despite no artificial lighting, suggesting this duration may be optimal for humans.