Most adults do not need a hard eight hours of sleep; a growing body of evidence and evolutionary research suggest the optimal nightly sleep for many healthy adults is closer to seven hours, with health risks rising on either side of that range in a U‑shaped pattern.
Harvard evolutionary biologist Daniel E. Lieberman calls the rigid “8 hours” rule Industrial Era “nonsense,” noting that people without modern electricity typically sleep six to seven hours without napping, and large cohorts show the lowest mortality risk around seven hours, not eight. Lieberman expanded on the research for his book, Exercised: The Science of Physical Activity, Rest and Health, in a 2023 interview with The Diary of a CEO.
