Professor Daniel E. Lieberman, an evolutionary biologist at Harvard University, believes that the rule of sleeping 8 hours a night is a “nonsense” concept.
Theo Pedestrians On October 29, in a recent interview, Professor Lieberman affirmed that the idea that people need 8 hours of sleep has no scientific basis. Field studies in communities that do not use electric light show that their night sleep time is only about 6-7 hours. This view is increasingly reinforced by much scientific evidence and evolutionary research.
Contemporary large-scale data sets indicate a U-shaped association between sleep duration and health risks. Specifically, the risk of death from all causes and cardiovascular disease is lowest when sleeping for about 7 hours. This risk increased in both those who slept less than 7 hours and those who slept more than 9 hours. Analyzes from the UK Biobank also showed similar results.
Many reputable medical organizations also agree with this statement. The American Academy of Sleep Medicine (AASM) and the Sleep Research Society (SRS) jointly recommend that adults get “seven or more hours of sleep per night,” considering this a flexible amount of time rather than a “mandatory” eight hours. Similarly, the Mayo Clinic, one of the world’s leading medical centers, believes that adults need 7 hours or more of sleep but emphasizes the differences depending on each individual’s age, sleep quality and aging process.
Illustration photo: Inspira Health
Professor Lieberman publishes these detailed studies in the book Exercised: The Science of Physical Activity, Rest and Health (Exercise: The Science of Physical Activity, Rest and Health). He and other experts advise people to aim for 7 to 9 hours of sleep, rather than obsessing over a fixed number. The 7-hour mark can be considered the minimum time if you wake up feeling refreshed and productive.
Experts also warn that regularly sleeping less than 7 hours or having the habit of sleeping more than 9 hours are both related to health risks. If a person consistently needs more than 9 hours of sleep, they should see a doctor to check for underlying conditions such as depression, sleep apnea, or other chronic diseases. In short, the 8-hour rule is just a cultural simplification, not a universal biological requirement for everyone.