Researchers say sleep regularity and quality may matter more than duration

Researchers said the widely held belief that adults need eight hours of sleep is not an absolute standard, with sleep quality, regularity and timing potentially more influential than a fixed hourly target. A review drawing on data from anthropology, genetics and history found that the main difference between modern and pre-industrial societies lies less in total sleep duration than in sleep patterns and their alignment with natural light. The researchers noted that in traditional societies people tended to fall asleep around sunset and wake at dawn, tying sleep cycles more closely to the natural light-dark rhythm. They said the spread of artificial lighting, screen use, noise and irregular schedules has pushed bedtimes later and reduced sleep quality. The team also addressed the long-running claim that pre-industrial humans slept in two distinct phases, a "first sleep" and a "second sleep." Researchers said historical sources supporting that view can be interpreted in different ways and that modern experiments conducted in full darkness do not fully replicate past living conditions, leaving the debate unresolved.