For how we live.
The number most people quote is not the number the American Academy of Sleep Medicine and Sleep Research Society agreed on. Their recommendation is a floor, set by expert vote rather than by trial.
A UK Biobank analysis of 96,365 people found a dose-response relationship between lifetime night-shift exposure and cardiovascular-kidney-metabolic disease — amplified in those who also slept short.
In a US cohort followed eight years, average weekday sleep rose from 8.1 to 8.3 hours while reports of fatigue and trouble sleeping increased. The socioeconomic gap in duration closed; the gap in symptoms did not.
In a US cohort wearing wrist actigraphs, self-reported sleep exceeded measured sleep by about half an hour, with the gap largest on weekends and among Black adolescents and those from lower-income households.
In 24,223 Swedish workers followed to 2018, insomnia and long sleep raised cardiovascular risk only when accompanied by daytime impairment — and rising sleep duration preceded disease.