For how we live.
Two large re-analyses of the same public datasets found the association is real, negative and very small. A third review found the association is not even consistent between the Global North and South.
A laboratory trial found a light-emitting e-reader really does suppress melatonin and delay the body clock. Two 2026 field studies found the day-to-day effect runs almost entirely through when people go to bed.
Among 16-to-24-year-olds in NHANES, those who slept longer on weekends had 41% lower odds of daily depressive symptoms. The survey measured both at the same moment, which limits what can be concluded.
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.