For how we live.
In 425 US adolescents followed with phone sensors and Fitbits across 7,591 nights, heavier-than-usual late-evening phone use tracked with later, shorter sleep — the association growing hour by hour toward midnight.
The viral countdown says no caffeine 10 hours before bed, no food at 3, no work at 2, no screens at 1. The caffeine and food steps have real evidence behind them; the rest is thinner.
A large public randomised trial found reading a book in bed nudged sleep quality up. But the format matters: paper helps, while a glowing screen can quietly work against you.
The advice to look 20 feet away for 20 seconds every 20 minutes is everywhere. A two-week trial in symptomatic computer users found it cut eye-strain and dry-eye symptoms, but changed no measurable sign of eye health.
Compulsively scrolling bad news tracks with worse mental and physical health — but the strongest studies show association, not proof, and the scariest prevalence figure shrank by half on replication.
The WHO sets clear screen-time limits by age: none under two, an hour or less from two. The evidence behind them is real but modest — and the direction of cause and effect is not as simple as it sounds.
Across 17 randomised trials, blue-light filtering lenses showed no clear benefit for eye strain, vision or sleep. The evening-screen problem they target is real; this is not the fix.
Restrictive English schools cut phone use during the school day but not overall — and teenagers' wellbeing was no better than at schools that allow phones. What tracks with worse mental health is heavy, problematic use.
A German trial in 1,793 students found a cognitive-behavioural programme reduced gaming and internet-use disorder symptoms only in high-risk adolescents — not across the whole classroom.
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 422-family cohort with a pre-ban baseline is the closest thing to a controlled test the world has. Researchers are also warning the law will make studying adolescents harder — including studying this.
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.
Eye strain is close to universal among heavy device users, and it is temporary. The evidence that screen time causes myopia is real but weak, and every study of it measured screen time by questionnaire.
Longitudinal data and a meta-analysis of 159,425 children find consistent associations between screen time and development — but the effects are small, observational, and thinner than the guidelines imply.
A cluster-randomised trial in Guangzhou cut three-year myopia incidence by 9.1 percentage points with 40 extra minutes outdoors a day. The eye's underlying growth barely changed.
A month-long trial that blocked mobile internet improved mental health and attention, and a one-week social-media break lifted wellbeing. The wider literature is thinner.