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.
Sleeping apart is increasingly common and can genuinely cut disturbance. But the lab evidence is double-edged: sharing a bed measures as slightly worse sleep yet feels better, and may even boost REM.
Probably not ideal. Even moderate light during sleep measurably raises night-time heart rate and next-morning insulin resistance, and in one large study women who slept with a light or TV on gained more weight.
A warm bedroom measurably degrades sleep, and the best-studied comfortable band sits at roughly 20–25°C. The effect is real but personal, and heat matters more than most people assume.
Yes, within limits. Short sleep is linked to more colds and weaker vaccine responses, but the strongest effects turn up when sleep is measured objectively, not from what people report.
For most healthy adults the measured difference is small. But side-sleeping has real evidence in three specific situations: nocturnal reflux, obstructive sleep apnoea and late pregnancy.
That heavy, foggy feeling on waking is often sleep inertia — a normal, temporary state, not a sign you slept badly. It bites hardest when you wake from deep sleep or during the biological night.
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.
Across the trials, the best-supported remedy is melatonin taken near destination bedtime after crossing several time zones. Light exposure is the other real lever; sleeping pills chase the symptom, not the clock.
Waking up drenched is common and, the best review found, usually nonspecific — not a sign of shortened life. In women the leading identifiable driver is the menopause, which can last far longer than most expect.
The old advice to buy the hardest mattress you can find is not what the trials show. A double-blind randomised trial and a systematic review both favour medium firmness.
Nigerian adults scored well below US and Norwegian comparison samples on a six-dimension sleep health measure. In South Africa, students with backup power were far less likely to report worse sleep during outages.
Twenty months of under-mattress sensor data from 95,819 people found that chronic irregularity was common, persistent, and tracked with 46% higher odds of hypertension.
A 327-person survey of economically distressed Eastern Kentucky counties found insomnia prevalence ranged from 44% to 83% depending on income alone.
Age, sex, employment and socioeconomic level together explained under 1% of variance in insomnia severity. Perceived stress and generalised anxiety explained close to a third.
Across 20,121 adults and 25 years of registry data, morningness markers predicted lower educational attainment but also lower odds of the bottom income quintile. Effects were absent in women.
Applying prevalence figures to UN population data yields 852 million adults with insomnia. Only 31 of 237 countries had a usable national estimate of their own.