Donald Trump makes do with four hours. Tim Cook, Apple’s CEO, is up before 4am. Nearly half of all senior managers say their performance is unaffected by burning the candle. The rest of us seem positively indulgent by comparison: we get an average of seven hours and 12 minutes of shut-eye each night according to 1m worldwide users of Sleep Cycle, an app that tracks night-time sound and movement.
Even that is barely adequate. The National Sleep Foundation, an American institute, says adults need seven to nine hours a night. Sleep less and you may harm yourself and others. A 20-hour stint of wakefulness has the same debilitating effect on reasoning and reaction times as drinking a bottle of wine. Two weeks of six-hour nights slows your brain as much as pulling two consecutive all-nighters; doing so consistently increases your chance of an early death by 13%. Unfortunately you may not notice: moderately sleep-deprived people often overestimate their meagre rest-time.
Some groups sleep more than others. Sleep Cycle’s male users kip for 20 minutes less than its female ones, and toss and turn more often. Older people spend less time in rapid-eye movement (REM), which is deeper and dreamier.
Residents of most rich countries tend to be well-rested, suggesting that a good doze is something of a luxury. That link frays in Asia and the Middle East. In tiger economies like Taiwan and South Korea workers turn in at 1am on an average night. Many of those in Islamic ones have early morning prayers. Such fatigue can enfeeble an economy. Japan is the weariest nation of all: a 2016 study found that exhaustion cost it nearly 3% of its annual GDP, largely by lowering productivity.
Our disregard for sleep is relatively new. Before electric light became common, most people went to bed soon after the sun went down. No longer. Americans get an hour and a half less sleep than they did a century ago; children the world over have lost more than an hour’s slumber. The best remedy is a simple one: turn out the light.