The Siesta Was Right: What the Evidence Says About a Twenty-Minute Nap and a Ninety-Minute One

Somewhere between one and four in the afternoon, most people's alertness falls. It happens whether or not you ate lunch, whether or not you slept well, and in every culture that has been measured; it is a second, smaller trough in the same circadian rhythm that puts you to sleep at night. Cultures that built a rest into that hour, from Andalusia to the Gulf, were not being lazy. They were following the clock. Cultures that abolished the rest to fit the factory day did not abolish the dip; they just started drinking coffee at three.

The twenty-minute nap

The Sleep Foundation's summary of the research is consistent with what NASA found when it tested naps on long-haul pilots: a nap of ten to twenty minutes improves alertness, reaction time and mood for the next two or three hours, and does so without the heavy-headed feeling that follows a longer sleep. The reason is sleep architecture. In the first twenty minutes you are in light sleep, stages one and two, and waking from those is easy. Beyond about thirty minutes you enter slow-wave sleep, and waking from that is the fog that gives napping its bad name. Set an alarm for 25 minutes, allowing five to drift off, and the fog does not happen.

The ninety-minute nap

A full sleep cycle takes roughly 90 minutes and includes slow-wave and REM sleep. A nap of that length, taken after a genuinely bad night, restores more than alertness; there is reasonable evidence it helps memory consolidation and emotional regulation in the way night sleep does. It also wakes you at the end of a cycle, when arousal is naturally light. The price is that it takes pressure off the following night, and a 90-minute nap at three will push your bedtime back or thin your sleep. It is a repair tool for shift workers, new parents and the jet-lagged, not a daily habit for people who sleep normally.

The forty-minute mistake

The naps that leave you worse than before are the ones in between, roughly 30 to 60 minutes, that wake you from deep sleep with none of the benefit of a completed cycle. If your naps make you feel terrible, they are almost certainly this length. Shorten them or lengthen them.

Who should not

People who struggle to fall asleep at night should be careful, because any daytime sleep reduces the sleep pressure that gets them off at eleven; the NHS advice for insomnia is no napping at all. A sudden new need to nap, or naps that no longer refresh, are worth mentioning to a doctor, since they can be a sign of sleep apnoea or of night sleep that is worse than you think. And napping after about four in the afternoon, whatever the length, cuts into the night.

How

Early afternoon, in the dip. Lying down or well reclined; sitting upright roughly doubles the time it takes to drop off. Dark and cool if you can manage it, an eye mask if you cannot. Coffee immediately before a twenty-minute nap is a genuine trick: caffeine takes about that long to act, so you wake as it arrives. And no guilt. A society that schedules a meeting at two and then wonders why nobody contributes has the physiology wrong. Our piece on daily routine and the body clock puts the afternoon in the context of the whole day.