Naps: are they good for you, and how long should they be?

Do naps help?

For alertness, yes. Lab studies in healthy adults, summarised in a 2009 review, show that a short daytime nap improves alertness, reaction times and some kinds of memory. Brief naps of around 10 minutes gave benefits almost straight away. Longer naps, of 30 minutes or more, gave benefits that lasted longer but often came with a period of grogginess first.

We grade the evidence weak because most studies are small lab experiments, and there is no good evidence about the long-term health effects of regular napping. Some large studies link frequent long daytime naps with health problems, but that is likely because people who are unwell nap more.

Why do long naps make you groggy?

After about 20 to 30 minutes, you are likely to drift into deep sleep. Waking from deep sleep causes “sleep inertia”: grogginess, slowness and confusion that can last from a few minutes to half an hour. A short nap keeps you in lighter sleep. A nap of around 90 minutes takes you through a full sleep cycle and may avoid waking from deep sleep, but is much more likely to affect night-time sleep.

Do naps affect night-time sleep?

They can. A nap reduces sleep pressure, the drive to sleep that builds while you’re awake. A long nap, or one late in the afternoon, can leave you less sleepy at bedtime. For good sleepers, a short early-afternoon nap is unlikely to matter.

What if you have insomnia?

Avoid napping. The NHS advises not sleeping in after a bad night, and CBT for insomnia asks people to avoid naps, because keeping sleep pressure high helps you fall asleep and stay asleep at night. If you are so tired that you might fall asleep at the wheel or at work, a short nap is safer than pushing through: safety comes first.

How to nap well

• Keep it to 10 to 20 minutes. Set an alarm.
• Nap in the early afternoon, not after about 4pm.
• Lie down somewhere quiet and dim.
• Give yourself a few minutes to come round before driving or doing anything demanding.