As a sleep doctor, I am often asked about the pros and cons of napping. In our sleep-starved society the detrimental effects of sleeping too little are often discussed. Could an extra helping of shut-eye during the day help us catch-up? Thankfully, nature is kind and allows us to answer this question.

The amount of sleep we need as individuals is genetically determined. Humans are one of the few animals that generally sleep in one shot, however one day’s “dose” can be taken at different times and in several sessions. In fact, the tendency to sleep all the way through the night may be cultural as much as biological. In the pre-industrial era, sleep at night was taken in two periods, one from dusk to 2-3 am, and after an hour or two of wakefulness, another sleep until dawn, so-called “double sleeping.”

These days, even though most of us set out to sleep through the night, many of us still find it difficult to do so, with sleep deprivation resulting in a host of problems both physical and mental. Given these difficulties, a nap may be truly therapeutic. On the physical side is evidence from a 2002 study from the Harvard School of Public Health, of 23,000 Greek adults, which found that those who regularly took a siesta were more than 30% less likely to die of heart disease. In another study by NASA, alertness was increased after a 40 minute nap, and even a 20 minute nap was shown to be more effective than a hefty dose of caffeine.

Every day, more and more careers are putting napping to use. It’s now a regular part of a long haul pilot’s routine. It is also recommended in the UK’s driver’s handbook as an antidote to dozy driving. Enhanced learning may also be a by-product, since memory is consolidated in non-REM sleep.

Napping can increase alertness, reduce dozy driving, and maybe even improve moral awareness

By contrast, when lacking sleep, judgment may be impaired. Google Trends data across six years highlighted a national dip in web searches for moral (but not other) topics on the Monday after the Springtime change, i.e., after an hour’s less sleep, suggesting that a lack of sleep leads to a low moral awareness.

So napping can increase alertness, reduce dozy driving, and maybe even improve moral awareness, but is there an ideal time to nap? The internal drive to sleep, the circadian pressure, is highest at 4-5 am and 3-5 pm (when road traffic accidents are at their peak). So if we choose to sleep less at night, a nap in the mid-afternoon is often a good way to make up the difference. An experiment of nature that illustrates this is perhaps the siesta. In hotter climates, it is useful to remain awake in the cooler evening and to stay out of the sun in the afternoon whilst napping.

The type of sleep we get from a nap may be different than the sleep we get at night, with more REM sleep at night. The reasons for this are that the first third of our sleep period is usually restorative non-REM sleep and the last third is more likely to be predominantly REM sleep. A shorter night’s sleep may therefore consist of more non-REM, as would a nap.

And how long should that nap be? A short nap (less than 30 minutes) during the day will likely be refreshing, whilst longer sleep in the day leads to a deeper sleep, but results in something called sleep inertia or sleep drunkenness upon waking. The National Sleep Foundation recommends a short nap of 20-30 minutes “for improved performance without leaving you feeling groggy or interfering with nighttime sleep”.

History is full of famous nappers, these storied afternoon-slumberers include Leonardo Da Vinci, Winston Churchill, John Kennedy, Napoleon Bonaparte, Ronald Reagan, Lyndon Johnson, Thomas Edison, and Yogi Berra who once said, “I usually take a 2 hour nap from 1-4 pm.” He wasn’t very good at math, but he sure was great at baseball.

Sadly, napping at work may still be a byword for laziness, but in our 24/7 society, maybe more needed than ever.