Is a daytime power nap healthy or not?

A nap averaging 55 minutes early in the afternoon provides a small to moderate boost to alertness, memory and concentration, lasting about two hours. This holds across all ages and sexes. However, almost all of this research was conducted in a laboratory setting, so whether the same benefits apply in a typical workplace is not certain.¹

Immediately after waking you may experience sleep inertia: a groggy feeling that temporarily lowers your performance. This passes on its own, but you should therefore not schedule a nap just before a meeting or task. The improvement in alertness only kicks in afterwards.¹

Naps of 30 minutes or longer are a different matter. A meta-analysis of 44 large population studies involving more than 1.8 million participants shows that long naps are associated with higher mortality, more cardiovascular disease and more diabetes. Naps under 30 minutes do not show this elevated risk. Because these are observational studies, it is also possible that people who take long naps are already in poorer health.²

Two genetic studies with a combined total of more than 800,000 participants from the UK Biobank make a genuine causal relationship more plausible. People with a genetic predisposition to napping more frequently had higher blood pressure and a larger waist circumference, even after correcting for weight. These are risk factors for cardiovascular disease.^3,4

The same large meta-analysis hints at a benefit of napping in older age: less cognitive decline and less muscle weakness. However, the evidence is limited and a causal relationship has not yet been established. The advice to avoid naps in order to improve night-time sleep is, incidentally, less well supported than it sounds; outside the clinic it has barely been tested. People who sleep well at night do not necessarily need to cut out a short nap of under 30 minutes.^2,5