Sleep has been a nemesis of mine for as long as I have been an adult. Thankfully, my recovery journey with bipolar disorder has led me to discover some powerful tools for higher-quality sleep — and it’s a joy to share them here with you, one by one.

We’ve explored how exposure to morning sunlight and evening darkness helps naturally unlock better sleep — and why a bedtime routine is useful for adults, too.

Today, we’ll cover an often debated subject: naps. They’re a cultural fixture in parts of the world, and many people swear by them.

Are they good or bad for us — or somewhere in the middle?

As background, our sleep drive is determined by two factors: a) when it is in the day-night cycle and b) our physiologic need for sleep, determined by sleep debt and the day’s sleep-related activities.

One important signal for the latter comes from a molecule called adenosine, which builds up in the lower forebrain over the course of the day and induces sleepiness via the ventrolateral pre-optic area. Our sleep drive is usually highest in the middle of the night and there is a smaller bump in the late afternoon. Caffeine transiently opposes the effects of adenosine and good-quality sleep reliably depletes adenosine.

So: a high level of adenosine (among other mechanisms) promotes sleep drive and sleep at any time of day decreases adenosine levels. This means that a nap in the middle of the day drives our adenosine levels down, leaving us with less at bedtime — we therefore feel less sleepy at night after a daytime nap.

If you’re someone who struggles with nighttime sleep in any way, one of the most high-impact changes you can make is to eliminate daytime naps to ensure you have a stronger sleep drive and higher-quality sleep at night. I can personally attest to how well this principle works, having stuck to it for the majority of my adult life — including early parenthood — with excellent results.

However, if you are in the sleep elite — meaning you have no trouble falling and staying asleep at night — you may be able to derive benefits from a brief afternoon nap. In healthy, young volunteers who had no difficulty sleeping at night and were not habitual nappers, after a night of shorter sleep (five hours), an afternoon nap of 10 to 20 minutes was found to boost alertness and cognition, with effects starting immediately after the 10-minute nap (thought to be the best period of time) and discerned up to 155 minutes post-nap.

Naps of 30 minutes or longer resulted in transient periods of sluggishness and impaired performance, called ‘sleep inertia.’ Most people will know exactly what this feels like.

It’s worth noting that compensating for lower nighttime sleep with daytime naps is not a perfect stand-in — the body prefers one long period (nine hours, in the study cited) of sleep at night to multiple naps throughout a 24-hour period, in terms of measures of sleep debt and homeostasis.

Morning or early afternoon naps are mostly spent in lighter sleep stages and naps later in the day, after about 3 p.m. (varies depending on factors like your chronotype and sleep routines), when your sleep drive is greater, are comprised of deeper sleep stages and look more like sleep at night, which can disproportionately displace nighttime sleep.

So if you do nap: do it by the early afternoon and set an alarm for a total nap duration of 10 to 20 minutes. You could even have caffeine right before (as long as this wouldn’t disrupt your night), which will help you emerge from the nap on time.

If you are someone who has trouble sleeping at night and want to avoid daytime naps, one great way to combat that afternoon slump is to step outside and expose yourself to bright light like direct sunlight for up to 30 minutes (or however much you can manage), which has cognitive benefits on par with brief afternoon naps. Or use that slump to exercise.

Associations between napping and overall health are all over the map, and cannot currently be summarized cleanly or used to draw casual claims, but I want to mention them to be complete.

On the pro side: in one study, people who napped once or twice a week had fewer cardiovascular events than those who never napped, with no benefits found for more frequent nappers. In another, habitual nappers had lower odds than non-nappers of brain aneurysm rupture. On the con side: daily daytime napping has been associated with numerous health conditions ranging from diabetes to obesity to metabolic syndrome to non-alcoholic fatty liver disease.

Implications and causal inferences are still under study.

The bottom line: If you struggle with nighttime sleep, eliminate daytime naps and see if this opens up better sleep drive and quality.

If you sleep well at night, try restricting naps to 10-20 minutes to eliminate sleep inertia and see if you feel better.