The Best Time To Nap For Your Body Composition, According To New Research

I love a nap, but I’ve always thought the biggest question was how long I could sleep without waking up groggy or messing with my bedtime later that night.

Apparently, duration may only be part of the equation.

We’re learning more and more about how closely our daily habits interact with our circadian rhythms, and sleep is obviously no exception. Yet while we spend plenty of time talking about when to go to bed and wake up, there’s been much less attention on when we sleep during the day.

The researchers didn't simply ask participants to remember how often or when they usually napped. They analyzed 159 adults from two separate groups, including 90 adults in Spain and 69 in the U.S. Participants wore actigraphy devices, which allowed researchers to objectively estimate several aspects of their siestas, including what time they started, how long they lasted, and how frequently people napped.

They then compared those patterns with measures of body composition, including BMI, waist circumference, body fat percentage, and muscle mass percentage.

The Spanish group was a little older, with an average age of 52, and was mostly women. The U.S. group was younger, averaging 31, with women making up about 63% of participants. It's worth noting that the strongest findings came from the Spanish group. The U.S. results generally pointed in the same direction, but they weren't strong enough to reach statistical significance.

When researchers combined the results from both groups, people who tended to nap later in the day also tended to have a lower BMI, less body fat, a smaller waist circumference, and a higher percentage of muscle mass.

The connection was especially clear in the Spanish group. For every hour later that someone started their nap, researchers saw more favorable body composition measures. Among women, later naps were also linked to having a higher percentage of muscle mass.

The biggest difference showed up when researchers compared the earliest and latest nappers. People who started their siestas between about 4:12 and 5:42 p.m. had a BMI that was nearly 4 points lower than people who napped earlier in the day.

The researchers didn't just look at what time people napped. They also looked at how long and how often they did it.

In the Spanish group, longer naps were associated with nearly four times the odds of having overweight or obesity. There were also hints that people who napped more frequently had less body fat and more muscle, although those findings weren't strong enough to be considered statistically significant.

I think this is an important distinction because we tend to talk about napping as one single habit. But taking a 20-minute nap a few afternoons a week is very different from regularly sleeping for two hours in the middle of the day. Timing, duration, and frequency could each have their own relationship with our health.

We don't know enough yet to say exactly what the "perfect" nap looks like, but studies like this are starting to give researchers a much better idea of what to investigate next.

I wouldn't rearrange your afternoon around a 5 p.m. nap based on this study, especially if sleeping that late makes it harder for you to fall asleep at night. Getting enough high-quality nighttime sleep should still be the priority.

Instead, I think the more useful takeaway is that there may be more to napping than simply whether you do it. We already pay attention to the timing and consistency of our nighttime sleep, and this research suggests daytime sleep may deserve some of that same attention.