Siesta Science: Is It Better To Nap On Hot Days?

It’s Q&A Day at 10almonds!

Have a question or a request? We love to hear from you!

In cases where we’ve already covered something, we might link to what we wrote before, but will always be happy to revisit any of our topics again in the future too—there’s always more to say!

No question/request too big or small 😎

❝You said not to exericse too much in the middle of the day when it’s hot, good advice but is it good to sleep in the day ie a nap during the hottest part? Or would that just make it even harder to sleep at night?❞

If you’re experiencing extreme heat where you are, then (assuming you are otherwise healthy) that heat is likely the main threat to your health at this time, which means many other health-related considerations can take a back seat where necessary.

That doesn’t mean just abandon other healthy practices if you can reasonably (safely!) keep them up, but it does mean that if your choice is between ruining your average step count and getting heatstroke, please ruin your average step count. You can always get better numbers later, but to do that, you have to not die of heatstroke first.

See also: Stay Safe From Heat Exhaustion & Heatstroke!

As well as more specific-to-some-people factors, such as: The Common Meds That Make You Much More Susceptible To Heatstroke and Beat The Heat, With Fat

You asked about sleep though, so let’s get on to that more specifically…

Daytime sleepiness is itself a health risk

…especially when coupled with difficulty sleeping at night.

Which is a problem, because extreme heat tends to promote both things (daytime sleepiness and difficulty sleeping at night)

For example, researchers (Dr. Slobodanka Pejovic et al.) found that adults who experience both excessive daytime sleepiness and difficulty falling asleep have a substantially higher risk of developing high blood pressure than those with either problem alone.

Note: “excessive daytime sleepiness” was defined as an inability to stay awake and alert during normal daytime activities, including moderate-to-severe daytime sleepiness or irresistible sleep attacks (i.e. surprise naps).

In numbers:

Excessive daytime sleepiness alone was associated with:

• 52% higher risk of already having hypertension.
• 74% higher risk of developing hypertension during follow-up.

Excessive daytime sleepiness and an objectively measured sleep-onset latency of 30 minutes or longer had:

• More than 2x the risk of existing hypertension.
• More than 2x the risk of developing hypertension over time.

Speaking of numbers, this was from a respectable sample size (and a good methodology): Dr. Pejovic and her team analyzed data from 1,741 adults, and the 786 participants who did not have hypertension at the start of the study were followed for an average of 7.5 years to determine who developed high blood pressure. Further, every participant underwent an overnight eight-hour sleep study using polysomnography, allowing researchers to objectively measure how long it took them to fall asleep.

You can read this study, here: Excessive Daytime Sleepiness and Prevalent and Incident Hypertension: The Modifying Effect of Objective Sleep Disturbance

As to whether intentional napping can combat this, science seems to suggest that for most people on average neither helps nor harms:

❝Most research suggests that daytime naps do not have a substantial impact on subjective or objective nocturnal sleep, despite sleep hygiene recommendations to avoid naps❞

Learn more: A systematic review of ambient heat and sleep in a warming climate

However, you are not most people, and averages can be misleading (if it helps some people and harms others, a mean average will say it neither helps nor harms; most well-constructed studies account for this, but nuance in individual studies can get lost in large research reviews)

For example:

❝A few exceptions do exist, reporting that, in older adults, daytime napping is associated with more self-reported sleep problems and greater actigraphy-assessed WASO and fragmentation and lower SE.

Others have found that implementing a daytime napping schedule does negatively impact PSG-assessed sleep. Monk and colleagues compared the sleep of older adults following counterbalanced assignment to two weeks of afternoon napping for 90 min/day and two weeks of sedentary control. Self-reported sleep did not differ between the two conditions, but PSG-assessed sleep following the nap condition was worse in comparison to sleep following the no-nap control.❞

PSG = polysomnography
SE = sleep efficiency
WASO = wake after sleep onset

So in other words, if you fall into the (not clearly defined here, likely due to the heterogeneity of studies using slightly different benchmarks) category of “older adults”, it may be better to not nap if you can reasonable avoid it.

Source: The role of sleep hygiene in promoting public health: a review of empirical evidence

Want to nap anyway?

We’re not the boss of you!

However, to get the best out of napping. There are some more things to take into account:

You probably have experienced the difference between:

• “I napped and now I have energy again” and you continue with your day
• “Darkness took me, and I strayed out of thought and time. Stars wheeled overhead, and every day was as long as the life age of the earth—but it was not the end.” and now you’re not sure whether it’s day or night, whose house you’re in, or whether you’ve been drugged.

These two very common napping experiences are influenced by factors that we can control:

How To Nap Like A Pro (No More “Sleep Hangovers”!)

If you still prefer to not risk napping but do need at least some kind of refreshment that’s actually a refreshment and not just taking stimulants, then you might consider this practice (from yoga nidra) that gives some of the same benefits of sleep, without actually sleeping:

Non-Sleep Deep Rest: A Neurobiologist’s Insights

Take care!