Good news: feeling tired in heat is a sign your brain is working well

If you find yourself drifting off in the middle of a warm day and struggling to nod off at night, it might not be as detrimental as you think. A new study has discovered that heat impacts our sleep-wake cycles and there’s a very good reason for it.  

We’re big advocates of a nap here at Strong Women. Whether it’s dozing on the sofa, snoozing on top of the duvet so as not to fall victim to the nap-turned-three-hour-sleep or having a little shut-eye on the Tube, naps are important.

There’s nothing wrong with feeling like you want to close your eyes for a few minutes during the day. In fact, a new study has found that napping can actually make us more productive at work (which explains why workers at Google have those nap pods). What we’re not so keen on, though, is the kind of weary fatigue that comes with the warmer weather.

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It’s one thing to nap while on holiday or chilling over the weekend, but it’s quite another when we’re trying to get through a pile of paperwork or gear ourselves up for a HIIT workout. But what’s worse, is that even if we manage to side-step the midday snooze, when it gets to our actual bedtime, it’s near impossible to get to sleep.

We end up tossing and turning, flipping our pillow onto the ‘cooler’ side every five minutes and getting up to check that the window is still open because the lack of breeze is turning us into a sweaty mess. 

The solution? Take an afternoon nap. At least, that’s if you believe the findings of a new study that’s found having a midday nap while battling the warm weather is hard-wired into us. 

Why does warm weather make us so tired?

The temperature impacts our sleep-wake cycle, which is why we struggle to nod off during hot summer evenings and stay awake during the day but still struggle to get out of bed when it grows colder. But it’s only recently that we are beginning to understand why this happens, and it’s thanks, in part, to a new study carried out by Northwestern University neurobiologists. Published in the journal Current Biology, researchers found that fruit flies are pre-programmed to take a nap in the middle of the day.

“Changes in temperature have a strong effect on behaviour in both humans and animals, and offer animals a cue that is time to adapt to the changing seasons,” said Marco Gallio, associate professor of neurobiology at the Weinberg College of Arts and Sciences. 

“The effect of temperature on sleep can be quite extreme, with some animals deciding to sleep off an entire season – think of a hibernating bear – but the specific brain circuits that mediate the interaction between temperature and sleep centres remain largely unmapped.”

You’re hardwired to feel tired on warm afternoons

But why fruit flies? In what way could they predict our behaviour? Well, it turns out that they are a particularly good model to study big questions such as “Why do we sleep?” and “What does sleep do for the brain?” because they don’t attempt to disrupt instinct in the same way humans do when we pull all-nighters, for example. They also allow researchers to study the influence of external cues like light and temperature on cellular pathways.

In the newly published paper, researchers found that brain neurons receiving information about heat are part of the broader system that regulates sleep. So, when the hot circuit, which runs parallel to the cold circuit, is active, the target cells that promote midday sleep stay on longer. This results in an increase in midday sleep that keeps flies away from the hottest part of the day. In short, when your body is willing you to go for a snooze, it’s trying to protect you, not derail you. 

Your circadian rhythm is impacted by changing temperatures

The question is: what does this really mean for us in layman’s terms? We asked sleep expert Dr Katharina Lederle, founder and head of sleep health at Somnia, to walk us through it.

“The rhythm of alertness (and sleepiness – but that is doing the opposite) has two dips across 24 hours: one at night and the other in the early afternoon,” she explains. “This afternoon dip might have evolved because that’s when the environment our ancestors developed in was at its hottest – and most dangerous (apart from the night, of course). So, to ensure survival, it makes sense to get into the shade.

“Most African animals do it too. I worked with meerkats in the Kalahari a long time ago; they all just lie in the shade most of the afternoon during the summertime,” she adds. “And since there isn’t much to do, you may as well rest. So, there could be an underlying biological mechanism which is a mix of temperature and sleepiness driving our behaviour to have a nap. And on top of that, certain (warm) cultures have built on that and ‘invented’ a siesta.”

Why you should nap if you’re tired

The problem is we don’t live in a culture that embraces the siesta… yet. So what we really want to know is how can we work around this to help aid our body’s sleep-wake cycle and get as much good-quality sleep as possible.

“The sleep activist in me says, ‘Well, follow your body’s lead and slow down in the early afternoon. We are not machines. We can’t work 24/7’,” Dr Lederle tells Stylist. “We are human beings who need rest – during the day and more so at night. And this new research might be pointing in exactly that direction when they say: ‘There actually might be a very strong underlying biological mechanism that is overlooked in humans.’”

Crucially, she advises that we should see sleep as a powerful tool to enable us to perform well and be healthy, and if this means working in a 20-minute nap on our lunch break to compensate for lost sleep at night so that we can actually maximise our productivity, then so be it.

Especially with many of us still working from home at least a bit more than we used to, carving out a quick nap within our lunch break should be slightly easier than it once was. Other than that, we can only hope our managers read this article soon – perhaps Google’s sleep pods might become the norm. Now that’s a world we want to live in. 

Images: Getty

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