Too Hot To Sleep? Here’s Why

Too Hot To Sleep? Here’s Why

Bushfires are quite appropriately dominating our nation’s concerns during the current Australian heatwave. But for many, the struggle to sleep through soaring temperatures is a personal inferno that dominates conversation around offices and homes across the country.

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Sleep and body control of temperature (thermoregulation) are intimately connected. Core body temperature follows a 24-hour cycle linked with the sleep-wake rhythm. Body temperature decreases during the night-time sleep phase and rises during the wake phase. Sleep is most likely to occur when core temperature decreases, and much less likely to occur during the rises.

Our hands and feet play a key role in facilitating sleep as they permit the heated blood from the central body to lose heat to the environment through the skin surface. The sleep hormone melatonin plays an important part of the complex loss of heat through the peripheral parts of the body.

MORE: Heatwave: How To Cope With Australia’s Extreme Summer Temperatures

At sleep onset, core body temperature falls but peripheral skin temperature rises. But temperature changes become more complex during sleep as our temperature self-regulation varies according to sleep stage.

Research has shown how environmental heat can disturb this delicate balance between sleep and body temperature. An ambient temperature of 22˚ or 23˚ Celsius is ideal. Any major variation in this leads to disturbance of sleep with reduced slow wave sleep (a stage of sleep where the brain’s electrical wave activity slows and the brain “rests”), and also results in less dreaming sleep (rapid eye movement or REM sleep).

Indeed during REM sleep, our ability to regulate body temperature is impaired so in a clever sort of way the body “avoids” this stage of sleep during extreme cold or heat. A heat wave may cause several nights of fragmented sleep with less slow wave and REM sleep. This will certainly cause a correct perception of bad, restless sleep with consequent negative effects on mood and alertness.

In theory, it may also have subtle effects such as problems with complex memory retention, higher judgement (poorer decision making and increased risk-taking behaviour), blood pressure control and regulation of glucose in the body. The clear message is this: if you’re going to make some big decisions during a heatwave, sleep in a carefully controlled air-conditioned environment.

But apart from air-conditioning, what can you do to sleep better during a heatwave? Sleeping in the lateral position (on your side) with less contact with the mattress may be good but the body tends to do this anyway during sleep, in response to rising temperatures.

Cooling the central body with a wet cloth or towel makes sense. A cool shower may also help. It is important to avoid doing anything too strenuous in the hours before bed-time as this will make it harder for the body temperature to fall during sleep. And when you wake up hot, sticky and irritated because you don’t have air-conditioning or believe such devices are environmentally unsound, remember those fighting bushfires – it could be a lot worse.

Ron Grunstein is Professor of Sleep Medicine at University of Sydney. He receives funding from the National Health and Medical Research Council.

The ConversationThis article was originally published at The Conversation. Read the original article.


  • If this is true, that any temp different than 24c is a problem, then how have human beings successfully lived for thousands of years in climates where these temperatures are extremely rare?

    I’m sorry but I think these conclusions are wrong.

      • Sorry, but if your BODY temperature was 24C you’d be dead. Human body temp is about 37C.

        It doesn’t need to deviate from this very much to kill you. For example 37.7 is considered a fever, 40C or greater is hyperthermia and life threatening and 35C or below is hypothermia and also life threatening.

    • And you’re a professor of sleep medicine too, are you? Great if you want to exercise a little independent thought, but at least try to understand what the good professor was saying before you wade in and flatly contend his conclusions. As it is, nowhere in the article does it say that sleeping outside of this low 20s temp range is problematic. He said the ambient temp at this range is IDEAL for achieving optimal sleep – that is all. Furthermore, I would imagine that humans from all cultures subconsciously recognise this and implement strategies to achieve sleep as close as possible to this temp range as possible – in the design of the homes, the modes of dress, and so on. Inuit people don’t tend to sleep naked on the snow, just as those in the tropics don’t design their dwellings to be isolated from the cooling evening breeze. So by and large, I think most humans would probably sleep close to these ideal temp ranges. It’s only those weather extremes that occasionally hinder our ability to do so effectively (essentially the point of the professor’s article).

      • Lol. At least you’re thinking. Unfortunately it seems you’re only thinking what you’ve been told to think but whatever.

        I’m glad my attempt at independent thought excited you. Maybe you might want to attempt some independent thought of your own one day?

        PS. Many place don’t even get down to 24c at night. Or ever get up to 24c during the day. People still live there. According to the article, that means “In theory, it may also have subtle effects such as problems with complex memory retention, higher judgement (poorer decision making and increased risk-taking behaviour), blood pressure control and regulation of glucose in the body.”

        It goes on to say this:
        “The clear message is this: if you’re going to make some big decisions during a heatwave, sleep in a carefully controlled air-conditioned environment.”

        Which made me laugh. There are countries where a big percentage of the population will NEVER have access to airconditioning. The human body is an amazing mechanism. It would not have evolved to effectively root so many millions of people who cannot cool their ambient temperature to 22 or 23c when they sleep.

        So in my opinion, the science is leading this man’s thought processes. I wonder what populations he does his research on? Could that be skewing his results? Just because he has letters after his name, doesn’t mean you have to blindly accept his findings, or worse yet, wade into battle to defend his article about something you likely have almost no interest or experience in!

        But it’s your life so whatever. Good luck with your independent thoughts now that I’ve shown you how it’s done.

        PPS. I could be wrong. 😛

        • Rowan, the point I was making in the previous post – which you have obviously missed – is that humans seek to regulate or control ambient temperatures during their sleep cycles (at least as much as it is possible). This was in rebuttal to your assertion that people living in a wide range of environments could not account for the consistent 24c temps the prof mentioned as being optimal for sleep. So I’ll say it again. Humans have the capacity to implement measures to withstand a variety of environmental challenges and climatic conditions. If it is snowing, they don’t just say “bugger it, I’ll camp here in my undies”. As a fellow commenter pointed out, they’ll throw on a blanket – or a fur – or add more layers – or build a shelter – or make a fire. By doing this, they would be working to achieve conditions approximate to those outlined by the professor. In warmer environments, they’ll implement different strategies – perhaps mostly pertaining to the design of their housing. Deserts tend to be cool at night anyway, and tropical/equatorial regions tend towards minimums of approx mid 20s (from what I remember of my own experiences being raised in the tropics, as well as a brief, and admittedly internet-based, flurry of research). In any case, people use their technology and other means to adapt to their environment. One of the tools we use in our affluent society to keep cool is air con – just as one of the methods used by villagers on the Sepik River would be to design their homes on stilts over the water to take advantage of evening breezes. Now although I agree with you that the assumption of being able to access air con is a little ethnocentric, in the professor’s defence, he probably didn’t have it mind that his target audience for this article might be a family living on the Pantanal or on a Namibian savannah. So as a tool available to many of us to utilise in achieving a good night’s sleep, the writer’s suggestion remains valid.

          The point is, again, that I accept the professor’s assertions of these temps being ideal for human sleep patterns, and that it is human inventiveness and adaptation that allows for people to modify their environments to conform with this biological ‘characteristic’. And I’m sorry you think I’m an unquestioning lap-dog of the scientists, but I tend to agree more with people who have put the effort into understanding something than with those who don’t. I’m quirky in that regard.

          • Which I have obviously missed?

            I’m sorry, you’re just some random on the internet so I don’t care to keep this going. Well done on researching stuff though. I would never have gone to the effort.

            It’s more your tone that I don’t like. What’s with all the veiled insults and ‘better than you’ tone? You might want to think about why you feel the need to type with that personae. Is that really the kind of person you want to be? A know it all dipshit who laughs at those with lesser understanding of esoteric subjects?

            If so then I leave you to it.

    • It say that 22 to 23 degrees is ideal, it doesn’t say required.
      There is a big difference between ideal and required in the English language and its application in this article.

  • I read recently a good night sleep can be contributed to a room temperature between 16-22c (If i remember correctly I read this on either Gizmodo or here at LH.

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