There are hot sleepers, cold sleepers, and the rest of the population who don’t lean towards either, but still know their body temperature changes through the night.
What many people don’t know is that your body temperature can directly impact the quality of your sleep.
In this article, we will explore thermoregulation during sleep, so you can improve your sleep quality.
To understand how and why your body changes at night, you should know that your body changes throughout the day too.
It’s on a 24-hour cycle, almost like a clock-powered thermostat. Your hypothalamus adjusts the thermostat to get to 38 degrees Celcius at some point throughout the day.
The higher your temperature, the more energy you have. You can see an example of this when you work out and find yourself energised—it’s because you heated up your body, and now you get the payoff.
So, let’s say you get up every morning at 6 am. You wake up at about 35.8 degrees. You’re not too hot, and you’ve got a bit to go before you hit that 38-degree goal.
Your temperature slowly rises. By noon you’re getting pretty hot, which is why you may feel energized around lunchtime.
You’re a toasty 37 degrees but from here you may never hit that exact 38. Your body temperature keeps climbing, and you may hit the 38 but around 6 pm you hit your peak and start cooling off.
Once you fall asleep your body keeps cooling, and somewhere between 4 and 6 am you’re at your lowest temperature of the day.
This progression happens to everyone. The time of day influences your core body temperature, which impacts energy. The results have been studied in elite rugby players.
The reason you hit that peak and then fall in the early evening is to prepare your body for bed it gives you the most energy around midday when you need it, and takes it away so you can relax in slumber.
So if your body works during the day to set you up for the night, why does it change during the night too? The main reason is light: no light means sleep time, so your body shuts down a bit. Both your core (internal organs) and shell (skin) temperature get lower based on signals sent by the brain.
We don’t yet know the exact cause behind this sleepy-time cooldown. It remains a mystery of evolution, but scientists, of course, have their theories. Right now, there are two notable theories in play.
Some evidence points to this temperature cycle helping regulate kidney and liver function. So far there are no public studies to back this up, but Journalist Susannah Locke interviewed psychiatry professor Christopher Coldwell for Vox, who stated that even minor changes can help synchronize your cells.
Coldwell goes on to clarify that so far it’s only a theory, with no definitive evidence supporting it.
The second theory relates to your metabolism. When you sleep your metabolism drops by up to 10 per cent, which lowers your body temperature.
The lowered metabolism would have been beneficial in the past when humans were hunter-gatherers. Sleep was a way to spend time not using energy, letting the body survive without food, and letting the brain refresh and replenish its energy without nutrients.
Not only does this stop you from starving, but it gives you time to rebuild energy before you go hunt for food. As most creatures are still hunter-gatherers today, it explains why most animals sleep and it may also explain why we evolved to sleep at night, not in the daytime.
At night the temperature drops, so it makes sense that your body temperature would, too. Plus, it would take more energy to stay awake in the cold of the night so it makes sense to go into conservation mode during this time.
Throughout the night you go through a sleep cycle broken up into four repeating stages. While this question makes a lot of sense as different stages affect the body differently, the stages don’t affect temperature very much.
Your temperature will only rise and drop in relation to time, regardless of what’s happening in your sleep or in your dreams, until REM sleep occurs. Then, your body temperature rises.
Waking up drenched in sweat is a common issue. There could be a number of natural, fixable reasons for this, like:
The first two have nothing to do with your temperature changes throughout the night. The night-time fluctuations relate to your core temperature, where the first two of these factors are about your skin temperature.
Naturally, outside influences causing overheating will make you sweat. There are ways to combat this which we’ll be discussing later in the article, but again, they’re unrelated to sleep stage.
However, one common cause of sweating seems like it may be due to sleep stage.
As frequently as people seem to ask this question, humans don’t actually sleep during REM sleep according to several sleep experts across the web. This claim makes sense. It’s essentially impossible for you to sweat during this stage.
Although it may seem like an uncontrollable instinct, your hypothalamus actually decides it’s time to sweat—and that part isn’t doing so much during REM sleep. In REM sleep you’re paralyzed. The only muscles working are those that it takes to breathe, and your eyes. Your glands aren’t doing anything.
You may be confusing sweating during REM with sweating during a night terror. During night terrors it’s not unusual to wake up terrified, in a clammy or cold sweat or sometimes a hot when.
However, night terrors most often take place during stage three of sleep, which comes before REM. While it’s deep sleep, you’re not paralyzed and your brain function is different than it is in REM.
So, sweating in sleep can occur based on various natural and changeable aspects of life what else is normal?
The first normal part of sleep is that you’ll get colder by about two degrees. Your body doesn’t need energy, so it doesn’t need heat. This is your restoration period and so you cool off.
Your brain temperature drops alongside your body’s, so your internal and external organs are roughly the same temperature, give or take a bit based on your bedding. This temperature drop is gradual, as you cycle from stage one to three, aka NREM sleep. It makes sense both time-wise and sleep-stage-wise.
Despite the temperature drop, your brain is still thermoregulation consciously to make sure you don’t get too cold. If you do get cold based on external factors your brain will likely wake you up, shivering, especially in light sleep.
Unlike other mammals, humans don’t lose their ability to regulate while sleeping. We don’t quite know how difficult it is for the brain to keep the function going, but scientists don’t think it’s too much of a feat—despite how several animals’ body temperatures go well below normal for most of their nights.
So if you’re not getting too hot or cold, what’s the norm? Well, it varies based on the person and external factors, but most of the time you go from around 37 degrees down to your coldest of 36. Anything higher or lower than that and you may be ill.
If you somehow find out you have a temperature under 36 degrees when you wake up, it may be cause for concern and you should at least get checked out by a doctor.
However, so long as you stay at that number or above, it doesn’t matter what time of night it is. In fact, if you notice you’re at your lowest temperature early in the night, it may be a sign that you’re a morning person and are ready to wake up naturally earlier.
As temperature fluctuations are a natural process, it doesn’t seem like it would impact sleep temperature too much. However, a study reveals that temperature is highly important in sleep quality.
In the study, the researchers raised peoples’ body temperatures by less than a degree. The sleepers slept more deeply, woke less often, and these results were highly prominent in elderly sleepers and insomnia sufferers.
The researchers also discovered that narcolepsy sufferers run slightly hotter than the average person, which may contribute to their frequent bouts of sleepiness.
So, therefore, the warmer you are, the better don’t skip that blanket! Especially considering how thermoregulation isn’t difficult to achieve at night, but it’s not as efficient as it is while you’re awake.
This lets external temperature influence you too easily, so you wake up sweating or shivering. It’s also why a cold bedroom when going to sleep feels neutral, but you wake up freezing cold.
Ideally, you want a warm but not uncomfortably hot space, before and during sleep. If you can’t achieve a warmer bedroom consider bathing before bed. It’ll warm you up and make you drowsy, but then you’ll cool off as you dry essentially mimicking how your body cools once you fall asleep.
Your body does a lot of work and will do it regardless of outside influence but you can help it achieve the perfect sleep temperature, based on its natural rhythms and how you tend to sleep.
While hot sleeping is best, you don’t want to be too hot and wake up sweaty and uncomfortable. There are a few things you can consider doing to combat a hot sleeping issue.
Memory foam in particular holds and reflects heat. You want a mattress that can breathe. Consider a memory foam mattress containing activated charcoal, or switch to a different type of mattress completely.
Innerspring mattresses are excellent as the coils contain lots of gaps, letting airflow through the mattress well. Pair this with a slatted bed and there’s room for air to circulate under the mattress, too.
Consider switching to wool sheets or a wool-based mattress topper. Wool is a naturally breathable material that helps regulate body temperature, particularly merino wool.
Bamboo is another fantastic material for breathability and cooling properties, and like wool, it’s wonderfully sustainable. That’s another one to consider if wool doesn’t sound appealing to you.
A fan is a simple solution to an overheating problem. Don’t have it too close to the bed or you might feel it blowing you uncomfortably throughout the night. Have it a few feet away.
Fans not only cool you down, but they can provide a fantastic source of white noise which can also improve your sleep quality.
Cold sleeper? No problem. Your solution is easier. Here are a few suggestions:
Your body is constantly working on thermoregulation during sleep and during waking hours. Sometimes it needs a bit of help if you’re a naturally hot or cold sleeper, so pay attention to the tips above for that.
Remember, going to sleep warmer is better and can improve your sleep quality. But once you’re sleeping you cool off, so always keep an extra blanket handy in case your body decides to get too cool one night.
As always, feel free to leave a comment or question below if there’s anything on your mind regarding thermoregulation during sleep.
Disclaimer – The advice above should not be considered medical advice and is meant to provide an overview of the kind of sleep issues seniors and older people may face. If you are at all concerned about your health, no matter what age, always consult your GP.