This summer brought heat waves across the globe.
In some countries, the heat waves were the worst in history.
You’ve also probably noticed that you can’t sleep very well when temperatures are unbearable.
How do heat waves affect sleep, and is there anything you can do about it?
Read on to learn more and find out seven tips to keep cool when it’s too hot to sleep.
Why can’t I sleep when it’s hot?
Hot summer nights disrupt sleep because they affect melatonin. Melatonin is a hormone that regulates your sleep and wake cycles. This important hormone, made by the pineal gland, promotes sleep by reducing the body’s core temperature.
The body produces melatonin between 10 pm and 5 am. More precisely, secretion of this hormone increases after the onset of darkness and peaks in the middle of the night, around 2 am to 4 am. Then, melatonin gradually decreases during the second half of the night (1).
Hot temperatures interrupt this process, meaning the body cannot produce sufficient amounts of melatonin to reduce core temperature. This is particularly the case when humidity is high.
When the body doesn’t produce enough melatonin, it’s not easy to fall asleep. But there are other reasons you can’t sleep when it’s hot. Dehydration, difficulty breathing, constant sweating, and uncomfortable clothes are also important factors.
How heat waves are messing up your sleep
Hot summer nights are one thing, but a heat wave is something else entirely. A heat wave is defined as an extended period of abnormally hot weather.
In order to be considered a heat wave, the temperatures need to be outside the historical average in a specific area. A heat wave is not a “typical” summer thing; it’s a dangerous phenomenon.
A study published in JAMA Network Open found that between 2008 and 2017, extreme heat contributed to 13,000-20,000 deaths. Most deaths occurred due to heart disease (2).
The impact of heat waves on your sleep is more pronounced than on a typical summer night. Heat waves mess up your sleep because they have a detrimental impact on core body temperature and melatonin levels.
Heatwaves affect deep sleep
Our brain goes through four stages of sleep such as awake, light sleep, deep sleep, and rapid eye movement (REM) sleep. It cycles through these stages for about 90 minutes and repeats each cycle four to six times per night.
Deep sleep is very important here because it slows down brain activity and breathing. This also allows the brain to consolidate memories.
Also known as slow-wave sleep, deep sleep is sensitive to temperature. This part of your sleep cycle benefits more from cooler rather than warmer temperatures.
Heat waves make it more difficult to regulate body temperature. Under ideal circumstances, the body temperature starts falling one to two hours before bedtime as your body prepares for sleep. The body temperature continues to drop while you’re sleeping. This natural internal cooling effect allows us to enter the deep sleep phase.
That said, high ambient temperature, such as during heat waves, prevents the body temperature from falling quickly enough to induce sleep. Not only does it prevent you from falling asleep, but it also causes frequent awakenings throughout the night.
As a result, you can’t achieve the deep sleep phase. If you’ve ever wondered why you wake up tired in the morning, this is the answer. Deep sleep is vital for waking up energized and refreshed.
Heatwaves affect REM sleep
Besides negatively affecting deep sleep, heat waves also affect the fourth stage (REM sleep).
A study from the Science and Technology for the Built Environment found that higher temperature in the bedroom was strongly linked to shorter REM sleep duration (3).
Interruption of REM sleep means the whole cycle must start again. As a result, the REM phase can’t do its job. The importance of REM sleep is in stimulating brain areas essential to learning and forming or retaining memories.
Heatwaves affect mental health
Unbearable temperatures harm our physical and psychological health. For that reason, a heat wave can worsen mental health, especially in persons with a specific condition such as depression.
For instance, a study from the Environmental Health Perspectives revealed that above a threshold of 80°F (26.67°C), there was a positive link between ambient temperature and hospital admissions for behavioral and mental disorders. During periods of heat waves, hospital admissions increased by 7.3% (4).
The biggest reason for the worsening mental health during heat waves is lack of sleep. However, the relationship between sleep and mental health is a two-way street.
One influences the other. Sleep-related problems such as insomnia can also be a symptom of some mental health problems, such as depression.
In other words, if your sleep pattern is out of control during heat waves, your mental health condition could be a major factor here. Of course, this applies to persons who have a certain mental health problem.
How hot is too hot to sleep safely?
As seen above, heat is a major disruptor of REM sleep. Generally speaking, a bedroom temperature over 70°F (21°C) is considered too hot to sleep safely. If the temperature climbs above 77°F (25°C), you’re bound to struggle to fall or stay asleep.
The ideal temperature for sleeping is between 60°F (16°C) and 64°F (18°C). It’s important to keep in mind that even though temperatures do drop during the night outside, sometimes they can still reach 86°F (30°C) in bedrooms. Therefore, it’s important to be careful and take necessary measures to ensure healthy, much-needed sleep during hot summer nights.
7 tips to get to sleep when it’s too hot
While heat waves can wreak havoc on your quality of sleep, there’s a lot you can do to still get enough good night’s rest.
Below, you can find useful tips for sleep when it’s too hot.
1) Avoid cold showers before bed
For most people, there’s nothing more relaxing than taking a cold shower before jumping into bed. If you also tend to do so, it’s time to stop.
Although a cold shower will reduce your core body temperature, it isn’t likely to help you get enough sleep. In these circumstances, the cold water could act as a shock to your body and thereby keep you awake longer.
Immersing the body in cold water increases the levels of cortisol and norepinephrine. Cortisol is a stress hormone and is also involved in boosting alertness.
Generally speaking, cortisol levels drop while you’re preparing for sleep, but a cold shower could mess up its “schedule.”
2) Use a lightweight bedding
Probably the easiest thing to do for a better quality of sleep on hot summer nights is to use lightweight bedding. You should do so, even if you are tempted to sleep without any covering.
Use a summer comforter or a light sheet instead of something heavy or bulky. It will help you regulate your body temperature more effectively.
Lightweight bedding allows you to move freely, and you can always kick out your arm or leg to cool down if necessary.
3) Stay hydrated
Sometimes despite doing your best, the room temperature isn’t dropping. In these cases, the body looks for a different way to cool down.
That usually means a lot of sweating. As you keep sweating, it can be even more difficult to get enough sleep.
That’s why you need to stay hydrated. Make sure to keep water beside your bed and take a few sips now and then.
Replenishing the liquid you’re losing is important for overall health, but it can also help with your body temperature and better sleep.
4) Cool down your bedroom
While this may seem like a no-brainer, it’s impossible to leave it out. Cooler environments lead to a better quality of sleep. For that reason, you should do everything you can to cool down your bedroom.
Keep hot air out by closing blinds and windows during the hottest period of the day. Get curtains if you don’t have them.
If you have A/C, it’s easy to cool down the bedroom. Since some people get a headache from A/C, you can avoid it by setting a reasonable temperature.
On the other hand, if you don’t have A/C, you may want to sleep in a room that is cooler than your bedroom.
For example, some people may realize their living room is cooler than the bedroom, which means they can sleep there when heat waves come along.
5) Get some breeze
An air conditioning unit could be helpful to promote air circulation and thereby help regulate your body temperature. But, if you don’t have it, a fan could help.
Make sure not to place the fan near your head, though, to avoid problems with dry mouth, nose, and throat.
You can also open windows in the evening, pending the temperature is lower than it was during the day. This could still promote air circulation to some extent.
6) Consider sleeping on the ground
Sleeping low to the ground is a lot cooler than sleeping on the bed. You may want to consider getting a futon that you can use to sleep during heat waves.
Futons are easy to store, clean, and wash. Plus, futons are also good for your back and spine.
7) Remember what to avoid
In order to improve the quality of sleep during hot summer nights, there are some things to avoid.
- Exercising close to bedtime
- Chocolate and caffeinated beverages
- Hot, heavy, or spicy meals (especially near bedtime)
- Participating in too many activities (it builds up heat)
Keeping cool during the summer
Staying cool during summer can be challenging but not impossible. These tips can help you out:
- Wear loose, lightweight clothing made of natural, breathable materials
- Avoid wearing clothes with dark colors; opt for lighter colors instead
- Wear a hat
- Drink plenty of water even if you don’t feel thirsty
- Take a cold shower or bath (you can during the day, but avoid doing so before bedtime)
- Apply ice bags or cold washrags on your neck and wrists
- Close the door of unused rooms
- Cook in the morning, preferably outside, or use a slow cooker, but make sure to limit the use of a stove or oven.
- Treat yourself with ice cream or popsicles.
- Avoid going outside during the hottest time of day (between 10 am and 4-5 pm)
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Heat waves mess up your sleep because they affect melatonin and body temperature and disturb your deep sleep as well as the REM phase.
Fortunately, you can improve your quality of sleep by avoiding cold showers close to bedtime, closing windows and blinds during the hottest time of day, and keeping hydrated. Consider sleeping on a futon or in the coolest room in your house or apartment during the heat wave.