How to counteract the harmful effects of high temperatures on sleep?

France is suffocating. The second heatwave of the year in France reached its peak this Monday over a large part of the country, warns Météo-France, which is calling on residents of 40 departments on orange heatwave alert, including those in the Ile-de-France region, to protect themselves.

This Monday, the thermometer climbs to 36 to 38°C in the Paris region, but also in PACA, in the Center, Burgundy, Upper Normandy and up to Hauts-de-France, according to the weather organization. And with such temperatures during the day, we will also be hot tonight, which is not without impact on our sleep. How to reach the arms of Morpheus without suffering too much from the heat? 20 Minutes explains to you.

“A fragmented sleep”

If the heatwave is logically difficult to bear during the day, when the sun is at its zenith, it is also unbearable at night, when we would like to rest in the cool. And under the effect of global warming, the problem does not seem likely to improve. “The increase in temperatures reduces sleep on a global scale, amplifying the risk of a global sleep debt,” emphasizes National Institute of Sleep and Vigilance (INSV). By 2099, climate change is expected to transform sleep: we could lose between 50 and 58 hours of sleep per person each year, due to non-optimal temperatures. Faced with this threat to our sleep, “three populations are particularly at risk: newborns and young children, the elderly and workers with atypical hours.”

But everyone can see their sleep affected when the temperature is high at night. “The nighttime heatwave will tend to fragment sleep and slow down falling asleep,” confirms Armelle Rancillac, a neuroscience researcher at theInserm and sleep specialist. A major problem when we know that in normal times, many already suffer from sleep disorders.”

However, “body temperature and sleep are very closely linked: to fall asleep, you need to be able to lower your body temperature by 0.5 degrees before going to bed,” explains the researcher. “These are the same neurons that manage the body’s internal temperature and sleep; they are located in the same region of the brain.”

Keep it fresh

But to sleep like a baby, the temperature of the room is a key element: it must not exceed 19 degrees. Easier said than done when the thermometer remains stuck above 25 degrees at night. To achieve this, you must keep your home cool as much as possible.

During the day, “blinds and windows must be closed during their entire exposure to the sun,” prescribes the INSV. And if your home has several windows, alternate opening and closing them depending on their exposure to the sun. Leave your windows open on the shaded side if this allows for drafts. If it is not possible to create drafts with only the shaded windows, keep them closed.”

You can also try to “cool the rooms by evaporating water: place a towel or damp cloth in front of an open window so that the evaporation cools the atmosphere, adds the INSV. Re-wet the cloth as soon as it is dry. Place a block of ice or a bag of ice cubes in a draft or in front of a fan”. Then, in the evening, “when the sun has set and the outside temperature has dropped, open the last windows”, which can be left open during the night. And “for those who have air conditioning at home, I advise against turning it up too high, insists Armelle Rancillac: if it is too cold at night because of the air conditioning, the body will have difficulty getting used to it, which can also disrupt sleep”.

“Beware of external stimuli”

For those who choose to sleep with the bedroom window open, “this can help cool the room, but can create nighttime pollution,” warns Armelle Rancillac. So I recommend sleeping with a blind over your eyes: the more you sleep in total darkness, the better your sleep, especially since in summer, the day rises very early. You can also sleep with earplugs, because sleeping with the window open exposes you to outside noise. However, you have to be careful with external stimuli, especially when sleep is more difficult to achieve because of the heat. Make sure to create your own cocoon, your own bubble to facilitate falling asleep and restful sleep, since sleep is already affected by the heat, and to favor light clothing and a cotton sheet to go to bed.”

With this high heat, “you also have to make sure you stay hydrated,” says Armelle Rancillac. “But be careful, because summer is the season for barbecues and aperitifs, with an increased tendency to consume alcoholic beverages. However, not only does drinking alcohol dehydrate, it increases the body’s internal temperature. And while many people think that it relaxes and can help you sleep, in practice, it further reinforces the harmful effects of the heatwave on sleep, by further fragmenting it.” So if you want to treat yourself while taking care of your health, drink water, and instead opt for non-alcoholic spirits, to cool off in a friendly atmosphere.

“Strengthen your sleep routine”

And while we know that we sleep better in a cool room, when we have sleep disorders, high temperatures can create additional stress and slow down falling asleep even more. “Apprehension and psychological conditioning can affect sleep,” says Armelle Rancillac. “Hence the importance of putting yourself in the right mental conditions to fall asleep. This should not generate additional stress: you can still sleep very well even if it is 26 degrees at night,” reassures the sleep specialist. Of course, this threshold varies from one person to another, depending on age and body mass, but it is possible.”

To achieve this, “you need to strengthen your sleep routine,” she recommends. We talk about it a lot for young children, with the bedtime story ritual. But it’s also important for adults, to allow the brain to become aware that it’s time to slow down.” To do this, common sense measures should be favored (even if many of us know it and don’t do it): “we reduce light intensity, as well as screens, whose blue light delays the production of melatonin, the sleep hormone. This helps reduce solicitations – intellectual, social or other.” Obviously, scrolling on Instagram for two hours in bed is not what will make you fall into the arms of Morpheus at top speed.

And if you like to take a shower before going to bed, “we avoid taking it too cold,” reminds Armelle Rancillac. Because with “cold showers, the body will try to warm up,” adds the INSV. On the other hand, continues the sleep specialist, “we can not dry ourselves too much, because the evaporation of water on the skin will help cool the body,” and thus promote falling asleep.

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