Log in
When temperatures drop in autumn and winter, you might find yourself unable to sleep due to cold hands, feet, or body. Using an electric blanket to warm up might make you too hot to fall asleep, or cause you to wake up in the middle of the night. Here, we explain how to get a good night's sleep even on cold days.
Masahiro Nakajima
PhD in Science / CFO, Brain Sleep Inc. / Senior Sleep Health Instructor
Born in Yamaguchi Prefecture in 1983. Graduated from the Department of Physics, Faculty of Science, the University of Tokyo in 2007, and completed his PhD in Physics at the Graduate School of Science, the University of Tokyo in 2012 (PhD in Science). Joined Brain Sleep Inc. as a director at its establishment in May 2019. As CFO, he oversees financial matters and sleep consulting services for partner companies, in addition to conducting sleep research based on the results of sleep-related epidemiological surveys (published as sleep deviation scores) and providing health management support services for corporations. Obtained Senior Sleep Health Instructor qualification in November 2021.
Why can't I sleep when it's cold?
On cold nights, you might have trouble falling asleep even after getting into bed, or you might wake up multiple times during the night even if you do fall asleep. These issues lead to a decline in sleep quality, which can affect your daytime performance and cause drowsiness.
When your core body temperature drops, you feel sleepy.
There's a deep connection between sleep and core body temperature (the temperature inside your body). To sleep comfortably, it's important to lower your core body temperature.
When a person falls asleep, blood flow increases within the skin, raising the surface temperature of the body (skin temperature) on the face and limbs. Heat is then released from the skin, causing the core body temperature to drop.
In other words, the release of heat from the hands and feet lowers the core body temperature, and as the difference between skin temperature and core body temperature narrows, the body switches into sleep mode. Lowering the body temperature also helps the brain enter a relaxed state, making it crucial for good quality sleep.
If your hands and feet are cold, you can't dissipate heat.
Cold air settles at lower levels, so if you're sleeping on a futon on the floor or tatami mats, or using a highly breathable bed, your bedding can get cold easily. Naturally, using cold bedding will make your body cold, and your extremities like hands and feet can become completely chilled.
When your hands and feet are cold, blood vessels constrict, preventing efficient heat dissipation. This means your core body temperature won't drop, making it difficult to fall asleep.
3 incorrect cold weather remedies that degrade sleep quality
On cold nights, you might try various cold weather remedies to sleep, but perhaps those very remedies are degrading your sleep quality...
1: Wearing too many layers or multiple pairs of socks
Many people wear thick clothing to bed on cold days, but excessive layering can hinder heat dissipation, so it should be avoided. Also, wearing too many layers can restrict body movement, making it difficult to turn over smoothly, which can contribute to a decrease in sleep quality.
Similarly, wearing multiple pairs of socks should be avoided as it hinders heat dissipation from the feet, making it difficult to regulate core body temperature effectively. If you wear socks to prevent cold feet before sleeping, either take them off when you get into bed or choose loose-fitting socks that can come off easily during sleep.
2: Leaving electric blankets or foot warmers on all night
Electric blankets and foot warmers can improve sleep quality if used correctly, but avoid leaving them on all night. If left on all night, the inside of the futon can become excessively hot, hindering core body temperature dissipation and reducing sleep quality.
Electric blankets and the like should be used to warm the futon before sleeping. Turn them off when you go to sleep, or use a timer function to prevent them from staying on for too long.
3: Piling on multiple layers of bedding such as futons or blankets
Similar to wearing too many layers or multiple pairs of socks, excessively layering bedding is not recommended as it can hinder the regulation of core body temperature. Additionally, popular down comforters, known for being light and warm, have a tendency to retain moisture, so if not chosen carefully, they might actually decrease sleep quality.
For comfortable sleep, not just the duvet, but also the mattress and futon are important. Heat inside the futon can also escape from below, so choose a mattress or futon that can maintain a comfortable temperature and humidity inside, preventing cold from the bottom.
Also, the order in which you layer different duvets varies depending on the material, so be careful when combining various blankets. Natural fiber blankets, such as cotton blankets with moisture-absorbing properties, can be placed under the duvet to maintain appropriate humidity levels inside the bedding. Conversely, acrylic blankets can be placed on top of the duvet to enhance warmth.
4 ways to get a good night's sleep on cold winter nights
The "autonomic nervous system," which is deeply related to sleep, is divided into two types: the sympathetic nervous system, which is dominant when the body is active, and the parasympathetic nervous system, which is dominant when the body is resting. They balance each other to regulate the body. To get good quality sleep even on cold nights, it is important to activate the parasympathetic nervous system.
During the day, the sympathetic nervous system becomes active, increasing heart rate and blood pressure, and making the brain and body active, which improves concentration and athletic performance. Conversely, at night, the parasympathetic nervous system becomes active, decreasing heart rate and blood pressure, and putting the brain and body into a relaxed state. Therefore, activating the parasympathetic nervous system at bedtime is key to falling asleep smoothly.
1: Controlling core body temperature
Your body temperature isn't constant throughout the day; it fluctuates by about 1 degree. It's controlled by your internal clock to be higher during the day for activity and lower at night to allow your brain and organs to rest during sleep. There's a deep connection between these temperature changes and sleep.
When falling asleep or at the beginning of sleep, the body releases heat from the hands and feet to lower core body temperature, so if heat can be effectively dissipated from the skin of the hands and feet, it leads to smooth sleep onset. As sleep deepens, the body enters a resting state, causing core body temperature to further decrease, leading to higher quality sleep.
Taking a bath before sleep and drinking decaffeinated hot beverages are recommended.
Bathing in slightly lukewarm water
Taking a bath in slightly lukewarm water (around 40℃) about 1-2 hours before bedtime can not only enhance the parasympathetic nervous system through its relaxing effects but also induce sleepiness as your body temperature drops.
However, be aware that taking a hot bath over 42℃ immediately before bed is said to elevate the sympathetic nervous system.
Caffeine-free hot drinks
While experiments have reported that cold drinks can induce sleepiness, many people find that drinking a warm beverage helps their body relax and activates the parasympathetic nervous system, making it easier to fall asleep. In such cases, it's a good idea to drink a warm beverage one to several hours before bedtime.
Recommended options include plain hot water, hot milk, ginger tea, and other caffeine-free beverages. Herbal teas like German chamomile, which have long been favored in Western countries for promoting restful sleep, are also good choices.
While alcohol might temporarily make it easier to fall asleep, it can degrade sleep quality, so it's generally safer to avoid it.
2: Warming the room
In a cold room, your body can't dissipate heat effectively, making it difficult to fall asleep. Warming your room to around 20-22℃ before bedtime can help you fall asleep smoothly. However, using air conditioning all night can make the room excessively hot or dry, so turn it off before sleeping or use a timer function to avoid sleeping in an air-conditioned room for long periods.
Also, a smaller temperature difference between inside and outside the futon leads to a more comfortable awakening, so the room temperature at wake-up time is important. Mornings are also the coldest time of day, so if you struggle to get out of bed on cold mornings, set your air conditioner to turn on about an hour before your wake-up time, aiming for a room temperature of around 20-22℃. This can help prevent cold hands and feet even in cold weather.
If your room temperature drops quickly, try installing insulating film on windows to block cold air, setting up insulating boards, or switching to thicker curtains.
3: Warming the bedding
Similar to room temperature, cold bedding can draw heat from your hands and feet, preventing proper heat dissipation and making it difficult to fall asleep. The ideal bed temperature (temperature inside the futon) is said to be 32-34℃, so it's recommended to warm your bedding before sleep using a futon dryer, hot water bottle, electric blanket, or electric foot warmer. Warming it about 20-30 minutes beforehand can help you feel less cold and fall asleep smoothly.
Using an electric blanket or foot warmer all night can make the futon excessively hot, so these should only be used as a temporary measure to aid in falling asleep. After that, use bedding suitable for maintaining warmth.
4: Switching to winter bedding materials
To maintain the ideal bed temperature of 32-34℃ during sleep, it's crucial to choose bedding materials appropriate for the season. In autumn and winter, when temperatures drop, switch to winter bedding materials that offer high insulation and warmth.
Turning over in bed helps regulate the temperature inside the bedding and body temperature, so be careful about using heavy blankets that make it difficult to turn over. Piling on too much bedding just because it's cold can potentially decrease sleep quality.
Down comforters are popular winter bedding because they are warm and light, but they don't release moisture easily, so careful selection is necessary. The humidity inside the futon is ideally around 45-55%, so consider the combination of not just the duvet, but also the mattress and futon to improve sleep quality.
Furthermore, it's important to choose pajamas that can control core body temperature during sleep, not just bedding. Warmth is important, but highly moisture-absorbent materials that can absorb sweat during sleep are also recommended. Recently, there's a wide variety of recovery wear that helps care for body fatigue during sleep, so those looking to further improve their sleep quality should check them out.
Benefits of getting a good night's sleep in winter
Winter is a season where physical and mental performance can easily decline due to poor blood circulation, but improving sleep quality can enhance daytime performance. Furthermore, sleep quality affects not only athletic ability but also concentration, directly impacting work performance.
Cold days make you tired easily.
On cold days, your body unconsciously tenses up to prevent heat from escaping. As a result, muscles stiffen, blood flow deteriorates, and performance decreases. Additionally, on days with low outdoor temperatures, your body uses muscles to maintain its temperature, so fatigue accumulates easily even without special exercise.
In other words, winter is a season where muscles stiffen, blood flow worsens, and you tend to get tired more easily, leading to a decline in athletic performance.
The relationship between good sleep and performance
There's a close relationship between lack of sleep and daytime performance; it's said that "two weeks of 6-hour sleep is equivalent to the brain performance of an all-nighter."
However, it's difficult to ensure long hours of sleep every day. But if the quality of sleep is high, you can efficiently rest your body and brain within a limited sleep time, maintaining a clear head the next morning. Benefits such as improved concentration and a stable, less irritable mental state can be expected, which contribute to work performance.
In other words, improving sleep quality through proper measures even in the cold winter leads to better work results.
How to get a good night's sleep on cold nights
Good quality sleep is very important for both physical and mental health. On cold days, it can be hard to fall asleep, so take the right measures to aim for a good night's sleep.
