A brief discussion on the impact of temperature on sleep quality: Ambient temperature

"Spring makes you sleepy, autumn makes you tired, summer makes you nap, and winter makes you sleepy in March." This shows the great impact of environmental temperature (climate) on sleep. In summer, the weather is hot and you can't rest well at night, which makes you sleepy during the day; in winter, the weather is cold and the oxygen is thin, which can easily cause you to feel sleepy and dizzy.

If you are suffering from difficulty falling asleep at night, frequent awakenings, daytime sleepiness, and irritability, the possible culprit is the sleeping environment (such as temperature, humidity, noise, light, etc.). The ambient temperature includes the bedroom temperature, bedding temperature, etc. What range of bedroom temperature is most suitable for sleep?

The National Sleep Foundation (NSF) of the United States recommends that the optimal bedroom temperature for sleep should be between 15.5°C and 19.4°C. Literature research shows that the quality of insomnia is highest in an environment of 26°C, followed by 23°C, and the worst is 30°C[1].

"The Secrets of Sleep and Regulation Techniques" recommends: The bedroom environment should be between 20℃ and 23℃.

According to research, people are most likely to fall asleep when the temperature of the blanket is between 32 and 34 degrees Celsius. If the blanket is too cold, it will take a long time to warm up with body temperature, which will not only consume the body's heat energy, but also make the cerebral cortex excited after a period of cold stimulation, thus prolonging the time to fall asleep or causing shallow sleep.

Based on the changes in electroencephalogram (EEG), electrooculogram and mandibular electromyography during sleep, sleep is divided into non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. NREM sleep is further divided into three stages, N1 to N3 [2]. Stage N3 is also called deep sleep, accounting for about 20%. During the entire sleep period, REM and NREM alternate, with a cycle of about 90 minutes.

01

Effects of high and low temperature environments on sleep quality

The total thermal resistance of bedding is defined as the total heat transfer resistance from human skin to the room environment when lying flat, including the thermal conductivity resistance of pajamas, quilts and mattresses, the thermal resistance of the air layer between the body and the quilt and bed, and the heat exchange resistance of the outer surface of the bedding [3].

When the total thermal resistance of bedding is small, a low-temperature environment will interfere more strongly with sleep than a high-temperature environment, which is manifested as increased wakefulness and N1 duration, shortened NREM and REM sleep duration, and decreased sleep quality[4].

It can be seen that when sleeping in summer, do not set the air conditioner temperature too low (generally not less than 24℃); when sleeping in winter, do not set the air conditioner too high (generally >27℃) or place the heater at the head of the bed.

Sun Simiao said in his "Prescriptions for Emergencies": "...Do not place a stove near the head. It will attract fire over time, causing a heavy head, red eyes, and dry nose..."

In experiments on rats, a moderate increase in ambient temperature, such as from 22°C to 24°C to 29°C to 30°C, can increase the amount of NREM and REM sleep and reduce wakefulness time.

On the contrary, when the ambient temperature drops from 22℃ to 24℃ to 18℃, the amount of sleep decreases, especially the decrease in REM sleep. In cats, compared with an ambient temperature of 23℃, REM sleep increases at 30℃, but both NREM and REM sleep decrease at 35℃, 15℃, and 7℃.

The effect of low temperature on human sleep is similar to that of animals. For example, at 13℃, compared with a more normal 25℃ environment, human NREM sleep, especially REM sleep, is significantly reduced, and wakefulness time is increased. At moderate ambient temperatures, such as from 19℃, 22℃, 25℃, 29℃ to 34℃, humans do not show an increase in NREM and REM sleep similar to animals.

In 11-week-old infants, when the temperature increased from 24°C to 28°C, the infants showed a decrease in the transition from REM sleep to wakefulness, suggesting that moderate ambient temperature may improve sleep[5]. Studies have shown that in cold winter, warm bedding can help the elderly fall asleep faster and improve sleep efficiency by 5%, especially reducing blood pressure when the elderly wake up early[6].

02

Effects of dynamic thermal environment on sleep quality

By testing the effects of U-shaped (first decreasing and then increasing) or inverted U-shaped (first increasing and then decreasing) changes in ambient temperature throughout the night on human sleep quality, it was found that it is more difficult for the human body to fall asleep in a relatively cool environment during the sleep phase (within the comfort zone), while in the later stages of sleep (within the comfort zone), the gradually increasing temperature can help the human body prepare for waking up and improve work efficiency the next day[7,8].

Moreover, the gradually decreasing ambient temperature after falling asleep can delay the time when the lowest body temperature occurs, and appropriately increase the duration of deep sleep[9]. Studies have shown that a U-shaped change in the ambient temperature during sleep is more conducive to improving human sleep quality and work efficiency[10].

In summary, ambient temperature has a significant impact on sleep quality. Too high or too low a temperature is not conducive to sleep. By setting a reasonable temperature range and a dynamic thermal environment, you can reduce the duration of wakefulness, increase the duration of deep sleep and the total amount of sleep.

[1] Lan L, Pan L, Lian Z, Huang H, Lin Y, et al. Experimental study on thermal comfort of sleeping people at different air temperatures. Build and Environment, 2014, 73: 24–31.

[2] IBERC, ANCOLIISRAELS,CHESSON A, et al. The AASM manual for the scoring of sleep and associated events: rules, terminology and technical specification[M]. Westchester: American Academy of Sleep Medicine, 2007.

[3] PAND, LINZ, DENGS. A mathematical model for predicting the total insulation value of a bedding system[J]. Building and Environment, 2010, 45(8): 1866-1872.

[4] HASKELLEH,PALCAJW,WALKERJM, et al. The effects of high and lowambient temperatures on human sleep stages[J]. Electroencephalography & Clinical Neurophysiology, 1981, 51(5):494-501.

[5] Tang Xiangdong. The impact of environmental factors on sleep. Guangdong Medical Journal. 2007:28(1):6-8.

[6] Xia LL, Lan L, Tang J Y. Effects of two heating methods on sleep quality in the elderly. In: Proceedings of the 11th International Symposium on Heating, Ventilation and Air Conditioning (ISHVAC 2019). Harbin, China, July 12–15, 2019.

[7] Lan L, Lian ZW, Lin Y B. Comfortably cool bedroom environment during the initial phase of the sleeping period delays the onset of sleep in summer. Build Environ, 2016, 103: 36–43.

[8] Lan L, Lian ZW, Qian XL, et al. The effects of programmed air temperature changes on sleep quality and energy saving in bedroom. Energy Build, 2016, 129: 207–214.

[9] Togo F, Aizawa S, Arai J, et al. Influence on human sleep patterns of lowering and delaying the minimum core body temperature by slow changes in the thermal environment. Sleep, 1999, 30: 797–802.

[10] Lan Li, Lian Zhiwei. Improving the thermal environment during sleep can improve sleep quality. Chinese Science Bulletin. 2020, 65(7): 533-534.

Reprinted from "China Sleep Research Society"