Old wives’ tales claim that people sleep better in colder temperatures, with an open window letting in the cool night air. In this case, it appears that numerous grandmothers were correct. New research has found that there is a link between colder temperatures in a room and a higher quality of sleep.
Temperature and the Circadian Rhythm
The circadian rhythm, or our body’s internal 24-hour clock, dictates more than just sleep and waking. This internal rhythm also affects our body’s core temperature. In a healthy person, body temperature begins to rise after waking in the morning and is highest at midday. Body temperature dips slightly in the mid-afternoon, when many people feel sleepy, and then sharply just before bedtime. As we fall asleep, veins and other blood vessels near the surface of the skin dilate and release heat, lowering peripheral skin temperature. Body temperature then stays lowest throughout the night while we sleep.
There is a clear connection between body temperature and sleepiness, but the physiological basis of this connection is unknown. In fact, this correlation is the subject of several studies currently being conducted in the field of circadian biology.
Thermoregulation and Sleep
While a cool room appears to improve sleep, human body temperature is usually not controlled by our environment. Thermoregulation is a complex biological process that is controlled by the hypothalamus of the brain. The preoptic nucleus of the hypothalamus senses and responds to the temperature of blood. When blood temperature sinks too low, the hypothalamus tells the body to shiver and generate heat. When blood temperature becomes too high, humans sweat and vasodilate to release heat.
These reactions are innate and occur without our conscious control. However, there also is a behavioral component to thermoregulation. When people feel cold or hot and they cover themselves or remove a layer.
How Does External Temperature Affect Sleep?
Although human thermoregulatory systems are facile at maintaining an ideal body temperature in many situations, the system partially closes down in REM sleep. The shivering and sweating reflexes controlled by the hypothalamus are not as responsive or as effective. Without fully functioning innate responses, thermoregulation requires a behavioral response. People may toss and turn, kick off a blanket, or they otherwise attempt to warm or cool themselves. The resulting activity can disrupt sleep or even wake a person up.
Because the ideal body temperature while asleep is very low, most people will not need as much thermoregulation and thus not toss or turn as much when they are in a cool room. This may lead to deeper sleep, as REM sleep will not be interrupted by movement.
Can Body Temperature Affect Insomnia?
Because of research in chronobiology showing a link between low body temperature and better quality sleep, it is not surprising to find that abnormalities in this temperature cycle have been linked to insomnia. Sleep onset insomnia, or difficulty falling asleep, has been linked to a delay in vasodilation and subsequent lowering of peripheral skin temperature. People who have sleep maintenance insomnia, or difficulty staying asleep, have an elevated temperature at night. Many researchers believe that insomnia and elevated body temperature may both be caused by hyperarousal in the hypothalamus.
There is still much that remains unknown about the human circadian rhythm and its effect on physiological processes. This area is being actively studied as the resulting knowledge will have meaningful effects on health and quality of life. However, it is safe to say that sleeping in a cool room will often lead to a better night’s sleep.