Temperature and sleep

Throughout human evolution, temperature has been a strong cue for sleep and wake time. It serves as a so-called “zeitgeber” or time-giver, which is an external cue influencing our circadian rhythm. When researchers looked at sleep in three geographically distinct pre-industrial societies, they found that subjects fell asleep just as the external temperature began to drop and continued as temperatures declined. Similarly, waking up often occurred before sunrise when the ambient temperature was at its lowest and corresponded with the narrowing of blood vessels, or vasoconstriction, as indicated by the temperature of the fingers.

Thermoregulation and temperature also impact the different stages of sleep. It’s been found that about two hours prior to sleep onset, your core body temperature begins to drop and reaches its lowest point during slow-wave sleep. Additionally, the temperature in the brain also slightly decreases at this time.

Our core body temperature hovers around 98.6 °F (37 °C) but fluctuates by about two degrees Fahrenheit during the night.

Decrease in one’s core body temperature during sleep comes from reducing our metabolic output, decreased muscle tone, and decreased sympathetic tone from vasodilation leading to heat loss distally.Valerie Cacho, MD, Integrative Sleep Physician, and Women’s sleep expert

Dr. Cacho added that while melatonin is most often associated with light exposure, a cool room and the drop in body temperature can also help to increase the production of this “sleep hormone.”