Dr. Kelvas notes that when the room is too hot or cold, the body has difficulty regulating these hormones, which can lead to difficulty falling asleep or staying asleep.

The common recommendation for ambient room temperature is in the range of 60 °F (15.5 °C) to 68 °F (20 °C),�according to the Sleep Foundation. It’s been found to aid the body’s thermoregulatory process to promote healthy sleep latency (the time it takes to fall asleep) and good quality sleep overall.

Temperature and the body

The human body has its thermoregulatory mechanism�that allows us to maintain a healthy internal body temperature regardless of the ambient temperature of our environment. In addition, the body uses a complex interplay of physiological responses to regulate body temperature, including sweating, shivering, and changes in blood flow to the skin.

Sweating is one of the body’s primary mechanisms for cooling down. When the body’s internal temperature rises, sweat glands produce moisture that evaporates from the skin’s surface, releasing heat and hence cooling the body.

Conversely, shivering is the body’s mechanism for generating heat when the internal temperature drops. Shivering is a reflexive response that causes muscles to contract rapidly, generating heat to raise the body’s temperature.

Vasodilation, dilation, and constriction of blood vessels can also impact body temperature. For example, blood vessels near the skin’s surface dilate when the body needs to cool down, allowing more blood to flow through them. This increase in blood flow helps to release heat from the body. On the other hand, when the body needs to conserve heat, blood vessels near the skin’s surface constrict, reducing blood flow and conserving heat.

All of these mechanisms play a role as you get ready for bed and ease into the different stages of sleep. You may have experienced this shift in temperature before. For example, whenever you feel cold in bed and putting socks on makes you feel a bit warmer, that’s because a lot of heat loss occurs through our extremities — hands and feet. Thus, covering them will help make you feel warmer. Conversely, when you feel warm under the covers but don’t want to fully kick off the blanket, sticking your feet out from under the blanket may be the heat relief you need to be able to fall asleep.

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.”

If the external temperature is too warm, studies have found it to have a negative impact on both the rapid eye movement (REM) phase of sleep and slow-wave sleep (SWS). Dreams occur in the REM sleep phase, when your brain is highly active. On the other hand, SWS is associated with less brain activity but increased physiological recoveries, such as the release of human growth hormone, muscle recovery, and the flushing of toxic material, including beta-amyloid plaques, from the brain. However, both are very important for optimal physical and cognitive well-being.