In case 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.
Looking at 10 elderly men’s responses to higher bedroom temperatures and their sleep quality, researchers found that even mild heat exposure during the nighttime sleep period would increase the thermal load, decrease REM, and increase wakefulness and whole-body sweat loss.
In addition, research at the University of California, Los Angeles found that warm-blooded animals with higher body temperatures have lower amounts of REM sleep, while those with lower body temperatures have more REM sleep.
Humidity also contributes to sleep quality. One study reported that humid heat exposure increased wakefulness and decreased REM sleep and SWS. Humidity also suppressed the decrease in core body temperature.
On the contrary, when your room is too cold, Dr. Kelvas claimed that the body may need to expend energy to stay warm, which can keep it from entering a deeper sleep.
Benefits of sleeping in a cold room
It might seem subtle that room temperature would profoundly impact sleep, but many people who have lived through a heat wave during summer can relate. For example, have you ever had to sleep with a cold towel on top of you or downstairs in the living room where there was more air if you didn’t have air conditioning? Or have you ever woken up groggy after getting night sweats? As women transition through menopause, hormonal changes make them even more sensitive to external temperatures. Additionally, even the body temperature of a cycling woman changes slightly throughout the month. More precisely, it’s been seen to increase during ovulation.
An optimal bedroom temperature, however, goes further than simply helping you wake up more refreshed. Here are four benefits of a cool room that will make you want to dial down your thermostat tonight.
Better sleep quality
Sleeping in a cold room allows your body to release adequate amounts of melatonin and prevents cortisol (stress hormone) from rising and waking you up. Studies have shown that when you create the environment for the body to drop its core temperature throughout the night, you’ll spend more time in two of the most important restorative sleep phases: REM and slow-wave deep sleep. Additionally, you won’t have to worry about night sweats waking you up and causing sleep disturbances at night.
Fall asleep faster
Your core body temperature must drop so you can fall asleep. You will fall asleep faster when you create an environment for your body to release excess heat and support its natural circadian rhythm. A good rule of thumb to follow is if your sleep latency is between 10–20 minutes, it’s considered healthy. Insomniacs, for example, tend to experience difficulty sleeping because their bodies have a higher core temperature, which causes them to stay awake while their bodies try to cool down. This can interrupt or delay their sleep.
Better weight management
Cold temperatures activate the body’s “brown fat,” which is a very metabolically active tissue, also known as good fat. The more brown fat you have, the more white fat (the fat around your tummy) will burn. Researchers in Australia put men through a controlled sleep environment with different room temperatures. They found that following a month of sleeping in a cooler environment at 66 °F (18.8 °C), the volume of beneficial brown fat in the body had nearly doubled.
Lower risk of diseases
Because of the increase of brown fat, insulin sensitivity increases, which can be key to preventing type 2 diabetes and other metabolic conditions. The Australian study also found that during the time participants slept in the 66 °F (18.8 °C) room, they burned more calories during the day.
Furthermore, sleeping in a cool room may help to prevent Alzheimer’s disease by helping the body to tap into all the restorative stages of sleep along with acquiring the recommended seven to nine hours of slumber. A cross-sectional study published in the JAMA Neurology found that both short and long sleep durations were associated with worse outcomes for older adults, such as “greater beta-amyloid plaque burden, greater depressive symptoms, higher body mass index, and cognitive decline, emphasizing the importance of maintaining adequate sleep.”
