The Sleep and Temperature Connection

If you’re like us, there are a lot of things that will keep you up at night. Whether it’s tomorrow’s to-do list that won’t leave your mind or that pesky beam of light that you just can’t quite get your black out curtains to block out, achieving deep, restful sleep can oftentimes be an uphill battle.

Among the many variables determining your sleep success, temperature is a particularly interesting one because the ambient temperature of your room might have more to do with your ability to drift off to sleep than you might think. And the ambient room temperature the sleep experts suggest is surprisingly low.

Before we get into all the details of why temperature is so critical for sleep, it’s important to understand that the ability to fall asleep, stay asleep, and get enough sleep to feel rested and be productive for the following day is dependent on a complex set of interactions between your brain, nerves, hormones, and core body temperature.

Your core body temperature correlates with the quality of both REM (rapid eye movement) and slow-wave sleep you get. 

What is the ideal room temperature for sleep?  

The temperature of the room you sleep in and the temperature of your body while you are sleeping or falling asleep are some of the most important factors affecting your sleep. Here’s why the effects of either exposure to warmer or cooler temperatures can rouse you from REM sleep and slow-wave sleep. These two phases are fundamental to the quality of your sleep.

Let’s explore why a cooler core body temperature is more conducive to deeper sleep.

You might think warmer temperatures would be more conducive to drifting off to sleep from experience driving at night in a car with the heater on and that a cooler room might make you feel more alert. But research shows that a slightly cooler bedroom temperature helps us to fall asleep and pass into deep sleep more quickly.

Experts say the best temperature to fall asleep and stay asleep is between 60 and 67 degrees Fahrenheit. 

Setting the bedroom thermostat temperature correctly is one of the most important factors that regulate your sleeping process along with light, noise, and the ability to relax both mentally and physically as nighttime approaches.

Your core body temperature decreases as you get closer to falling asleep and continues to decrease while in the middle and later stages of sleep. Your skin temperature remains higher than the core temperature throughout sleep. Your body controls arousal from sleep and temperature regulation in the part of the brain called the hypothalamus.[1,2] 

The ability to change your temperature while asleep is dependent on what stage of sleep you’re in. For example, you might nestle deeper into the covers or throw them off without even realizing it in the interest of keeping your body temperature consistent.

Core body temperature and skin temperature affect your sleep 

Lowered body temperature is the cumulative result of decreased physical and mental activities, relaxed muscle tone, and changes in your nervous system that contribute to the sleep-related fall in core body temperature (CBT). 

For a clearer picture of how your body goes about cooling down, think about how you experience your body cools itself when you exercise. When you start exercising your CBT increases. When your nerves identify the upward shift in body temperature your body responds by sweating to cool down. 

Sweating is the result of your brain sending signals to your blood vessels in your skin causing them to dilate. It allows more blood and heat to be dissipated through the skin and as the sweat dries, your body feels cooler.

Similarly when you fall asleep, your CBT decreases further while skin temperatures remain higher.[8] The importance of maintaining skin temperature at just the right temperature for sleep maintenance (not too warm, not too cool) has been suggested as a strategy for improving sleep.[7] The range of normal skin temperatures are 90-98ºF.

One study investigated skin temperature manipulation by using a “thermosuit” to increase the skin temperature by 0.4ºC while not changing the core body temperature. The results indicated decreased wakefulness and a shift to deeper levels of sleep in both young and elderly people. The subjects in the study experienced two improved results: 

  • They received double the amount of slow-wave sleep, and 
  • Fewer early morning awakenings.

Your circadian clock works to regulate your CBT. The CBT and propensity to sleep appear to vary inversely under normal environmental temperatures. For example, as the temperature of the body decreases, the desire to sleep increases and as the temperature of the body increases, the desire for sleep decreases and this is the case prior to awakening — at which point the body warms up. It is unknown whether this is a cause and effect phenomenon or coincidental.

Since there appear to be thermal sensory cells in the brain, it is believed that the sleep-wake cycle is triggered (either directly or indirectly) by heat or cold signals that help initiate sleep. One study showed that the process of sleep initiation also acts to keep people asleep by positive feedback mechanisms.[3] This positive feedback loop in the brain reinforces that once asleep, the brain tries to keep the body asleep.

Clothing, bedding, and ambient temperature

Ambient room temperature aside, what happens when you hop into your (hopefully) super-cosy bed, with its duvet covers abound and your sleep clothing of choice? 

Clothing and bedding are two other important factors in temperature regulation and sleep stages. Both excess heat or excess cold increase wakefulness and decrease slow-wave and REM sleep. It is believed that cold exposure from inadequate bedding impacts sleep stages more significantly than heat exposure.[6] If you are constantly curling up or shivering, falling asleep and staying asleep are impossible.

But, when cold can be reduced to a comfortable level, heat appears to affect sleep quality more significantly, especially if no adjustments in temperature can be made such as with fans or air conditioners. Just throwing off blankets or sleeping with fewer clothes cannot always keep you cool enough for comfortable sleep.

In a recent sleep study on children researchers found that under cooler conditions, warming of the feet using bed socks had positive effects on sleep by:

  • Shorter sleep onset, 
  • Longer sleep time, and 
  • fewer awakenings during sleep. 

CBT did not change with these findings. The authors concluded that increasing the temperature of cold feet could improve sleep quality.[5] 

Is it better to be warmer or cooler during sleep? 

It’s easier to warm up with blankets but not always easy to cool down by removing them. This overheating often results in increased wakefulness and decreased slow-wave sleep and REM.[11] 

Heat-related effects on sleep usually appear earlier in the sleep period, regardless of stage, rather than during the later period of sleep before awakening. 

One difference between cold and heat exposure during sleep is that cooler temperatures mainly affect the later segment of sleep, where REM is predominant.

Summer, climate change and sleep

Recent studies are starting to point to warm temperatures at night generally affecting the quality of our sleep. Depending on if you have air conditioning or not, exposure to heat throughout the day could ultimately affect your ability to cool down enough to go to sleep at night. 

Your body’s compensatory mechanisms might be overcome by the daytime heat making it difficult for your CBT to cool down to an ideal temperature at night. This can make it much more difficult to fall into a good night’s sleep.

Numerous physiological studies have shown that the thermal environment is an extremely important determinant of sleep quality. A recent survey of 765,000 US residents found that higher temperatures are linked to lower sleep quality.[13]

A Japanese study found that hot summer nights led to poor sleep at a population level. And this recent publication on the effects of climate change on sleep might have you looking more closely into how to control your room temperature at night to keep control over your sleep quality. Similar findings were mirrored in this recent meta-analysis summarized the research regarding climate change and sleep.[14]

What to do 

The best thing to do is to start by examining the temperature of your bedroom. You can do that with a digital room thermometer that costs less than $10. Then try keeping your bedroom between 60-67º throughout the night. You can use lighter blankets and sheets in the summer and layer blankets in fall and spring so as not to overheat.

Taking a shower or a bath before bed is a good way to help your body start the process of cooling down before sleep. Also, consider meditation before bed. Meditation is a great way to slow your body down allowing your muscles and mind to rest, which will help to lower your core body temperature.

Most importantly, getting your sleep temperature right can take time and experimentation. Make sure you track your sleep either with a sleep tracker or sleep journal. Check out the Remrise app for tracking your sleep quality.

References

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