I was always sleep deprived. For many years, I struggled to get decent sleep. Beside me, my wife slept like a rock, night after night. I would go to bed before her and get up after her, and yet, I was still tired. The poor quality of my sleep affected my mood, productivity, and desire to exercise, and I found that I often ate more than I needed trying to boost my energy.
What was my problem? I knew that I would often wake up hot, and it would take forever to cool down and get back to sleep, but I had no clue what was really going on at night. As an engineer with 20 years of working in temperature physics, I did what you would expect: I equipped my bed with temperature sensors and logged many nights of thermal data. What I discovered surprised me. I found that the mattress beneath me became hotter and hotter until it nearly reached my core temperature, and I would become overheated, causing me to roll over, looking for a cool spot. This cycle happened every 30 to 45 minutes throughout the night, completely fragmenting my sleep. Once the bed was hot everywhere, I would have to remove the blanket, get up, open a window, and walk around until I had cooled down enough to finally get back to sleep, and an hour later, I’d wake up cold because of the open window and lack of blankets. It was torture!
What I discovered is what many people already know—the temperature of your sleep environment and the regulation of the heat your body produces during the night are critical to getting good quality sleep. Sleep temperature is one of the most overlooked factors in sleep quality.
Thermodynamics and bedding down for the night
Think about your bedding. Why do you use blankets and a thick insulating mattress? Why do people sleep better in a cool room? Your nightly experience—whether you recognize it or not—is crafted around temperature regulation. Good quality sleep requires an environment that is disturbance free so you can sleep without interrupting your sleep cycle. This includes avoiding sleep disturbances caused by temperature, which are more influential than many people realize.
A human body generates approximately 80 watts of heat while sleeping, which is about the same as a standard light bulb. This doesn’t seem like much, but consider the old Easy Bake Oven, a kid’s toy that bakes cookies with a light bulb. A little heat source enclosed in insulation can get very hot. While sleeping, your body is like that light bulb and must disperse heat to stay comfortably cool. If you get too hot, you are forced to either change your environment (open a window, roll over) or change the amount of insulation around your body (kick off the blankets, stick a leg out) otherwise, your body will try to keep cool by sweating and circulating more heat through the blood to your arms and legs. This all results in fragmented sleep, preventing you from having an undisturbed sleep cycle.
Being too cold is just as disruptive as being too hot. If you get too cold, your body limits circulation to your arms and legs to preserve its core temperature, making your extremities cold. Sleeping in a tense, shivering ball fighting to warm your hands and feet also fragments your sleep, so you must add blankets to keep warm.
The ideal sleep environment enables your body to be at a uniform constant temperature so that you subconsciously expend less energy managing your temperature. This means no sweating or shivering, and your hands and feet are at a comfortable temperature without your body working hard to maintain your temperature. Sleep is designed to regenerate your brain, allow you to subconsciously organize your thoughts, and bring rest to your body. If you are not struggling to regulate your temperature throughout the night, your body and brain will get the rest they need.
The role of temperature in sleeping and waking
Throughout the day, your body temperature naturally varies, and in the evening, your core temperature drops to tell your body to prepare for sleep. It can take three to four hours for your body temperature to drop approximately 0.9 F, and during this temperature drop is when you fall asleep easiest. Your body does a wonderful job cooling your core to prepare you for sleep. In a natural environment, cooling down for sleep is synchronized with the cooling of the day into night, however, our modern environment can mess this up. It doesn’t take much!
If anything disturbs your body’s drop in temperature, it becomes harder for you to fall asleep and stay asleep. If you exercise vigorously an hour before bedtime, your body heats up, and you won’t sleep until you cool down. If you eat a large hearty meal in the evening, your digestive system works overtime, heats you up, and makes it difficult to fall asleep. Many other factors, including menopause, obesity, and metabolic issues, can prevent the body from cooling properly, thus diminishing the quality of sleep. It can and should take you some time to fall asleep but being too hot at bedtime can extend your sleep onset time significantly, depriving you of much-needed sleep.
Conversely, in the morning, your body naturally rouses you by raising your core temperature, which matches the natural rise in temperature from morning daylight. Having a premature temperature increase of your sleep environment will cause you to wake up earlier than desired, again shortening your sleep cycle. This is very common for older people, and studies have shown that a small change in skin temperature can cause premature morning rousing.
Will better management of your body temperature improve your sleep?
The short answer is yes. Some people will experience greater rewards from better thermal management of their sleep environment than others, but all will experience some benefit. Those who often wake up sweating or suffer from menopausal hot flashes will benefit greatly by being cool while sleeping.
What can be done to better manage the thermodynamics of your sleep?
There are some simple steps that can help with this such as:
- Don’t engage in activities that make you hot before turning in, such as exercising too close to bedtime, overeating before bed, or sitting on a hot couch under a pile of blankets before calling it a night.
- Do cool down before bed by lowering the thermostat in your bedroom or taking a cool shower.
- Choose bedding that breathes and doesn’t overheat you at night
For some people, these measures are not enough. A more sophisticated solution may be required, such as a bed-cooling product, which actively manages your body temperature during the night and greatly reduces the amount of temperature-induced sleep disturbance you might experience. If you suffer from poor sleep, it may be due to temperature, and trying a product-based sleep solution may be a step towards better sleep.
