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Body Thermoregulation and Sleep


You may have noticed that during hot, summer days it seems impossible to fall asleep without the AC. And maybe sometimes when it is late at night and past your bedtime, apart from feeling tired, you also feel cold.

How are these things connected to your sleep? Throughout the day and night, your brain regulates temperature by making your body slightly warmer or cooler. Ambient temperature can have an effect on your body temperature – this is why you shiver or sweat – your body is trying to prevent you from losing or gaining too much heat.

Here we talk about temperature changes in the body and how to act in respect to those changes in order to ensure good quality sleep.

What is thermoregulation?

It is the action our body performs 24/7 in order to maintain the optimal temperature. That temperature equals 97.7–99.5 °F in healthy humans. This refers to the core body temperature, meaning this is the ideal temperature for the functioning of our internal organs and tissues – heart, liver, blood. For example, the temperature in our extremities may vary greatly – our hands can be freezing cold if we’ve just built a snowman without gloves or extremely hot if we are touching scorching sand. However, our core body temperature remains more or less the same.

It is well protected by muscles, tissues, fat, and skin, which make our shell temperature – and shell organs are exposed to external influences to a great extent. They are also a vessel through which internal organs are cooled down or warmed up.

During one day, the temperature slightly changes many times. From the time we wake up in the morning, our body temperature keeps rising – it’s the highest when we feel the most alert. Temperature drops usually about mid-afternoon (it’s when you feel sleepy after lunch), after which it rises again. Your body temperature falls down as your bedtime approaches.

After you fall asleep, the body temperature changes depending on the sleep stages. In the REM (rapid eye movement) stage, there is the least effort of your body to regulate temperature. About 5 am most people reach the lowest point in body heat, which keeps growing until we wake up.

Hypothalamus is the area of the brain which regulates temperature (it’s the same part which is highly involved in how we fall asleep). It receives the information about the body temperature and sends out the necessary orders for regaining homeostasis (balance). It will tell your sweat glands to work more if the body is too hot or order muscles to shiver in order to produce warmth.

However, our temperature can be regulated by external factors, like AC, clothes, shower and other.

Thermoregulation and body rhythm

Our temperature is a part of a complex system in our body which regulates many processes. The mentioned fluctuation also happens with our energy levels, and neurotransmitter and hormone release – however, the highs and lows are different for every person – just like the preferred sleep-wake time. They are a part of your internal biological clock called the circadian rhythm.

Your circadian rhythm may be such that your temperature (and alertness) is the highest in the morning, and this means your chronotype is that of a morning person. If you are an evening type, you might have your peak at about 7 pm.

Thermoregulation and body rhythm

Our temperature is a part of a complex system in our body which regulates many processes. The mentioned fluctuation also happens with our energy levels, and neurotransmitter and hormone release – however, the highs and lows are different for every person – just like the preferred sleep-wake time. They are a part of your internal biological clock called the circadian rhythm.

Your circadian rhythm may be such that your temperature (and alertness) is the highest in the morning, and this means your chronotype is that of a morning person. If you are an evening type, you might have your peak at about 7 pm.

Thermoregulation during sleep – what is the ideal room temperature?

During sleep, human core body temperature drops by a couple of degrees. Our metabolism slows down. This might be because of energy saving so that our body can direct energy to where it is needed them most. The human brain and vital organs use energy while sleeping, while the tissues are repaired and memory is consolidated, among other things.

A French study published in Presse Medicale stated that total sleep time is the highest in the thermoneutral zone and low when the temperatures are either warmer or colder. Thermoneutrality is described like this: about 87.8°F if you sleep without any pajamas and blankets and about 64.4°F if you sleep with pajamas and at least one sheet. These are the temperatures which are proven optimal for sleep duration and quality.

Not only does inadequate temperature wake us up, but it significantly reduces our REM sleep (also known as desynchronized sleep or paradoxical sleep), according to another study. It also somewhat negatively affects our deep sleep, but not as much as REM. This may be due to the fact that our body temperature regulation almost stops during REM sleep, leaving the body quite unprotected from external temperature changes. If the temperature is unfavorable, the body will simply not risk getting us into this stage of sleep, as it may be dangerous.

However, according to this study, if you get warmed up before sleep, like having a warm shower, you can increase your deep sleep and overall sleep continuity. It also promotes falling asleep as your body cools down after a shower, which naturally causes sleepiness.

Higher core temperature tends to wake us up, and a link was found between body temperature and insomnia. For example, those who have problems falling asleep also experience a problem with a delayed temperature rhythm (which probably equals delayed circadian rhythm). Another example is with insomnia patients who have problems maintaining sleep (they wake up and can’t fall asleep again) – their temperature is high at night. However, it seems that insomnia is not related to the inability of the body ‘thermostat’ to do its job, and the cause is likely to be something else. Future research might offer a solution to this matter.

What are the factors that can have an effect on thermoregulation at night or during sleep?

Our body can’t maintain the ideal core temperature at all times. There are some things which can lower or increase it.

Temperature increasing factors:

  • Illnesses like common cold (fever)
  • Exercising just before bed
  • Stress and anxiety
  • Temperatures above thermoneutral (above 64.4°F)
  • Hormonal changes (puberty, pregnancy, menopause)

Temperature decreasing factors:

  • Alcohol or drug abuse
  • Illnesses like anorexia and diabetes
  • Sleep deprivation
  • Temperatures below thermoneutral (below 64.4°F)
  • Hormonal changes (menopause)

There are some health problems and diseases which can affect thermoregulation as well. They will be described in the following chapter.

Thermoregulation and medical conditions

Here are some of the most frequent medical conditions which can have an impact on the body temperature.

Hyperthyroidism, hypothyroidism, and sleep

Both hyper- and hypothyroidism are problems with thyroid gland activity. Hyperthyroidism or overactive thyroid gland is the excessive production of thyroid hormone which regulates body temperature and metabolism. This leads to an increased appetite followed by weight loss, faster metabolism, and increased heat sensitivity and heart rate.

Hypothyroidism or underactive thyroid leads to a lack of the production of thyroid hormone. Sensitivity to cold is increased, a person can feel fatigue, depression and impaired memory. Hypothyroidism can also be manifested as excessive daytime sleepiness, especially in children.

Poor circulation and sleep

Problems with circulation can lead to the delayed sleep onset, as the person might have trouble falling asleep due to coldness in hands and feet. They may report numbness in limbs upon waking due to severe cold, even when the ambient temperature is warm.

These people need special limb stimulation, like a massage or light exercises just before bed. Even though exercises before sleep are usually not recommended, this rule stands for those whose blood circulation is fast, not those who struggle with warming up in normal temperatures. Exercising many times throughout the day, swimming, walking, and cycling can help improve your circulation.

Raynaud’s disease and sleep

This disease is most frequently found in those who live in colder climates. Their fingers, hands, and feet seem impossible to warm. Upon warming, they have a prickling sensation or even pain in their extremities, after which the skin turns red, just like after a long time of playing in the snow. Only without snow.

Raynaud’s disease is in its basis a natural process that happens to all of us when exposed to extremely low temperatures – blood vessels narrow down as blood rushes to our core body. This happens so that our vital organs could remain safe temperature-wise. However, in Raynaud’s disease this process happens too easily – almost as soon as a part of our body senses cold exposure. It’s not dangerous but can impair one’s sleep quality.

Multiple sclerosis and sleep

Multiple sclerosis (MS) patients have problems with the destruction of a layer of matter surrounding their neurons, which makes it difficult for the brain to send out information. Apart from the brain, spinal cord and optic nerves can be affected.

This means MS sufferers can have problems with basic body functions – vision, balance and temperature change. Their sleep can be severely impaired due to the following reasons – feeling too hot or cold regardless of thermal environment, having leg cramps at night, suffering from insomnia, restless leg syndrome or sleep disordered breathing.

How do too hot and cold temperatures affect our sleep?

Neither too hot nor cold temperatures are good for your sleep. Here’s what the negative sides of a wrong temperature are.

  • Sleep loss. When your body is too hot or too cold, you might wake up either drenched in sweat or shivering. This normally doesn’t happen but is possible in extreme temperatures. It may be difficult to fall asleep altogether.
  • There’s a decrease in REM and deep sleep (slow-wave sleep). You will lose a lot more REM sleep than deep sleep. If you keep sleeping in inadequate temperatures, you may experience REM sleep deprivation.
  • Aggravation of sleep disturbances and diseases.

Simply setting the thermostat to a pleasant temperature or sleeping with less (or more) bed covers may prevent these problems.

How to help your body regulate temperature during sleep?

Here are some things you can do to ensure you get quality sleep by minding the temperature. It is not only your body and metabolism that play a role, but also bed and covers, room temperature and your clothes.

  • Set the thermostat or AC to a thermoneutral temperature. Temperatures much higher or lower than 64F promote wakefulness.
  • Keep your windows open if the outside temperature is suitable.
  • Use natural materials for bedding and pajamas so that your body can regulate temperature through them. Artificial materials tend to trap heat and are not recommendable.
  • Dress accordingly. If you have night sweats, try sleeping without pajamas and with a thinner cover, but if you are a cold sleeper, make sure you are well tucked up.
  • Take a bath before bed. If it’s winter time, take a warm bath, but in hot summer days, you might want to decrease the temperature by a cold one.
  • Exercise during the day. This will promote healthy blood flow and proper function of all systems in your body, including thermoregulation.
  • Avoid exercise before bed, unless you have poor blood circulation. Then you might want to exercise for a couple of minutes to warm up.

Following these pieces of advice on regulating your thermal environment will help you sleep better. However, don’t forget to stick to other rules of healthy sleep habits that can improve not only your sleep but your overall life satisfaction as well.

Additional resources

  1. Thermoregulation. Encyclopaedia Britannica. https://www.britannica.com/science/thermoregulation Accessed December 29, 2018.
  2. Libert J. P. Thermal regulation during sleep. Revue neurologique. November 2003. https://www.ncbi.nlm.nih.gov/pubmed/14646797 Accessed December 29, 2018.
  3. Bach V, Telliez F, Libert J. P. The interaction between sleep and thermoregulation in adults and neonates. Sleep medicine reviews. December 2002. https://www.ncbi.nlm.nih.gov/pubmed/12505480 Accessed December 29, 2018.
  4. Onen S. H, Onen F, Bailly D, Parquet P. Prevention and treatment of sleep disorders through regulation of sleeping habits.
    Presse médicale. March 1994. https://www.ncbi.nlm.nih.gov/pubmed/8022726 Accessed December 29, 2018.
  5. Haskell E. H, Palca J. V, Walker J. M, et al. Metabolism and thermoregulation during stages of sleep in humans exposed to heat and cold. Journal of Applied Physiology. October 1981. https://www.physiology.org/doi/abs/10.1152/jappl.1981.51.4.948 Accessed December 29, 2018.
  6. Celmer L. Sleep deprivation disrupts regulation of body heat. Sleep Education. December 12, 2012. http://sleepeducation.org/news/2012/12/18/sleep-deprivation-disrupts-regulation-of-body-heat Accessed December 29, 2018.

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