Don’t let poor sleep ruin your life

Staying cool about sleep. How our environment affects our sleep

Staying cool about sleep. How our environment affects our sleep

Many things change about our bodies during sleep:

  • Our heart rate is slower than normal
  • Our breathing slows down
  • Our muscles relax
  • We undergo changes in how our body can control and respond to changes in ambient (the environmental) and core (internal body) temperature.

By learning more about how these changes affect our sleep - and what effect our sleep has on them - we can adapt our environment and routines. This can lead to a more efficient, deeper and comfortable sleep and result in many health benefits.

Core temperature affects sleepiness

Core body temperature follows a circadian rhythm, meaning that it rises and falls across a 24 hour cycle.

It’s widely accepted that a drop in core body temperature is a signal for our bodies to prepare for sleep - this is a deeply ingrained characteristic that is common across a number of mammals 1.

The reasons underpinning the alignment of core temperature changes to the day/night cycle are rather complex. In the run up to sleep, the body’s temperature starts to fall and this is linked to a reduction in the time it takes to fall asleep 2.

During the course of the night, there is a drop in core temperature of about 1°C 3, with the lowest body temperature occurring in the early morning.

Conversely, increases in core temperature during sleep appear to promote waking 4. About two hours before we wake, our core body temperature begins to rise and it continues to rise throughout the day, peaking in the early evening.

It has also been observed that people living with insomnia have a core body temperature rise and fall that isn’t in line with their chosen bed time 3.

For core temperature changes to happen, our bodies need to be able to retain or lose heat effectively.

Humans do this via the skin, which has a network of blood vessels running under it. Blood vessels open up (a process called vasodilation) or narrow down (a process called vasoconstriction) depending on whether core body temperature needs to decrease or increase.

If a core body temperature decrease is required, heat can be lost through the peripheral skin (the skin covering the arms, hands, legs and feet) 3.

In this way, the skin acts as a ‘radiator’ for excess body heat. While this may sound out of place in an article about sleep, we can use this feature of our bodies to get a better night’s sleep.

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Heating yourself up to cool yourself down

How do we achieve a drop in core body temperature, so that we fall asleep faster? The answer might surprise you. It’s not to expose yourself to cold, but to warm up your skin up before getting into bed. Warming the peripheral skin causes the blood vessels to dilate so more heat escapes through their walls and we lose body heat faster. Therefore when you go to bed, you’re already in the process of cooling down. You can achieve this by:

  • Taking a warm bath, shower, or just a foot bath approximately 1.5-2 hours before your chosen bedtime. This can help you fall asleep faster 5.
  • Exercising a few hours before bed. it’s another useful way of generating body heat, which leads to a drop in core body temperature after the exercise.

Now that we know how to use temperature adjustments to ease falling asleep, let’s look at the role temperature plays in helping us stay asleep.

Using the temperature to get the best possible sleep

A bedroom environment that is either too hot or too cold can lead to sleep disturbances 6 and can affect the stages of sleep the body must go through to repair itself and feel fully rested 4.

Therefore, by paying some attention to our sleeping conditions, we can help ourselves to get better, deeper sleep.

What’s the ideal room temperature?

The consensus among scientists is that the temperature in the bedroom should be around 16-18°C. This allows you to lose body heat throughout the night, which is essential for good sleep 7.

The room temperature is not the only factor you need to consider. The temperature under your bedclothes is also important. This needs to be roughly between 27 and 32°C 89 to ensure good sleep.

The humidity of the air is also important. High humidity values, particularly in hot climates, have a negative impact on deep sleep and increase wakefulness 10.

It’s also worth noting that your temperature preference is also affected by variables such as the time of year and your sex. We can tolerate higher sleep temperatures during summer more than winter and women prefer a slightly higher bed temperature than men 11.

It can be useful to experiment with different pre-sleep activities, bedding and clothing materials, as well as room humidity values, to determine what works for you.

In short:

You may be able to reduce the time it takes to fall asleep by doing some of the following before bed:

  • Take a warm shower or bath
  • Warm up your feet
  • Exercise a few hours before lights out

You may also get a better night’s sleep by:

  • Keeping your bedroom at a comfortable temperature
  • Trying to keep a temperature of around 30°C in bed (Experiment with different bedding and clothing materials)
  • Using a dehumidifier if necessary

References


  • Edward C. Harding, Nicholas P. Franks, and William Wisden. The Temperature Dependence of Sleep. Frontiers in Neuroscience, 13:336, April 2019. ISSN 1662-453X. doi: 10.3389/fnins.2019.00336.

  • Saul S Gilbert, Cameron J van den Heuvel, Sally A Ferguson, and Drew Dawson. Thermoregulation as a sleep signalling system. Sleep Medicine Reviews, 8(2):81–93, April 2004. ISSN 10870792. doi: 10.1016/S10870792(03)00023-6

  • Muzet, J. P. Libert, and V. Candas. Ambient temperature and human sleep. Experientia, 40(5):425–429, May 1984. ISSN 0014-4754, 1420-9071. doi: 10.1007/BF01952376.

  • Kazue Okamoto-Mizuno and Koh Mizuno. Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology, 31(1):14, December 2012. ISSN 1880-6805. doi: 10.1186/1880-6805-31-14.

  • Roy J.E.M. Raymann, Dick F. Swaab, and Eus J.W. Van Someren. Skin temperature and sleep-onset latency: Changes with age and insomnia. Physiology & Behavior, 90(2-3):257–266, February 2007. ISSN 00319384. doi: 10.1016/j.physbeh.2006.09.008.

  • L. Lan, K. Tsuzuki, Y.F. Liu, and Z.W. Lian. Thermal environment and sleep quality: A review. Energy and Buildings,149:101–113, August 2017. ISSN 03787788. doi:10.1016/j.enbuild.2017.05.043.

  • Peter Strøm-Tejsen, Sigrid Mathiasen, Marlene Bach, and Steffen Petersen. The effects of increased bedroom air temperature on sleep and next-day mental performance. page 8.

  • Shreyas S. Joshi, Thomas J. Lesser, Jonathan W. Olsen, and Bruce F. O’Hara. The importance of temperature and thermoregulation for optimal human sleep. Energy and Buildings, 131:153–157, November 2016. ISSN 03787788. doi: 10.1016/j.enbuild.2016.09.020.

  • Chin Moi Chow, Mirim Shin, Trevor J Mahar, Mark Halaki, and Angus Ireland. The impact of sleepwear fiber type on sleep quality under warm ambient conditions. Nature and Science of Sleep, Volume 11:167–178, August 2019. ISSN 1179-1608. doi: 10.2147/NSS.S209116.

  • Li Lan and Zhiwei Lian. Ten questions concerning thermal environment and sleep quality. Building and Environment, 99:252–259, April 2016. ISSN 03601323. doi: 10.1016/j.buildenv.2016.01.017.

  • Yanfeng Liu, Cong Song, Yingying Wang, Dengjia Wang, and Jiaping Liu. Experimental study and evaluation of the thermal environment for sleeping. Building and Environment, 82:546–555, December 2014. ISSN 03601323. doi:10.1016/j.buildenv.2014.09.024.

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