Any athlete who has struggled with sleep problems knows the effects of sleep deprivation on training – fatigue, lethargy and lack of motivation are common responses. Sports science has also quantified performance degradation following poor sleep.1 While the possible causes of sleep disorders are numerous, some are well-known and easy to identify, such as too much caffeine or alcohol, eating too close to bedtime, stress, and overtraining.
Other causes of sleep problems are more complex and tied to disruption of the circadian cycle or thermoregulatory issues. Continual monitoring of core body temperature with a CORE sensor can help diagnose these types of problems.
Body temperature and sleep
The circadian cycle, and sleep in particular, is strongly linked to thermoregulation.2 Core body temperature typically is at its lowest soon before waking in the morning. It naturally rises throughout the day, reaching its peak in the early or late afternoon, depending on the individual.
In the late evening, near bedtime, core temperature decreases rapidly. This is facilitated by heat being lost through the fingers, toes, and ears by means of blood vessels in the skin dilating. As core temperature plunges and skin temperature in the periphery of the body rise, melatonin secretion increases, and sleepiness quickly grows.2
The diagram below shows the clear relationship between core temperature, likelihood of sleep, and melatonin.3
Core temp and insomnia
Insomnia is sometimes associated with abnormalities in the body temperature rhythm. Difficulty in falling asleep is associated with a delay in the evening temperature drop. Early awakening is associated with core temperature starting to rise well before the preferred waking time. And waking in the middle of the night is associated with nocturnally elevated core body temperature. 3
The chart below shows the typical core temperatures of good sleepers (solid line), sleep onset insomniacs (SOI, dotted line), and early morning awakening insomniacs (EMA, dashed line).3
Continual wearing of the CORE device will help you identify your temperature cycle throughout the day and night. While most people are comfortable wearing the CORE on their heart rate strap while sleeping, CORE’s specially designed medical-grade patches are even more unobtrusive to sleep with. Data uploaded to the CORE cloud or CORE app is easily analysed to spot daily rhythms.
Solutions to temperature-related insomnia
Solutions to insomnia are complex. Sleep-onset insomnia has been successfully treated with warming the feet4 (which causes vasodilation and subsequent core temperature drop) and morning bright light (which advances the circadian rhythm, causing core temp to drop earlier in the evening)3.
Early morning awakening insomnia has been treated with evening bright light, which delays the circadian phase and delays the rise of core temperature in the morning.
The ‘hot bath’ treatment 1–4 hours before bedtime is a common insomnia treatment. But evaluating its effectiveness is complex and may be related to age and individual characteristics. Likewise, the ideal ambient temperature of the room is influenced by age and individual physiology.
Diagnosing sleep problems can be aided by continual temperature monitoring with your CORE sensor. But finding solutions to these problems, even once diagnosed, may be complicated. The references listed below are good starting points for anyone wanting to understand the complex interplay between temperature and sleep.
- Watson, Andrew M. MD, MS Sleep and Athletic Performance, Current Sports Medicine Reports: 11/12 2017 - Volume 16 - Issue 6 - p 413-418
- Okamoto-Mizuno, K., Mizuno, K. Effects of thermal environment on sleep and circadian rhythm. J Physiol Anthropol 31, 14 (2012).
- Lack LC, Gradisar M, Van Someren EJ, Wright HR, Lushington K. The relationship between insomnia and body temperatures. Sleep Med Rev. 2008 Aug;12(4):307-17. doi: 10.1016/j.smrv.2008.02.003. PMID: 18603220.
- Harding EC, Franks NP and Wisden W (2019) The Temperature Dependence of Sleep. Front. Neurosci. 13:336.