Bathing 1-2 hours before bedtime in water of about 104-108.5 degrees Fahrenheit (40-42.5 degrees Celsius) can significantly improve the quality and efficiency of your sleep, according to a review of previous studies, published in the journal Sleep Medicine Reviews.
Before-bedtime bathing can significantly increase your chances of getting a good night’s rest. Image credit: Michelle Maria.
“When we looked through all known studies, we noticed significant disparities in terms of the approaches and findings,” said study lead author Shahab Haghayegh, a Ph.D. candidate at the University of Texas at Austin.
“The only way to make an accurate determination of whether sleep can in fact be improved was to combine all the past data and look at it through a new lens.”
Haghayegh and colleagues searched PubMed, CINAHL, Cochran, Medline, PsycInfo, and Web of Science databases.
They extracted pertinent information from publications meeting predefined inclusion and exclusion criteria to explore the effects of water-based passive body heating on a number of sleep-related conditions: sleep onset latency, total sleep time, sleep efficiency, and subjective sleep quality.
The search yielded 5,322 candidate articles of which 17 satisfied inclusion criteria, with 13 providing comparable quantitative data for analyses.
The researchers found that an optimum temperature of between 104 and 108.5 degrees Fahrenheit improved overall sleep quality.
When scheduled 1-2 hours before bedtime, it can also hasten the speed of falling asleep by an average of 10 minutes.
“Much of the science to support links between water-based body heating and improved sleep is already well-established,” the scientists said.
“For example, it is understood that both sleep and our body’s core temperature are regulated by a circadian clock located within the brain’s hypothalamus that drives the 24-hour patterns of many biological processes, including sleep and wakefulness.”
The study authors also found the optimal timing of bathing for cooling down of core body temperature in order to improve sleep quality is about 90 minutes before going to bed.
“Warm baths and showers stimulate the body’s thermoregulatory system, causing a marked increase in the circulation of blood from the internal core of the body to the peripheral sites of the hands and feet, resulting in efficient removal of body heat and decline in body temperature,” they explained.
“Therefore, if baths are taken at the right biological time, they will aid the natural circadian process and increase one’s chances of not only falling asleep quickly but also of experiencing better quality sleep.”
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Shahab Haghayegh et al. 2019. Before-bedtime passive body heating by warm shower or bath to improve sleep: A systematic review and meta-analysis. Sleep Medicine Reviews 46: 124-135; doi: 10.1016/j.smrv.2019.04.008
