A systematic review of existing literature, conducted by researchers from the University of Texas at Austin, the University of Texas Health Science Centre at Houston, and the University of Southern California, has found that a 40-42.5 °C shower or bath taken 1-2 hours before bed is highly beneficial to sleep quality.
“When we looked through all known studies, we noticed significant disparities in terms of the approaches and findings,” said lead author Shahab Haghayegh from the University of Texas, 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.”
In the study, published in the journal Sleep Medicine Reviews, the researchers went through a total of 5,322 candidate articles, yielding 17 which met the established inclusion criteria, and pooled the data together to examine the effects of water-based passive body heating on sleep onset latency, total sleep time, sleep efficiency, wake after sleep onset, slow wave sleep, and subjective sleep quality.
Results showed that a 40-42.5 °C bath or shower taken 1-2 hours before bed (90 minutes were found to be optimal) allowed subjects to fall asleep, on average, 10 minutes sooner than otherwise, as well as improved overall reported sleep quality.
The basic reason why increasing body temperature prior to sleep is beneficial has to do with our circadian clocks located within the brain’s hypothalamus – both sleep and body temperature follow a 24-hour pattern, with lower body temperatures being associated with deeper sleep.
Given the above, taking a warm shower in the evening makes the body rapidly cool down afterwards, which cues the brain to start shifting gears for bedtime, therefore allowing us to fall asleep faster and sleep more soundly.
The team is now working on a bed system with a UT-patented Selective Thermal Stimulation technology, which works by optimising body temperature throughout the night to make for more restful slumber.