A warm bath 1-2 hours before bedtime can significantly improve sleep

A warm bath about 1-2 hours before bedtime can significantly improve your sleep, according to a new study by biomedical engineers at The University of Texas at Austin.

The research team analyzed 5,322 studies to explore the effects of water-based passive body heating (PBHWB) on sleep onset latency, wake after sleep onset, total sleep time, sleep efficiency, slow wave sleep, and subjective sleep quality.

Meta-analytical tools were then used to assess the consistency between relevant studies.

“When we looked through all known studies, we noticed significant disparities in terms of the approaches and findings,” said Shahab Haghayegh, a Ph.D. candidate in the Department of Biomedical Engineering and lead author on the paper.

“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.”

The researchers found that a temperature of 40–42.5 °C was associated with both improved self-rated sleep quality and sleep efficiency. When scheduled 1 to 2 hours before bedtime, it also significantly shortened sleep onset latency.

According to the abstract of the study, “these findings are consistent with the mechanism of PBHWB effects being the extent of core body temperature decline achieved by increased blood perfusion to the palms and soles that augments the distal-to-proximal skin temperature gradient to enhance body heat dissipation.”

Body temperature plays an important role in the regulation of the sleep/wake cycle. Previous research has shown that fluctuations in internal body temperature regulate the body’s circadian rhythm.

An average person’s circadian cycle is characterized by a slight drop in core body temperature about an hour before usual time, dropping to its lowest level between the middle and later span of nighttime sleep.

Warm baths or showers stimulate the body’s thermoregulatory system, increasing the circulation of blood from the internal core of our body to the peripheral sites of the hands and feet. The result is an efficient removal of body heat and decline in body temperature.

The study was published in the journal Sleep Medicine Reviews (citation below).

Journal Citation

“Before-bedtime passive body heating by warm shower or bath to improve sleep: A systematic review and meta-analysis”
Shahab Haghayegh, SepidehKhoshnevis, Michael H.Smolensky, Kenneth R.Diller, Richard J.Castriotta
Sleep Medicine Reviews Volume 46, August 2019, Pages 124-135