A bath 90 minutes before bedtime best for a good night’s sleep, experts say

Do you have trouble sleeping? Taking a bath approximately 90 minutes before sleeping may help you sleep faster and better, a new study suggests.

A team of biomedical engineers at the University of Texas and Cockrell School of Engineering may have discovered a way to help people having sleep problems. They found a simple method to help improve sleep – taking a warm bath one to two hours before sleeping.

The study, which was published in the journal Sleep Medicine Reviews, used systematic review protocols, a technique utilized to search and analyze vital data, to review thousands of studies that link water-based passive body heating or showing with warm or hot water and sleep quality.

Image Credit: Dasha Petrenko / Shutterstock
Image Credit: Dasha Petrenko / Shutterstock

Specifically, the researches, after analyzing known studies, found that bathing in water with temperatures of about 104-109 degrees Fahrenheit, can significantly improve one’s sleep quality.

“When we looked through all known studies, we noticed significant disparities in terms of the approaches and findings. 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,” Shahab Haghayegh, a doctorate candidate in the Department of Biomedical Engineering, said in a statement.

Average temperature and timing of the warm bath helps improve sleep quality

To land to the findings of the study, the team collaborated with the University of Southern California, and the University of Texas Health Science Center to review a total of 5,322 researches.

They extracted and filtered relevant data to see the effects of water-based passive boy heating on various sleep factors. These include total sleep time, sleep onset latency, subjective sleep quality, and sleep efficiency. Sleep onset latency is how much time is needed to sleep from full wakefulness, sleep efficiency is the amount of time sleeping relative to the total length of time spent in bed trying to fall asleep, subjective sleep quality is how the person described his sleep, and sleep time, the number hours asleep.

The team assessed the consistency among the relevant researchers using meta-analytical tools. They found a common temperature of 104 to 109 degrees Fahrenheit as the ideal water temperature to promote improved sleep quality. They also found that when the warm bath is scheduled about 1 to 2 hours or approximately 90 minutes before bedtime, it increases the rate and speed of falling asleep as much as 10 minutes.

Optimal timing of bathing for cooling down of core body temperature

The hypothalamus is responsible for regulating body temperature. Body temperature is responsible for regulating the sleep and wake cycle. Body temperature varies throughout the day since it has a circadian cycle, wherein it’s about 2 to 3 degrees Fahrenheit higher in the late afternoon and late evening, than during a person is sleeping wherein it’s the lowest. The circadian cycle of an average individual involves the decrease of core body temperature, between 0.5 to 1-degree Fahrenheit an hour before bedtime, decreasing to the lowest level between the middle and late duration of sleep.

When the temperature rises, it acts as an alarm clock. The cycle of body temperature influences the sleep cycle and it’s important to attain rapid sleep onset and increased sleep efficiency.

The study helps in providing optimal timing, about 90 minutes before bedtime, for taking a bath to cool down the core body temperature, hence, making the person sleep faster and better. Taking warm baths stimulate the thermoregulatory system of the body, promoting circulation from the body core to the peripheral areas such as the hands and feet. As a result, it removes heat from the core and in turn, lowers body temperature.

Taking warm baths at the optimal designated time will help the natural circadian process to increase the likelihood of falling asleep faster, and also, having better sleep quality.

“These findings are consistent with the mechanism of water-based passive body heating (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,” the researchers note in the study.

“Nonetheless, additional investigation is required because the findings regarding PBHWB are limited by the relative scarcity of reported research, especially its optimal timing and duration plus exact mechanisms of effects,” they added.

The team is now devising a new project to formulate a commercially-viable bed system that can control the thermoregulatory function to maintain a person’s optimal temperature throughout the night.

Journal reference:

Shahab Haghayegh, Sepideh Khoshnevis, Michael H. Smolensky, Kenneth R. Diller, Richard J. Castriotta, 'Before-bedtime passive body heating by warm shower or bath to improve sleep: A systematic review and meta-analysis', Sleep Medicine Reviews, https://doi.org/10.1016/j.smrv.2019.04.008

Angela Betsaida B. Laguipo

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Angela Betsaida B. Laguipo

Angela is a nurse by profession and a writer by heart. She graduated with honors (Cum Laude) for her Bachelor of Nursing degree at the University of Baguio, Philippines. She recently completed a Master's Degree where she specialized in Maternal and Child Nursing and is now working as a clinical instructor and educator in the School of Nursing at the University of Baguio.

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