“When we looked through all known studies, we noticed significant disparities in terms of the approaches and findings,” said Shahab Haghayegh, 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.”
In collaboration with the UT Health Science Center at Houston and the University of Southern California, the researchers reviewed 5,322 studies.
Meta-analytical tools were used to assess the consistency between relevant studies and showed that an optimum temperature of between 104 and 109 degrees Fahrenheit (40-42 degrees Celsius) improved overall sleep quality. The paper explaining the method was recently published in the journal Sleep Medicine Reviews.
When scheduled one-two hours before bedtime, it can also hasten the speed of falling asleep by an average of 10 minutes.
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 average person’s circadian cycle is characterised by a reduction in core body temperature of about 0.5 to 1 Fahrenheit around an hour before usual sleep time – dropping to its lowest level between the middle and later span of night-time sleep. It then begins to rise, acting as a kind of a biological alarm clock wake-up signal.
The researchers 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.
“If baths are taken at the right biological time – 1-2 hours before bedtime – 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,” read the findings.