Rather than counting sheep, relaxing in a bubble bath before bed could combat insomnia.
Indulging in an evening bath or shower an hour-and-a-half before you turn in boosts the time spent asleep and the quality of shut eye, research suggests.
Experts said water temperature of 40-to-42.5°C (104-to-108.5°F) is ‘ideal’ and speeds up sleep’s onset by up to 10 minutes.
Warm baths and showers redirect circulation to the hands and feet, which causes a drop in core body temperature, the researchers claim.
This triggers the body’s internal clock into thinking it’s time for sleep, with body temperature naturally reducing in the run up to bedtime.
The research was carried out by The University of Texas at Austin and led by Dr Shahab Haghayegh, of the department of biomedical engineering.
Insomnia affects up to 35 per cent of adults in the US to some extent, according to Sleep Education. In the UK, a third of adults claim to have insomnia, statistics show.
In the short term this can make sufferers feel fatigued. But over time, a lack of shut eye can lead to depression and even heart disease.
‘Water-based passive body heating’, such as warm shower or bath, is often recommended to combat insomnia, the researchers wrote in the journal Sleep Medicine Reviews.
However, how or why this occurs was relatively unclear.
The researchers therefore analysed 13 studies that investigated how a shower or bath affects sleep.
‘When we looked through all known studies, we noticed significant disparities in terms of the approaches and findings.’ Dr Haghayegh said.
‘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.’
Results revealed having an evening bath or shower at 40-to-42.5°C improved the participants’ self-reported sleep quality.
It also boosted their sleep efficiency, which is defined as the amount of time spent asleep relative to how long you lie in bed.
When this was scheduled for an hour or two, or an average of 90 minutes, before bed, it significantly shortened the time it took them to nod off.
Core body temperature regulates our sleep-wake cycle.
It peaks during the late afternoon and is lowest towards the end of sleep.
When our temperature rises, it acts like nature’s alarm clock.
Perhaps surprisingly, a warm bath or shower lowers our core temperature by directing blood flow to our peripheral areas, like the hands and feet.
This helps the body clock along, leading to a faster sleep time and a better quality of shut eye.
The researchers stress further studies are required to confirm the optimal timing and duration of an evening bath or shower to best benefit sleep.
They are looking into making a bed that controls a person’s temperature throughout the night.