- Researchers at Kyushu University in Japan measured sleep quality in 23 people
- Found optimum time for people to sleep faster and less likely to wake in the night
- Around one in three people in the UK regularly experiences problems sleeping
Millions of insomniacs swear by a hot bath before bedtime to help them get a good night’s sleep.
Now scientists have found the optimum time they should spend soaking to ensure the method works – 15 minutes.
Taking a shower – or bathing for less than a quarter of an hour – does not have the same effect.
Researchers at Kyushu University in Japan measured sleep quality in 23 men and women.
The results, published in the Journal of Physiological Anthropology, showed that when they relaxed in a hot bath for 15 minutes or more a couple of hours before bedtime they got to sleep faster and were less likely to wake in the night.
Scientists have found the optimum time they should spend soaking to ensure the method works – 15 minutes
Around one in three people in the UK regularly experiences problems sleeping. Insomnia is thought to cost our economy in the region of £34 billion a year because of lost productivity.
And the NHS dishes out an estimated £50 million of sleeping pills every year to patients who lie awake a night.
In the new study volunteers were told to take a quick shower, a short dip in the bath or a long, hot soak lasting 15 minutes or more – and at least 90 minutes before bedtime –on different nights. They took their temperature before and after, and again when they were about to nod off.
Meanwhile, a motion-sensing gadget on their wrist tracked when they fell asleep. The results showed that when they had a long soak, the recruits nodded off in an average of 12 minutes.
But after a quick dip it took 16 minutes and when they had a shower it was 20. They also slept more deeply, with fewer movements detected during the night.
Scientists think long baths work better because they raise the body’s core temperature more – by around 0.9C compared to just 0.3C with a shower or short soak.
This means it then has to cool down a lot more for the body to be able to get to sleep.
Experts think it’s the size of this cooling effect – rather than the specific core temperature – which makes us drowsy. But they say that it is crucial to have a bath at least an hour and a half before going to bed to allow enough time for this cooling process to take place.
In a report on their findings, researchers said: ‘A greater decrease in core temperature after bathing appears to be important for improving sleep onset. Our findings suggest the magnitude of the increase in body temperature from long bathing is closely associated with the ease of falling asleep.’