Dr's Casebook: A bath before bed helps sleep

Dr Keith Souter writes: People are often told to have a warm bath before going to bed, perhaps adding bubbles or aromatic oils to aid relaxation. It may seem too simple a thing to do, yet there does seem to be a scientific reason why it works.

Research was done by biomedical engineers at the University of Texas, working with researchers from the University of South California. They used a technique to review over 5,000 other studies that link the effects of showers and bathing on sleep. They measured various sleep factors, including sleep time, time to drop off, subjective sleep quality and sleep efficiency.

Sleep is complex and very subjective, as people gauge their sleep in different ways. Thus, someone may have good, long uninterrupted sleep, yet still say they have poor quality sleep and vice versa.

They found that a common temperature of 104 to 107 degrees F (about 40-42 C) was the ideal temperature to promote improved sleep quality. They also found that when the bath is about 90 minutes before bedtime the rate and speed of falling asleep increases by up to ten minutes. They suggest that 15 minutes is probably the best length of time in the bath. Hotter than this is too hot and counter-productive. It can also dry the skin.

The reason is to do with the hypothalamus in the brain. It is responsible for regulating body temperature. In turn, body temperature regulates the sleep and waking cycle. Body temperature varies throughout the day, so that the average body temperature is about two or three degrees Fahrenheit higher in the afternoon and late evening than during sleep time, when it is lowest. The average person’s core body temperature decreases by up to one degree Fahrenheit an hour before bedtime and drops to the lowest level between the middle and late stages of the sleep period.

A bath 90 minutes before bedtime helps the hypothalamus to cool the core temperature to make sleep faster and of better quality.