Toasty Toes May Help You Fall Asleep

September 22, 1999 Has anyone ever told you to put on socks when you go to bed? Did they tell you it would help you fall asleep? Now there is evidence that there is some truth to this advice. Researchers at the Chronobiology and Sleep Laboratory in Basel, Switzerland, reported in the September 2, 1999 issue of the journal Nature (vol. 401, pages 36-37) that the degree of blood vessel dilation of the hands and feet are the best predictors for rapid sleep onset. The dilation of the blood vessels ("vasodilation") in the hands and feet increases the amount of heat loss. This heat loss causes a redistribution of heat throughout body and is thought to cause changes that prepare people for sleep. In the experiment, the Swiss researchers did NOT ask people to wear socks to bed. Rather, they examined the relationships between hand/feet temperature, core body temperature, heart rate, melatonin levels and the time it took men to fall asleep. The data showed that the greater the vasodilation of the hands and feet, the shorter the time that was required to fall asleep. It is possible that heating the feet (or hands) provides the brain with a signal that it is time to sleep. The researchers suggest that this mechanism may underlie an old sleep aid: a hot water bottle placed near the feet. Presumably, the hot water bottle warms up the feet and causes vasodilation which results in heat loss. The heat loss then signals the brain: "Time to sleep!" Not only does this research provide an explanation for why warm feet may help people fall asleep faster, but it suggests ways of helping people with some sleep disorders. It is possible that some sleep disorders are related to problems with vasodilation. Perhaps socks, mittens or a hot water bottle would provide a "jump start" to the heat loss process and help these people get to sleep.

Reference: Krauchi, K., Cajochen, C., Werth, E., Wirz-Justice, A., Warm feet promote the rapid onset of sleep, Nature, 401:36-37, 1999.