Wearing socks to bed may just help people fall asleep. That is because the body appears to prepare for sleep by widening the blood vessels in the hands and feet to help radiate body heat away, according to a study by Anna Wirz-Justice of the Psychiatric University Clinic in Basel, Switzerland.

This phenomenon is closely related to the release of hormones like melatonin, which regulate sleepiness and wakefulness. Warming the feet with socks or a hot water bottle and then removing the socks or bottle would promote this dilation, says Wirz-Justice. But most people go through the process naturally and would not need socks or a water bottle to help them sleep. The researchers did not directly test whether socks or water bottles promoted sleep. But they did analyse data from 18 healthy young men who participated in sleep studies. The results suggest blood vessel dilation in the hands and feet in late evening and resulting heat loss are closely linked to falling asleep ( Nature , Vol 400, No 6748).