Having difficulty falling asleep? Then try wearing socks and mittens in bed. The current Nature includes a report of research from the Chronobiology and Sleep laboratory of Anna Wirz-Justice, Psychiatric University Clinic in Basel, Switzerland. The group found that the degree of dilation of blood vessels in the hands and feet was one of the best predictors of the rapid onset of sleep.
Our temperature regulation systems apparently redistribute heat from the body's core to the extremities as we sleep, which encourages the release of sleep-related hormones. They suggest that warming the feet and hands might encourage the business of falling asleep.