Are you one of millions of people who go to bed at night with cold hands or feet? Doctors think your poor blood flow may be impairing your ability to fall asleep.

In a study published in the science journal Nature (1999; 401:36-37), scientists at the Psychiatric University Clinic in Basel, Switzerland, found that increased blood flow to the hands and feet was the best indicator of the body’s readiness for sleep. In a study that compared the effects of various “interventions,” including high carbohydrate meals and administration of the “sleep hormone” melatonin, warm feet most accurately foretold the onset of sleep.

Based on the results, the authors predict that any act that “increases temperature in the extremities” such as placing a hot water bottle on the hands or feet, or covering the feet with socks—should help induce sleep. These measures may be especially helpful for individuals with poor circulation, including the elderly.

What’s the message? If you’re having a hard time falling asleep at night, it may be time to break out the hot water bottle, or an extra blanket. Both are inexpensive and natural ways to drift off into a warm, peaceful slumber.