Durk Pearson & Sandy Shaw's®
Life Extension NewsTM
Vol. II, No. 6, October 1999

In a new study of how long it takes to fall asleep, the authors find that the degree of dilation of blood vessels in the skin of the hands and feet is the best physiological predictor for the rapid onset of sleep.

Eight healthy young men were given melatonin or bright light, or both, in the evening, while another ten healthy young men were given a large, carbohydrate-rich meal in either the morning or evening, to test the effects on latency to sleep onset. The researchers found that the greater the distal vasodilation (i.e., the warmer the feet) in the late evening, the shorter was the time to fall asleep. The authors note that this vasodilation can be affected by a number of factors. For example, vasodilation can occur as a result of turning out the light, lying down (which redistributes heat from the core to the periphery), and endogenous increase of melatonin.

They suggest that "[s]ome sleep disorders (particularly those associated with aging and somatic illness) may be secondary to an inability to vasodilate and prepare the body for sleep."

Other possible ways to warm your feet and perhaps fall asleep faster include hot water bottles or an electric blanket at the foot of your bed, L-arginine plus choline supplementation, and niacin supplementation.

Krauchi et al, "Warm Feet Promote the Rapid Onset of Sleep," Nature 401:36-37 (1999).

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