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How long an individual sleeps is associated with human leptin levels, according to the results of a study reported in the November 2004 issue of the Journal of Clinical Endocrinology & Metabolism. Leptin is a hormone that plays a part in balancing signals for calorie intake with energy expenditure, possibly making individuals believe that they need to consume more and potentially leading to weight gain.
The study involved 11 healthy 22-yearold men who spent 16 consecutive nights in a sleep laboratory. The 16 nights included 3 nights with an 8-hour bed time, 6 nights with a 4-hour bed time, and 7 nights with a 12-hour bed time. The results of the study indicated that, when sleep was restricted from 12-hour bed times to 4-hour bed times, maximum leptin levels were 26% lower.