Leptin, a hormone produced by fat cells, is a signal indicating insufficient metabolic reserve and the need for consuming more calories. Low leptin levels are a signal for starvation and increased appetite.
While the hormone/sleep connection has been shown under highly controlled laboratory circumstances in past studies, Mignot and his team aimed to explore the connection in a general population sample.
During the study, the researchers examined the sleep patterns of 1,024 volunteers from the Wisconsin Sleep Cohort Study, a population-based longitudinal study of sleep disorders that began in 1989. Participants between the ages of 30 and 60 underwent nocturnal polysomnography (a test during which a number of physiologic variables are measured and recorded during sleep) and blood sampling once every four years. They also reported on their sleep habits every five years through questionnaires and six-day sleep diaries.
The researchers' data showed a 14.9 percent increase in ghrelin and a 15.5 percent decrease in leptin in people who consistently slept for five hours compared with those who slept for eight. Mignot said the results were consistent regardless of participants' gender, BMI or eating and exercise habits. "The effect must be very strong to appear in [this entire] population," he said.
"It was quite amazing that a hormone can track a person's self-reported amount of sleep so well," he added. "To my knowledge, this is the first time that a peripheral marker in the blood is shown to correlate with habitual sleep amounts in a general, normally behaving population."
The researchers also found that in people sleeping less than eight hours (74.4 percent of the sample), increased BMI was proportional to decreased sleep. They reported that a 3.6 percent increase in BMI corresponded to an average nightly sleep du
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Contact: Michelle Brandt
mbrandt@stanford.edu
Stanford University Medical Center
6-Dec-2004