BALTIMORE—Partial sleep restriction increased plasma leptin levels in healthy adults with ad libitum access to food, according to research presented at the 22nd Annual Meeting of the Associated Professional Sleep Societies. Greater leptin increases were observed among women, compared with men.
Norah Simpson and colleagues measured morning levels of leptin, an adipocyte-derived, proinflammatory hormone that is associated with obesity, in 138 healthy adults (mean age, 30; mean BMI, 24.6; 47% males). After two nights of baseline sleep (10 hours in bed per night), participants were randomized to either five nights of sleep restriction (four hours in bed per night; n = 119) or control sleep (10 hours in bed per night; n = 19). Participants received three meals per day, plus an optional evening snack during sleep restriction. Additional snack food was available ad libitum throughout the study. Blood samples were collected between 9 and 11 am following the second night of baseline sleep and the fifth night of sleep restriction, and leptin levels were quantified with a standard radioimmunoassay.
Baseline leptin levels were strongly correlated with BMI. No differences were observed between the two groups on baseline leptin levels, age, gender, or BMI. Demographic variables associated with higher leptin levels at baseline were female gender, African American ethnicity, higher BMI, and older age.
Leptin Response After Sleep Restriction
Leptin levels increased significantly from baseline to end point in the sleep restriction group, observed Ms. Simpson, a graduate student in the Division of Sleep and Chronobiology, Department of Psychiatry, at the University of Pennsylvania School of Medicine in Philadelphia, and coauthors. However, changes in the control group were not significant.
The only demographic variable associated with a differential response to sleep restriction was gender. Women had a significantly greater increase in leptin, compared with men, after sleep restriction. “A repeated-measures analyses of variance confirmed both the main effect of sleep restriction, as well as the interaction effect of sleep restriction and sex,” noted the investigators. These results remained significant after controlling for BMI.
Is Food Intake a Possible Explanation?
Previous studies have found that leptin levels decrease after sleep restriction. “One possible explanation for [our] finding is that participants in the sleep-restriction condition had higher food consumption levels, due to the increased access to food,” the researchers commented. “However, food intake was not adequately quantified in the study to ensure this was the case.” Other factors, including stress modulation, may have influenced leptin responses.
Future studies will need to quantify food intake and track the 24-hour profile of leptin during sleep restriction, stated Ms. Simpson and colleagues. “These results raise further questions about the putative role of leptin in the potentially modifiable relationship between sleep restriction and obesity,” they concluded.
—Marguerite Spellman