NEW YORK CITY — A pooled analysis of two randomized crossover trials published in the Annals of Internal Medicine found that reducing nightly sleep by approximately 1.5 hours over six weeks was associated with increases in body weight, waist circumference, and sedentary time in adults.

The study included 95 adults aged 20 and older who typically slept seven or more hours per night. Participants were assigned to either maintain their usual bed and wake times, ensuring at least seven hours of sleep, or to reduce their nightly sleep by about 1.5 hours by delaying bedtime for six weeks. After a multi-week washout period, participants switched to the other study condition. Sleep duration differed by 78.4 minutes between the groups, a factor monitored through wrist actigraphy and nightly sleep diaries.

During the period of reduced sleep, participants experienced an average body weight increase of 0.45 kg (1 lb) over six weeks. Waist circumference increased by 0.52 cm, and whole-body volume increased by 0.56 L. The analysis also showed that sleep reduction led to an increase in sedentary time of 17.2 minutes per day, after adjusting for the time spent in bed.

Mechanistic analysis revealed elevated leptin levels, with a difference of 2.03 ng/mL, during periods of sleep reduction. However, the study did not find differences in ghrelin or GLP-1 levels between the groups. One of the trials involved women and focused on cardiometabolic risk factors, while the other recruited both men and women and centered on measures of energy balance regulation. The study measured metabolic characteristics only in a morning fasted state.

Researcher Marie-Pierre St-Onge stated, "The magnitude of change mirrors population trends in annual weight gain during early and middle adulthood and may contribute to increased risk for obesity and cardiometabolic disorders over time." She added, "If replicated, this finding can have important clinical relevance, as greater time spent sedentary may contribute to adiposity gains and predicts elevated risk for cardiometabolic diseases and mortality." St-Onge said, "These findings highlight the importance of discussing sleep duration at healthcare encounters and support guidance to maintain adequate sleep duration to improve weight management and obesity prevention across the lifespan." Regarding mechanisms, she stated, "Although a topic of debate, one potential explanation for this effect is dysregulation of hormonal control of appetite." She also noted, "In addition, although this study reflects a long intervention period for the field, the 6-week duration of [sleep restriction] may have been too short to observe substantial changes in body tissue distribution."