Highlight
A pooled analysis of two randomized crossover trials showed that six weeks of moderately short sleep (1.5 hours less than usual per night) in adults at elevated cardiometabolic risk resulted in modest but consistent increases in body weight, waist circumference, whole-body volume, and leptin levels. Additionally, participants exhibited increased sedentary time during sleep restriction compared with adequate sleep periods.
This study is among the first to evaluate the causal effect of chronic mild sleep insufficiency on detailed measures of body composition using magnetic resonance imaging (MRI), providing mechanistic insight into how prolonged short sleep may contribute to obesity and cardiometabolic risk.
Study Background
Obesity is a global health epidemic linked to increased risk for cardiovascular disease, type 2 diabetes, and other chronic conditions. Insufficient sleep has long been associated epidemiologically with obesity and weight gain, yet the causal relationship remains incompletely defined. Prior sleep restriction studies often involved extreme or very short sleep durations over acute periods, limiting generalizability to real-world chronic mild sleep insufficiency often encountered by adults.
Understanding whether sustained, modest sleep restriction causally contributes to weight gain, and whether such effects vary by gender or menopausal status, has important implications for preventive strategies targeting sleep behaviors to mitigate cardiometabolic disease burden.
Study Design
This analysis pooled data from two randomized crossover trials registered at ClinicalTrials.gov (NCT02960776 and NCT02835261). The studies recruited 95 adults aged 20 years or older who were at elevated cardiometabolic risk and habitually slept seven or more hours per night.
Participants underwent two 6-week intervention periods: sustained adequate sleep (AS) and sleep restriction (SR) of 1.5 hours less sleep per night than the individual’s habitual sleep duration. The crossover design incorporated a multiweek washout between interventions to minimize carryover effects.
Primary outcomes included body weight, waist circumference, whole-body volume, and adiposity assessed by MRI. Secondary outcomes encompassed energy balance behaviors such as sedentary time and relevant biomarkers including leptin levels.
Key Findings
The sleep restriction intervention reduced nightly sleep duration by 78.4 minutes (95% CI, −83.5 to −73.3 minutes) compared with adequate sleep. This reduction was sustained over the 6-week period.
Compared with adequate sleep, sleep restriction was associated with statistically significant increases in body weight (+0.45 kg, 95% CI 0.33 to 0.57), waist circumference (+0.52 cm, 95% CI 0.25 to 0.79), and whole-body volume (+0.56 liters, 95% CI 0.19 to 0.93), indicating measurable increases in adiposity and central fat accumulation.
Leptin concentrations, a hormone associated with satiety and adiposity, were elevated during sleep restriction (2.03 ng/mL, 95% CI 0.38 to 3.68), supporting a biological mechanism linking insufficient sleep to altered energy homeostasis.
Behaviorally, participants in the sleep-restricted condition spent 17.2 more minutes per day sedentary (95% CI 11.7 to 22.7 minutes), suggesting that reduced physical activity may contribute to positive energy balance during mild chronic sleep loss.
Study Limitations and Strengths
The intervention duration of six weeks, while longer than many prior trials, may still be insufficient to observe more pronounced changes in body composition or long-term metabolic consequences. Additionally, the modest sample size limited the power to detect differences by demographic subgroups such as sex and menopausal status.
The crossover design strengthens causal inference by controlling interindividual variability. Use of MRI for adiposity assessment provided precise quantification beyond simple anthropometric measures. However, generalizability may be limited to adults at elevated cardiometabolic risk habitual to sufficient sleep at baseline.
Expert Commentary
This pooled analysis adds to accumulating evidence that even modest chronic reductions in sleep duration can promote weight gain and adiposity, potentially via increased sedentary behaviors and dysregulated energy balance hormones such as leptin. The findings underscore the importance of sleep as a modifiable lifestyle factor in obesity prevention.
Clinicians managing patients with obesity or cardiometabolic risk should consider incorporating sleep assessment and counseling into routine care. Future studies with longer duration and more diverse populations are needed to delineate mechanisms further and evaluate intervention strategies.
Conclusions
Prolonged exposure to moderately short sleep, defined as approximately 1.5 hours less than habitual sleep over six weeks, is causally associated with small but significant increases in body weight, central adiposity, and leptin levels. Increased sedentary time during sleep restriction likely contributes to positive energy balance.
Weight management and cardiometabolic disease prevention programs should recognize and integrate sleep extension and improvement strategies as part of comprehensive lifestyle interventions. Ensuring adequate sleep may represent an accessible and impactful avenue to assist in curbing the obesity epidemic and improving metabolic health.
Funding and Clinical Trial Registration
This research was supported by the National Institutes of Health and the American Heart Association. The included clinical trials are registered at ClinicalTrials.gov under identifiers NCT02960776 and NCT02835261.
References
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