Wrist-worn accelerometer measured sleep fragmentation and obesity risk: Socioeconomic gradients and mediation by...

Sleep fragmentation is a recognized risk factor for obesity, yet whether socioeconomic status moderates this association and whether chronic stress responses mediate it remain unclear.

We analyzed 3007 U.S. adults (≥18 years) from NHANES 2013-2014 with valid wrist-worn accelerometer data, representing approximately 132.7 million adults nationwide. Sleep fragmentation was quantified as wake minutes per hour (WASO/h) and awakenings per hour (AWAKE/h) using a Hidden Markov Model. Outcomes were general obesity (Body Mass Index, BMI) and central obesity (Body Roundness Index, BRI). Moderation by a composite socioeconomic status index (poverty income ratio, education, insurance) and mediation by Allostatic Load Index were evaluated using survey-weighted multinomial logistic regression and moderated mediation models.

Higher sleep fragmentation was associated with greater odds of obesity (WASO/h: OR, 1.32; 95% confidence interval (CI), 1.15-1.50; AWAKE/h: OR, 1.52; 95% CI, 1.27-1.83; both P < .001), with similar patterns for Body Roundness Index-defined obesity. These associations were stronger among higher-socioeconomic status adults and less pronounced in middle-socioeconomic status groups. Moderated mediation analyses indicated partial mediation by Allostatic Load Index, with significant indirect effects in high-socioeconomic status groups accounting for 13%-16% of the total association. Results were consistent across sensitivity analyses including multiple imputation, alternative Allostatic Load Index definitions, and additional adjustment for sleep duration and physical activity.

Sleep fragmentation was significantly associated with increased risk of both general and central obesity, with socioeconomic heterogeneity in effect magnitude. Chronic stress pathways partially explained this relationship, particularly among higher-socioeconomic status adults, suggesting that incorporating sleep quality assessment may benefit obesity prevention across diverse socioeconomic status contexts.