Sleep and lifestyle in young adult monozygotic twin pairs discordant for body mass index.

OBJECTIVES:The causal nature of the sleep-obesity association is unclear. To control for potential confounding by genes and shared environment, we studied monozygotic twin pairs discordant for body mass index (BMI). First, we investigated sleep in relation to BMI. Second, we examined associations of objective and subjective sleep duration and sleep debt (objective or subjective sleep duration minus subjective sleep need) with eating behaviors and physical activity (PA). DESIGN:Cross-sectional study. SETTING:Finnish twins in everyday life circumstances. PARTICIPANTS:Seventy-four healthy young adult monozygotic twin pairs, of whom 36 were BMI-discordant (∆BMI ≥ 3 kg/m2). MEASUREMENTS:Clinical measurements estimated BMI and body composition. Sleep, eating, and PA behaviors were measured by self-report and actigraphy. RESULTS:Compared to co-twins with lower BMI, co-twins with higher BMI reported shorter sleep (P = .043), more snoring (P = .0093), and greater tiredness (P = .0013) and trended toward eveningness (P = .036). Actigraphy-measured sleep duration correlated highly within BMI-discordant twin pairs (r = 0.63, P = .004). Subjective sleep debt was consistently positively associated with disinhibited eating and binge eating, but not with BMI. Subjective and objective sleep debt had negative correlations with moderate-to-vigorous PA. CONCLUSIONS:Twins with higher BMI showed less favorable sleep characteristics than their co-twins with lower BMI. Subjective sleep debt is a potential target for intervention to reduce eating and PA behaviors that promote weight gain. Experimental studies could elucidate mechanisms underlying tiredness in individuals with higher BMI and investigate causal relationships between sleep debt, BMI, and lifestyle.