Short Sleep Duration is Inversely Associated with the Prevalence of Underweight in a Young Japanese Population

Many studies have shown that sleep disorders including short sleep duration are associated with obesity. However, evidence regarding the association between sleep duration and underweight is limited and inconsistent. This study investigated the relationship between sleep duration and body mass index (BMI), focusing on the prevalence of underweight and obesity in a young Japanese population.

We enrolled 12,496 students at Ehime University between April 2015 and May 2017. Information on sleep duration, sleep disorders, alcohol consumption, smoking, and exercise habits were collected using self-reported questionnaires. Logistic regression analysis was used to estimate crude odds ratios (ORs) and 95% confidence intervals (CIs) for the association between sleep duration and BMI, using 7-<8 hours as the reference. Age, sex, drinking habits, smoking, exercise habits, and sleep disorders were considered confounding factors.

The prevalences of underweight (BMI <18.5) and obesity (BMI ≥25) were 14.3% and 10.5%, respectively. Short sleep durations remained significantly positively associated with obesity (6-<7 h: OR 1.19, 95% CI: 1.03-1.37 and 9 h or more OR 0.74, 95% CI: 0.56-0.97; p for trend = 0.001). Longer sleep duration remained significantly positively associated with underweight (6-<7 h: OR 0.86, 95% CI: 0.76-0.99; 8-<9 h: OR 1.15, 95% CI: 1.01-1.31; and 9 h or more: OR 1.40, 95% CI: 1.16-1.69; p for trend = 0.001). In men but not women, sleep duration was independently inversely associated with obesity (9 hours or more OR: 0.70; 95% CI: 0.50-0.96; p = 0.003). Positive association between sleep duration (9 hours or more) and underweight was found (men OR: 1.47; 95% CI: 1.12-1.92; p = 0.001, and women OR: 1.37; 95% CI: 1.04-1.79; p = 0.001).

Sleep duration was significantly positively associated with the underweight and inversely associated with obesity in the young Japanese population.