Short sleep duration at night in 2.5-year-old children is associated with childhood obesity at age 5.5 years: The Japanese children cohort study

Obesity in children contributes to higher risks of various chronic diseases in adulthood and the prevalence has increased worldwide including Japan. This study aims to examine the association between sleep duration at night in children aged 2.5 years and the subsequent risk of obesity at age 5.5 years. This study is embedded in the Longitudinal Survey on Babies Born in the 21st Century, which recruited families who had a child born in Japan in 2001. The multivariable logistic regression models were applied to calculate odds ratios (OR) and 95 % confidence intervals (CI) of childhood obesity at 5.5 years, defined as percentage of overweight (POW) ≥ 20 % and body mass index (BMI) ≥ 95th percentile of this study population according to sleep duration at night collected at 2.5 years child age. Among 25,378 children, 2.6 % and 3.7 % were obese at age 5.5 years defined by POW and BMI respectively. Compared with night sleep duration > 11 h/d, shorter sleep durations in 2.5 years-old children were associated with higher risk of obesity at 5.5 years; the multivariable ORs (95 %CI) were 1.05 (0.81-1.35), 1.23 (0.93-1.62) and 1.54 (1.04-2.31) for sleep duration 10, 9 and ≤ 8 h/d, respectively; p-trend = 0.03. The observed association differed according to the children (child's sex, napping habits, and children frequently play at park), and family characteristics (mother's age at delivery and mother's level of education). Short night sleep duration among girls aged 2.5 years was associated with risk of obesity at age 5.5 years, suggesting the importance of sufficient sleep duration at night for the prevention of obesity.