LAUSR

OBJECTIVES Given the rapid demographic transition and obesity growth in China, it is important to study how the large only-child population (≈100 million) might contribute to the obesity epidemic. This study evaluated associations of only-child status with weight and energy expenditure-related behaviors in China and examined how the associations may vary by sex and urbanicity. STUDY DESIGN Secondary analyses of nationally representative cross-sectional data from China Education Panel Survey: Junior Cohorts 2013-14, which included 19,487 students from 112 middle schools in 28 regions across China. METHODS We used propensity-score-weighted multilevel models to test associations between only-child status and weight outcomes. RESULTS Compared with sibling-sons, only-sons had higher body mass index (BMI) (Beta = 0.32, P < 0.05) and higher risks of overweight (OR = 1.24, 95% CI = [1.07-1.45]) and obesity (OR = 1.29, 95% CI = [1.02-1.64]); and spent less time on TV watching (Incidence rate ratio (IRR) = 0.89, 95% CI = [0.81-0.98]), internet use (IRR = 0.87, 95% CI = [0.79-0.96]), after-school sports (IRR = 0.91, 95% CI = [0.83-0.99]), and household chores (IRR = 0.85, 95% CI = [0.80-0.92]). Overweight/obesity risks for only-sons were particularly pronounced in urban China, where only-sons were 36% more likely to be overweight and 43% more likely to be obese than sibling-sons. Only-daughters had a higher risk of obesity (OR = 1.43, 95% CI = [1.01-2.04]) than sibling-daughters. However, the association was not significant for either urban girls or rural girls examined separately. Only-daughters in rural areas spent less time helping with household chores (IRR = 0.88, 95% CI = [0.80-0.97]) than sibling-daughters. CONCLUSIONS Future childhood obesity interventions should pay special attention targeting the large young only-child population in China.