Are single children more likely to be overweight or obese than those with siblings? The influence of China's one-child policy on childhood obesity

China's one-child policy (1979-2015) has affected Chinese parenting practices and children's health behaviors and also may have contributed to increased childhood obesity. However, very limited research has investigated the association between one-child policy and childhood obesity. We examined characteristics of single-child families and the influence of one-child policy (indicated by single-child status) on children's weight status and related health behaviors. Data from children aged 6-18years old in the 2011 (n=1580) and 2000 (n=2317) China Health and Nutrition Survey were cross-sectionally analyzed with multilevel models. From 2000 to 2011, the rates about doubled for being a single-child (30.1% to 57.0%) and being overweight or obese (OWB, 6.6% to 16.5%) along with urbanization (27.5% to 37.1%). Single-child families had higher levels of parental education, household income and urban residence than families with ≥ two children (p<0.05). Compared to the children with siblings, single children were more likely to be OWB; the association became stronger over time (OR=4.5 (1.7-12.4) in 2011 and 1.7 (1.0-2.8) in 2000). Also, single children had less recreational screen time, but similar physical activity levels; however single urban children were more likely to have excess total energy intake (OR=5.70 (1.58-20.60)) than those with siblings. Being single-child is about four times more likely to be overweight/obesity than those having siblings, and the association became stronger over time in China. China's one-child policy might have contributed to its rising childhood obesity rates. Obesity intervention programs may need to account for the influence of the one-child policy in China.