Time trends and factors in body mass index and obesity among children in China: 1997-2011.

BACKGROUND: Research on the shift in children's body mass index (BMI) distribution is limited and conditional mean models used in the previous research have limitations in capturing cross-distribution variations in effects. The objectives are to analyze the shift in Chinese children's BMI distribution and to test the associations between BMI distribution and other factors. METHODS: We analyzed data collected from children 7 to 17 years old from the China Health and Nutrition Survey (CHNS) conducted in 1997, 2000, 2004, 2006, 2009 and 2011, from 2814 participants with 6799 observations. Longitudinal quantile regression (QR) was used to explore the effect of several factors on BMI trends in 2015. RESULTS: The BMI curves shift to the right in boys and girls, with the distributions becoming wider, indicating a higher proportion of children have become overweight. The 5th, 15th, 50th, 85th and 95th BMI percentile curves all shifted upward from 1997 to 2011, and the higher percentiles had greater increases. The prevalence of overweight and obesity increased in boys and girls between 1997 and 2011, from 6.5 to 15.5% in boys and from 4.6 to 10.4% in girls. Energy intake and parents' BMI levels had a positive association with children's BMI. Per capita income was positively associated with changes in BMI only at the upper percentiles of the BMI distributions in boys. Increased physical activity (PA) was associated with decreased BMI in girls. CONCLUSIONS: Children in China are becoming increasingly overweight. Energy intake, parental BMI, PA and early menarche age in girls are associated with elevated BMI in children.