Long-term trends and urban-rural disparities in the physical growth of children and adolescents in China: an analysis of five national school over three decades

Background China's rapid economic growth has brought opportunities for improved health and growth of children and adolescents. We sought to explore the long-term trends and urban-rural inequalities in physical growth (specifically height and BMI) among school-aged children and adolescents in China to identify policy priorities for a healthier generation. Methods We used the 1985, 1995, 2005, 2014, and 2019 cycles of the Chinese National Survey on Students' Constitution and Health from primary and secondary schools in 30 mainland provinces, autonomous regions, and municipalities. We analysed height and BMI data for 7, 12, and 18 year old children and adolescents of Han ethnicity. Children and adolescents who had complete data on age, sex, location, weight, and height were included. All surveys used a multi-stage stratified random cluster sampling method and were nationally representative. A univariate kernel density estimation was used to plot the distribution of height and BMI. Quantile regression was used to examine associations between urban and rural locations and the primary outcomes of height and BMI at specific quantiles of distribution (5th, 25th, 50th, 75th, and 95th). Findings Across the five surveys (in 1985, 1995, 2005, 2014, and 2019), 313 973 children and adolescents were included. From 1985 to 2019, the height and BMI distribution curves shifted to the right for each age group and sex, with the BMI curve becoming more dispersed. Median height in adolescents aged 18 years increased by 3 center dot 8 cm (95% CI 3 center dot 4-4 center dot 1) in boys in urban areas and 5 center dot 7 cm (5 center dot 3-6 center dot 1) in boys in rural areas, and 2 center dot 7 cm (2 center dot 4-3 center dot 0) in girls in urban areas and 3 center dot 7 cm (3 center dot 4-4 center dot 0) in girls in rural areas. Children in urban areas were taller than those in rural areas at every quantile, but the magnitude of this disparity narrowed by 2019. In 2019, the median height of boys in urban areas were 1 center dot 4 cm (1 center dot 0-1 center dot 8) greater in those aged 7 years, 2 center dot 5 cm (1 center dot 9-3 center dot 1) greater in those aged 12 years, and 1 center dot 1 cm (0 center dot 6-1 center dot 5) greater in those aged 18 years than their rural counterparts, whereas the median height of girls in urban areas were 1 center dot 1 cm (0 center dot 7-1 center dot 4) greater in those aged 7 years, 1 center dot 6 cm (1 center dot 1-2 center dot 1) greater in those aged 12 years, and 1 center dot 1 cm (0 center dot 7-1 center dot 5) greater in those aged 18 years than rural girls. Over this period, urban-rural differences in BMI disappeared at the lowest quantile, but persisted at higher quantiles. In 2019, the urban-rural differences in BMI for boys aged 12 years were 0 center dot 6 kg/m2 (95% CI 0 center dot 3-0 center dot 8) at the median, 1 center dot 0 kg/m2 (0 center dot 6-1 center dot 4) at the 75th quantile, and 0 center dot 7 kg/m2 (0 center dot 1-1 center dot 3) at the 95th quantile; for girls aged 12 years, 0 center dot 3 kg/m2 (0 center dot 1-0 center dot 5) at the median, 0 center dot 5 kg/m2 (0 center dot 2-0 center dot 8) at the 75th quantile, and 0 center dot 9 kg/m2 (0 center dot 3-1 center dot 5) at the 95th quantile; for boys aged 18 years, 0 center dot 6 kg/m2 (0 center dot 4-0 center dot 8) at the median, 0 center dot 8 kg/m2 (0 center dot 5-1 center dot 2) at the 75th quantile, and 0.7 kg/m2 (0 center dot 0-1 center dot 5) at the 95th quantile; and for girls aged 18 years, 0 center dot 2 kg/m2 (0 center dot 1-0 center dot 4) at the median, 0 center dot 5 kg/m2 (0 center dot 3-0 center dot 8) at the 75th quantile, and 1 center dot 0 kg/m2 (0 center dot 5-1 center dot 5) at the 95th quantile. Interpretation Across three decades, school-aged children and adolescents in China have increased in height and BMI, with less disparity between urban and rural locations. Investments are needed to improve the affordability of healthy foods to help children and adolescents in rural areas reach their potential maximum height. Meanwhile, these changes in BMI necessitate tailored strategies according to urban-rural settings to contain the increase in overweight and obesity and promote optimal growth for children and adolescents.