Analysis of the association between physical health and BMI in single-child and multiple-child families: a study based on the SUREG model and the BMA approach.

backgroundChina's single children policy, implemented from 1979 to 2015, lasted for 35 years, with the result that China is now the country with the highest number of children without siblings in the world. This policy profoundly reshaped China's family structure and parenting models, significantly impacting adolescents' physical health and Body Mass Index (BMI).

methodsThis study analyzes data from the Chinese Adolescent Health Database, comprising 7,482 adolescents aged 12-18 years from 17 cities in Shandong Province collected between 2015 and 2020. The database includes indicators such as height, weight, 50-meter sprint, standing long jump, sit-and-reach, and vital capacity, which were assesses these indicators against the revised National Student Physical Health Standards of 2014 (CNSPHS). Using the Seemingly Unrelated Regression (SUR) model and Bayesian Model Averaging (BMA), the study examines the specific effects of being a single child on physical fitness test scores (PFTS) and BMI, and the nonlinear relationship linking the two. Among the participants, 28% (n = 2,089) were only children and 72% (n = 5,393) had siblings. The primary purpose of this study is to quantify the impact of China's one-child policy on adolescent physical health outcomes through rigorous statistical analysis, providing evidence-based insights for targeted interventions to improve health outcomes in this unique demographic group.

resultsThe SUR regression indicated that the PFTS and BMI scores of single children were lower than those of multiple-child families' children by 1.412 and 1.213 points, respectively. Further analysis uncovered an inverted U-shaped relationship linking PFTS to BMI, indicating an optimal, moderate BMI range for physical health. These results highlight the importance of monitoring BMI in adolescent health management and underscore the necessity of targeted physical activities and nutritional guidance for single child.

conclusionBeing a single child has a significant negative impact on physical test scores and BMI, indicating potential vulnerabilities in their physical health. This discovery is crucial for policymakers and educators, prompting them to provide more opportunities for physical activity and to strengthen the cultivation of healthy eating habits among only children, thereby enhancing their physical health and overall well-being.