Effects of birth weight on body composition and overweight/obesity at early school age

Objectives: The prevalence of childhood obesity has increased substantially. We aimed to characterize the effect of birth weight on body composition and overweight/obesity at early school age. Study design: A total of 1669 children with available birth records from a double-blind cluster-randomized controlled trial exploring micronutrient supplementation during pregnancy were included. Data regarding school-aged body composition, social-demographic factors and health behaviours were prospectively collected. Result: s: The study population consisted of 1004 boys and 665 girls aged between 7 and 10 years. The prevalence of overweight/obesity (>85th age-sex-specific percentiles) was 7.4% for boys and 5.0% for girls. Generalized estimating equation models were used to account for the cluster nature of the data. A significant upward trend across quintiles of birth weight was observed for fat mass index (boys: P for trend 0.002; girls: P for trend <0.001), fat-free mass index (boys: P for trend <0.001; girls: P for trend <0.001), and percentage of body fat (boys: P for trend 0.003; girls: P for trend <0.001). A birth weight in the higher three quintiles could increase the risk ratios [RRs (95% CI) third quintile: 2.88, (1.13, 7.32); fourth quintile: 2.40, (0.87, 6.66); top quintile: 2.31, (0.92, 5.80)] of overweight/obesity at early school age compared with the RRs of the reference group (the second quintile of birth weight) among boys. Conclusions: Higher birth weight could increase the risk of being overweight/obese among 7- to 10-year-old boys in rural western China. Sex differences in this association need to be considered when planning interventions. Research registration: This trial was registered at www.isrctn.com with the identifier ISRCTN08850194.