Association of number of siblings, birth order, and thinness in 3- to 12-year-old children: a population-based cross-sectional study in Shanghai, China

Abstract

Background: To evaluate the associations among number of siblings, birth order, and childhood thinness as well as the effect of number of younger or older siblings on childhood thinness. Methods: In this study, we performed a population-based cross-sectional study among 84075 3- to 12-year-old children in Shanghai using multistage stratified cluster random sampling. We defined grade 1, 2, and 3 thinness according to the body mass index cutoff points set by the International Obesity Task Force, and used multivariable logistic regression models to estimate the odds ratio (OR) and 95% confidence interval (95% CI). Results: Compared with only children, sibling children were more likely to be thin: one sibling (OR = 1.21, 95% CI 1.11, 1.31) and two or more siblings (OR = 1.10 95% CI 1.02, 1.19); Middle children (OR = 1.14, 95% CI 1.04, 1.26) and youngest children (OR = 1.38, 95% CI 1.23, 1.55) had significantly increased ORs for childhood thinness. There was no statistically significant relationship, however, between a larger number of younger or older siblings and childhood thinness. Conclusions: Having either siblings or a higher birth order was positively associated with childhood thinness. The present study suggests that future interventions to prevent childhood thinness should consider family background as an important factor, especially in multi-child families.