Sibship Composition and BMI Z-Score Among Saudi Preschoolers: A Cross-Sectional Study

Background and objective The association between sibship composition and child body mass index (BMI) has not been investigated in any Arab/Middle Eastern populations. In light of this, this study aimed to examine the association of the number of siblings, number of older siblings, and number of younger siblings with child BMI z-score (BMIz) among preschoolers in the Kingdom of Saudi Arabia (KSA). Methods A total of 209 mothers and their children were recruited from preschools in Jeddah, KSA. Mothers reported their responses to the study questionnaire via telephone. Child anthropometry was objectively measured; BMIz was calculated based on age- and sex-specific World Health Organization (WHO) growth standards and reference data. We used hierarchical multiple linear regression to examine the association between sibship composition variables and child BMIz, independent of the effect of potential confounders, and to evaluate changes in model fit. Results The number of siblings was negatively associated with child BMIz [b = -0.18, 95% confidence interval (CI) = -0.35, -0.06, p<0.01, adjusted R² = 0.16]. There was a negative association between the number of older siblings and child BMIz (b = -0.23, 95% CI = -0.38, -0.11, p<0.01, adjusted R² = 0.21) as well as between the number of older sisters and child BMIz (b = -0.18, 95% CI = -0.52, -0.09, p<0.01, adjusted R² = 0.19). However, there were no significant associations between the number of older brothers or the number of younger siblings and child BMIz. Conclusions Based on our findings, sibship composition was found to be associated with BMIz among a sample of preschoolers in KSA. More research is needed to further establish this association and to understand the underlying mechanism of the association of the greater number of older siblings and older sisters with lower BMIz.