Abstract
The aim of this study was to estimate the association between birth order and number of siblings with body composition in adolescents. Data are from a birth cohort study conducted in Pelotas, Brazil. At the age of 18 years, 4563 adolescents were located, of whom 4106 were interviewed (follow-up rate 81.3 %). Of these, 3974 had complete data and were thus included in our analysis. The variables used in the analysis were measured during the perinatal period, or at 11, 15 and/or 18 years of age. Body composition at 18 years was collected by air displacement plethysmography (BOD POD®). Crude and adjusted analyses of the association between birth order and number of siblings with body composition were performed using linear regression. All analyses were stratified by the adolescent sex. The means of BMI, fat mass index and fat-free mass index among adolescents were 23.4 (sd 4.5) kg/m², 6.1 (sd 3.9) kg/m² and 17.3 (sd 2.5) kg/m², respectively. In adjusted models, the total siblings remained inversely associated with fat mass index (β = - 0.37 z-scores, 95 % CI - 0.52, - 0.23) and BMI in boys (β = - 0.39 z-scores, 95 % CI - 0.55, - 0.22). Fat-free mass index was related to the total siblings in girls (β = 0.06 z-scores, 95 % CI - 0.04, 0.17). This research has found that number of total siblings, and not birth order, is related to the fat mass index, fat-free mass index and BMI in adolescents. It suggests the need for early prevention of obesity or fat mass accumulation in only children.
Highlights
The aim of this study was to estimate the association between birth order and number of siblings with body composition in adolescents
The influence of birth order on the occurrence of obesity has been investigated, but the findings are inconsistent in previous studies
Data are from a population-based birth cohort study located in Pelotas, Brazil
Summary
The aim of this study was to estimate the association between birth order and number of siblings with body composition in adolescents. Studies have shown that a larger number of siblings is associated with lower prevalence of obesity in adolescence[3,4], regardless of whether siblings are younger or older[4] There are both social and biological explanations of how birth order and/or number of siblings might influence adolescent body composition. It is critically important to better understand the relative importance of both birth order and number of siblings, a challenge few previous studies have addressed To help fill this gap, we used data from the 1993 Birth Cohort of Pelotas, Brazil, which included detailed information on family structure, to evaluate the association between both birth order and number of siblings with body composition in 18-year-old adolescents
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