title: The influence of birth order and number of siblings on adolescent body composition: evidence from a Brazilian birth cohort study.
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.
authors.affiliation: Post-Graduate Program in Epidemiology, Federal University of Pelotas,Pelotas,Brazil.
authors.forename: Fernanda
authors.initials: F
authors.lastname: de Oliveira Meller
authors.affiliation: Post-Graduate Program in Epidemiology, Federal University of Pelotas,Pelotas,Brazil.
authors.forename: M C F
authors.initials: MC
authors.lastname: Assunção
authors.affiliation: Post-Graduate Program in Epidemiology, Federal University of Pelotas,Pelotas,Brazil.
authors.forename: A A
authors.initials: AA
authors.lastname: Schäfer
authors.affiliation: Post-Graduate Program in Epidemiology, Federal University of Pelotas,Pelotas,Brazil.
authors.forename: C L
authors.initials: CL
authors.lastname: de Mola
authors.affiliation: Post-Graduate Program in Epidemiology, Federal University of Pelotas,Pelotas,Brazil.
authors.forename: A J D
authors.initials: AJ
authors.lastname: Barros
authors.affiliation: Department of Epidemiology and Public Health,University College Cork,Cork,Republic of Ireland.
authors.forename: D L
authors.initials: DL
authors.lastname: Dahly
authors.affiliation: Post-Graduate Program in Epidemiology, Federal University of Pelotas,Pelotas,Brazil.
authors.forename: F C
authors.initials: FC
authors.lastname: Barros
mesh_terms: D000293:Adolescent; D000328:Adult; D001722:Birth Order; D001823:Body Composition; D015992:Body Mass Index; D001938:Brazil; D015331:Cohort Studies; D005191:Family Characteristics; D005260:Female; D006801:Humans; D008297:Male; D008423:Maternal Age; D009765:Obesity / Q000517:prevention & control; D011247:Pregnancy; D035781:Siblings
keywords: Adolescents; Birth order; Body composition; Cohort studies; Siblings