Gender and social mobility modify the effect of birth weight on total and central obesity
OBJECTIVE Little is known about the contribution of childhood socio-economic position (SEP) and social mobility to weight change. The present study evaluated the effect of family SEP during the pre-school years and social mobility on BMI between birth and adolescence. DESIGN Longitudinal. The SEP of each child's family was classified according to an asset-based wealth index as low, medium or high. Four different categories of childhood-adolescence SEP groups were created in order to examine social mobility: low-medium/high, medium-medium, medium-high and high-high/medium. For each of these categories, BMI was tracked from birth to adolescence. Linear mixed-effects models were used to analyse the data. SETTING Cuiabá-MT, Brazil. SUBJECTS A population-based cohort of children born between 1994 and 1999 was assessed between 1999 and 2000, and again between 2009 and 2011. RESULTS A total of 1716 adolescents were followed from childhood to adolescence (71·4 % of baseline). The prevalence of overweight/obesity was 20·4 % in childhood and 27·7 % in adolescence. A higher SEP in childhood was associated with a greater prevalence of overweight in adolescence. Expressive upward social mobility occurred, mainly in the lowest SEP group. There was a greater rate of change in BMI between birth and adolescence among children with a higher SEP in childhood and children who remained in the higher SEP from childhood to adolescence. CONCLUSION Individuals from a higher SEP in childhood and those who remained in the higher social classes showed greater rate of change in BMI. Thus, initial SEP was the major determinant of changes in BMI.