Association of family income with BMI from childhood to adult life: a birth cohort study

OBJECTIVE: To investigate the association of family income at birth with BMI among young adults who have been followed since birth. DESIGN: A birth cohort study. SETTING: In 1982, all children born in Pelotas, southern Brazil, were included in a perinatal survey and visited at ages 1, 2, 4, 15, 18–19 and 23 years. SUBJECTS: Cohort members (n 4297) were traced and interviewed in 2004–2005. In all follow-ups, participants were weighed and measured, and BMI and prevalence of obesity were calculated for each age. Family income was obtained in minimum wages in 1982 and as a continuous variable, in reais, in later follow-ups. Skin colour was self-reported in 2004–2005. RESULTS: Mean BMI and prevalence of obesity differed between males and females. In males, a direct relationship was found throughout life and among females this relationship was modified by age. During childhood, BMI was higher among girls from higher income groups and this association was inversed at age 23 years. At this same age, mean BMI among black women was 1·3 kg/m(2) higher than among white women, even after adjustment for current family income. CONCLUSIONS: The findings show in men that the relationship between income and BMI is similar to that seen in less developed areas, whereas among adult women the relationship is similar to that observed in developed countries. In addition to the effect of socio-economic status, skin colour also has an influence on the BMI of adult women.