Social inequalities in BMI trajectories: 8-year follow-up of the Pró-Saúde study in Rio de Janeiro, Brazil

Objective In a cohort of government employees in Rio de Janeiro, Brazil, we investigated prospectively, sex-specific associations between education and BMI trajectories and their potential effect modification by race. Design Of the 4030 participants in Phase 1 (1999), 3253 (81 %) participated in Phase 2 (2003) and 3058 (76 %) participated in Phase 3 (2006). Education was categorized as elementary, high school or college graduate. Study participants self-identified as White, Black or Pardo. BMI was calculated from measured weight and height. BMI trajectories were modelled using a generalized additive regression model with mixed effects (GAMM). Setting The Pro-Saúde Study, a longitudinal investigation of social determinants of health. Subjects Women (n 1441) and men (n 1127) who participated in the three phases of data collection and had complete information for all study variables. Results Women and men with less than high school, or only a high school education, gained approximately 1 kg/m² more than college graduates (women: 1·06 kg/m² (P<0·001) and 1·06 kg/m² (P<0·001), respectively; men: 1·04 kg/m² (P=0·013) and 1·01 kg/m² (P=0·277), respectively). For women only, race was independently associated with weight gain. Women identifying as Pardo or Black gained 1·03 kg/m² (P=0·01) and 1·02 kg/m² (P=0·10), respectively, more than Whites. No effect modification by race was observed for either men or women. Conclusions While both lower education and darker race were associated with greater weight gain, gender similarities and differences were observed in these associations. The relationship between weight gain and different indicators of social status are therefore complex and require careful consideration when addressing the obesity epidemic.