Breastfeeding, socio-economic conditions and nutritional status of children younger than 12 months in Brazil.

Taking account of socio-economic determinants such as maternal education and family income, nutritional status and its relationship to breastfeeding and socio-economic conditions were studied in 419 children aged 3-12 months in the city of Niterói in south-eastern Brazil. Data were obtained by sampling a population during a high coverage (90%) vaccination campaign in 1992. After stratifying by maternal educational level, the relative risk (prevalence ratio) for height-for-age (H/A) Z-score < -1 in relation to no breastfeeding was 2.2 (95% CI 1.1-4.2) for families where mothers had been educated for less than 4 years and 0.7 (95% CI 0.4-1.1) otherwise, indicating a significant interaction (modifying effect) between breastfeeding and the control variable (chi 2 = 7.4; p = 0.006). Similar results were found when family income was used as the stratification variable (RR 2.2, 95% CI 1.1-4.3 in the lower and RR 0.7, 95% CI 0.4-1.2 in the higher income stratum; chi 2 = 6.7; p = 0.009). The population-attributable risk fraction indicated that in the age group analysed a reduction of about 40% in the number of children with HAZ < -1 could be achieved in low-income/low-education families by the widespread adoption of breastfeeding.