Association between breastfeeding and body mass index at age 6-7 years in an international survey.

Background: Breastfeeding is believed to reduce children's risk for obesity but data are conflicting. It is also uncertain if breastfeeding has different effects on obesity in high- and low-income countries.

Objectives: This study aimed to investigate the association between having been breastfed and body mass index (BMI) in 6- to 7-year-old children in a large international survey.

Methods: Parents/guardians reported whether their child had been breastfed and their current height and weight. Some centres measured height and weight directly. Analyses adjusted for whether height and weight were reported or measured, child's age, sex, country gross national income and centre.

Results: Data were available for 76,635 participants from 31 centres in 18 countries. Reported breastfeeding rates varied from 27 to 98%. After adjusting for potential confounders, the estimated BMI difference was 0.04 kg m(-2) lower among those who had been breastfed (P = 0.07). The risk for being overweight or obese was slightly lower among breastfed children (odds ratio = 0.95, P = 0.012). There was no evidence that the association between breastfeeding and BMI was different in lower income countries compared with higher income countries.

Conclusions: The findings suggest that breastfeeding has little impact on children's BMI. Increasing breastfeeding is unlikely to reduce the global epidemic of childhood obesity.