Exclusive and Any Breastfeeding, Infant Formula Feeding, and Childhood Growth

OBJECTIVES To understand the association between exclusive breastfeeding, any breastfeeding, and infant formula feeding and childhood growth. METHODS A longitudinal cohort study was conducted among children from birth up to 10 years in Toronto, Canada. The primary exposure was exclusive breastfeeding. Secondary exposures were any breastfeeding and infant formula feeding. The primary outcome was body mass index z-score (zBMI). The secondary outcome was overweight and obesity (zBMI > 1). RESULTS In total, 5379 children were included and followed to 3 years of age on average. Each 1-month increase in exclusive breastfeeding was associated with 0.01 lower zBMI (95% CI, −0.02 to −0.00) and lower odds of overweight and obesity (OR, 0.96; 95% CI, 0.94–0.98) with similar associations for any breastfeeding (zBMI, −0.01; 95% CI, −0.01 to −0.00; OR, 0.98; 95% CI, 0.97–0.99). Each 1-month increase in infant formula feeding was associated with 0.01 higher zBMI (95% CI, 0.00–0.01) and higher odds of overweight and obesity (OR, 1.02; 95% CI, 1.01–1.03). There was little evidence for modifying effects between infant feeding practices. Infant formula feeding for 24 months was associated with 0.27 higher zBMI (95% CI, 0.14–0.41) and 72% higher odds (OR, 1.72; 95% CI, 1.22–2.44) of overweight and obesity when compared to exclusive breastfeeding to 6 months of age and any breastfeeding to 24 months of age. CONCLUSIONS Longer exclusive breastfeeding and any breastfeeding were associated with lower zBMI and lower odds of overweight and obesity, whereas the opposite was true for infant formula feeding. Effective breastfeeding interventions include postnatal, intensive, and in-person support provided by trained health care professionals.