Journal of Paediatrics and Child Health (2001) 37 (5): 465-469. doi:10.1046/j.1440-1754.2001.00702.x The Effect Of Breastfeeding On Child Development At 5 Years: A Cohort Study PJ QUINN, 1 M O’CALLAGHAN, 2 GM WILLIAMS, 3 JM NAJMAN, 4 MJ ANDERSEN 5 and W BOR 6 1 Mater Children’s Hospital 2 Child Development and Rehabilitation Services, Mater Children’s Hospital, 3 Tropical Health and Nutrition Program, University of Queensland 4 Department of Anthropology and Sociology,University of Queensland 5 Department of Obstetrics and Gynaecology, University of Queensland 6 Child and Youth Mental Health, Royal Children’s Hospital Health District, Brisbane, Queensland, Australia Abstract Objective: It is uncertain to what degree the relationship between breastfeeding and later cognitive development is a true biological effect, or is confounded by psychosocial factors. The study aim was to further investigate this relationship and the effect of duration of breast feeding on cognitive development. Methods: A total of 3880 children were followed from birth. Breastfeeding duration was measured by questionaire at 6 months of age and a Peabody Picture Vocabulary Test Revised (PPVT-R) was administered at 5 years. PPVT-R scores were adjusted for the effects of a large array of biological and psychosocial confounders. The relationship between breastfeeding and the mean PPVT-R scores were examined using analysis of variance and multiple linear regression. Results: A strong positive relationship was demonstrated between breastfeeding and the PPVT-R scores with increasing scores with increased duration of breastfeeding. After adjusting for a wide range of biological and social factors, the adjusted mean for those breastfed for 6 months or more was 8.2 points higher for females and 5.8 points for males when compared to those never breastfed. Conclusion: These findings suggest a significant benefit to child development is conferred by breastfeeding and is related independently to longer periods of breastfeeding. Keywords: breastfeeding; child development; intelligence; Peabody; cohort studies A substantial body of evidence suggests a benefit on cognitive development in infants as a result of breastfeeding. [1–7] Several population studies have been conducted in term infants, the majority of which show a positive effect on cognitive development in breastfed infants. [2–5] This positive association is by no means universal or necessarily indicative of a causal association. Several studies have shown that a large number of social and parental educational factors that could reasonably be expected to influence child development independently effect the incidence of breastfeeding. [2–4] Studies by Silva et al. [8] Jacobson et al.,[9] and Wigg et al.[10] suggest that once con-founders such as social advantage, maternal education and intelligence, and the quality of a child’s developmental experiences were taken into account, the differences between bottle and breastfed groups were no longer statistically significant. A number of criticisms including lack of statistical power,[8] populations initially selected for other exposures [9,10] and the timing and quality of measurement of intervening variables [9] can be made of these studies. Pollock [4] selected a cohort of relatively advantaged mothers, and after controlling for factors associated with the likelihood of breastfeeding, demonstrated that infants breastfed for at least 3 months had small though statistically significant improvements in mean picture vocabulary scores at 5 years and ability scores at 10 years. If the association between breastfeeding and infant cognitive development is causal, two possible explanations have been suggested. First, a unique nutritional component of breast milk, possibly a lipid, could be essential for optimal brain development. The most often discussed is the Omega-3 fatty