Breast is best, but for how long? Testing breastfeeding guidelines for optimal cognitive ability

Objectives: To investigate the relationship between breastfeeding duration and cognitive
development using longitudinal survey data. The World Health Organisation (WHO) and the
American Academy of Pediatrics (AAP) recommend exclusive breastfeeding until six months post-partum and a combination of complementary foods and breast milk thereafter. This study estimates non-parametric regression models to test whether these recommendations also hold
for cognitive ability.
Design: Longitudinal cohort study with two waves of 18,819 children who were born in the UK between 2000-2002. We estimate several generalised additive regression models to examine the impact of exclusive and non-exclusive breastfeeding duration on cognitive ability, while controlling for a range of confounding family characteristics.
Setting and Participants: Participants of the UK Millennium Cohort Study (MCS).
Main outcome measures: Cognitive development at age three as measured by the Bracken School Readiness Assessment.
Results: The models identify a non-linear relationship between exclusive and non-exclusive breastfeeding and cognitive ability. There are high initial positive returns to exclusive breastfeeding which peak at six months, with the returns to non-exclusive breastfeeding continuing to increase until 10/12 months. These results suggest that the WHO/AAP guidelines recommending exclusive breastfeeding for the first 6 months of life also hold for optimal cognitive ability. The models also show that the optimal switching point from exclusive to nonexclusive breastfeeding occurs at six months, and that a combination of breast milk and solids should continue until thereafter, peaking at 10 months.
Conclusion: While breastfeeding recommendations primarily target physical growth and development, our study confirms that such recommendations are also optimal for cognitive development. These results provide further evidence that recent UK policy initiatives to extend paid maternity leave is appropriate for the maximal development of the child’s cognitive
ability. While this study controls for a range of confounding factors, there may still exist unobserved family characteristics which mediate this relationship.