The long-run returns to breastfeeding

This paper shows that the mid-20th century was characterised by a considerable reduction in breastfeeding rates, reducing from over 80% in the late 1930s to just over 40% only three decades later. We investigate how maternal breastfeeding during this period has shaped offspring health and human capital outcomes in the UK. We use a within-family design, comparing children who were breastfed to their sibling(s) who were not. Our results show that breastfeeding increases adult height, as well as fluid intelligence, but does not affect educational attainment, nor adult BMI. In further analyses, we examine whether and how this impact varies with individuals' genetic "predisposition" for these outcomes, proxied by the outcome-specific polygenic index. We find that the "height-returns" to breastfeeding are larger among those genetically predisposed to be taller, with no genetic heterogeneity for the other outcomes, though we note that power in the within-family GxE analysis is more limited. Overall, our estimates suggest that breastfeeding plays a non-negligible role in child development.