The long-run returns to breastfeeding
Marco Francesconi, Stephanie von Hinke, Emil N. Sørensen
TL;DR
This study investigates the long-run health and human capital returns to maternal breastfeeding in the UK using a historical context where breastfeeding fell from over 80% to around 40% between the 1930s and 1970s. It combines a within-family (sibling) design with genetic data, including outcome-specific polygenic indices ($PGI$) and gene–environment interaction tests ($G\times E$). The main findings show modest but persistent advantages for those breastfed in adulthood—smaller height increases and faster gains in fluid intelligence—with within-family estimates mitigating confounding; BMI and educational attainment appear largely driven by family factors, with little evidence of $G\times E$ moderation except a possible height-specific effect. These results highlight a non-negligible role for early-life breastfeeding in child development and demonstrate the utility of combining sibling comparisons with genetic data to parse direct and interaction effects, while also noting limitations due to recall-based measures and historical context.
Abstract
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.