The slogan “Breast is Best” has been popularized by medical organizations and parenting networks to extoll the benefits of breastfeeding, yet the causal effects are widely debated. Our study contributes to the debate by examining whether breastfeeding has differential effects based on the propensity to breastfeed, which is also known as causal effect heterogeneity. Prior studies attempt to isolate the causal effect of breastfeeding by netting out confounding characteristics, but we argue that the effects of breastmilk are unlikely to operate in a vacuum. The social forces that promote or constrain breastfeeding among different populations in American society can also shape its effects. Using rich intergenerational panel data from the NLSY79 Child and Young Adult cohort (n = 7902), we evaluate heterogeneous treatment effects in the relationship between breastfeeding and child development from ages 4 to 14 using stratification-multilevel propensity score models. We find that breastfeeding is associated with small benefits for behavioral development, math scores, and academic ability among those with the highest propensities to breastfeed. By contrast, its small benefits for reading comprehension and vocabulary are concentrated among children with the lowest propensities to breastfeed. Our findings suggest that the social process of selection into breastfeeding cannot be fully disentangled from its estimated effects. The social context not only shapes who breastfeeds in American society, but also who benefits most.

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最适合谁？母乳喂养对儿童发育的异质性治疗效果

“母乳是最好的”口号已被医疗组织和育儿网络推广，以颂扬母乳喂养的好处，但其因果关系却广受争议。我们的研究通过检查母乳喂养是否具有基于母乳喂养倾向的不同影响（也称为因果效应异质性）来促进辩论。先前的研究试图通过消除混杂特征来分离母乳喂养的因果效应，但我们认为母乳的影响不太可能在真空中发挥作用。在美国社会不同人群中促进或限制母乳喂养的社会力量也可以影响其影响。使用来自 NLSY79 儿童和青年队列 (n = 7902) 的丰富的代际面板数据，我们使用分层多层次倾向评分模型评估母乳喂养与 4 至 14 岁儿童发育之间关系的异质治疗效果。我们发现，母乳喂养对那些最有母乳喂养倾向的人的行为发展、数学成绩和学术能力的好处很小。相比之下，它对阅读理解和词汇量的小好处集中在母乳喂养倾向最低的儿童身上。我们的研究结果表明，选择母乳喂养的社会过程不能完全脱离其估计的影响。社会背景不仅塑造了美国社会中谁进行母乳喂养，也塑造了谁受益最大。我们发现，母乳喂养对那些最有母乳喂养倾向的人的行为发展、数学成绩和学术能力的好处很小。相比之下，它对阅读理解和词汇量的小好处集中在母乳喂养倾向最低的儿童身上。我们的研究结果表明，选择母乳喂养的社会过程不能完全脱离其估计的影响。社会背景不仅塑造了美国社会中谁进行母乳喂养，也塑造了谁受益最大。我们发现，母乳喂养对那些最有母乳喂养倾向的人的行为发展、数学成绩和学术能力的好处很小。相比之下，它对阅读理解和词汇量的小好处集中在母乳喂养倾向最低的儿童身上。我们的研究结果表明，选择母乳喂养的社会过程不能完全脱离其估计的影响。社会背景不仅塑造了美国社会中谁进行母乳喂养，也塑造了谁受益最大。它对阅读理解和词汇量的微小好处集中在母乳喂养倾向最低的儿童中。我们的研究结果表明，选择母乳喂养的社会过程不能完全脱离其估计的影响。社会背景不仅塑造了美国社会中谁进行母乳喂养，也塑造了谁受益最大。它对阅读理解和词汇量的微小好处集中在母乳喂养倾向最低的儿童中。我们的研究结果表明，选择母乳喂养的社会过程不能完全脱离其估计的影响。社会背景不仅塑造了美国社会中谁进行母乳喂养，也塑造了谁受益最大。