Is breast truly best? Estimating the effects of breastfeeding on long-term child health and wellbeing in the United States using sibling comparisons

Abstract

Breastfeeding rates in the U.S. are socially patterned. Previous research has documented startling racial and socioeconomic disparities in infant feeding practices. However, much of the empirical evidence regarding the effects of breastfeeding on long-term child health and wellbeing does not adequately address the high degree of selection into breastfeeding. To address this important shortcoming, we employ sibling comparisons in conjunction with 25 years of panel data from the National Longitudinal Survey of Youth (NLSY) to approximate a natural experiment and more accurately estimate what a particular child’s outcome would be if he/she had been differently fed during infancy. Results from standard multiple regression models suggest that children aged 4 to 14 who were breast- as opposed to bottle-fed did significantly better on 10 of the 11 outcomes studied. Once we restrict analyses to siblings and incorporate within-family fixed effects, estimates of the association between breastfeeding and all but one indicator of child health and wellbeing dramatically decrease and fail to maintain statistical significance. Our results suggest that much of the beneficial long-term effects typically attributed to breastfeeding, per se, may primarily be due to selection pressures into infant feeding practices along key demographic characteristics such as race and socioeconomic status.

Widespread covariation of early environmental exposures and trait-associated polygenic variation

“…This includes both parenting characteristics and broad socioeconomic variables; all are partially heritable (23)(24)(25)(26)(27)(28). In the past decade, quantitative genetic research of this type has been extended to explore genetic and environmental contributions to correlations between environmental factors and children's outcomes (29)(30)(31)(32). Some new designs such as the children-of-twins designs make it possible to tease apart different types of genotype-environment correlation and identify environmental influences free of genetic confounds (33)(34)(35)(36)(37).…”

Using the National Longitudinal Surveys of Youth (NLSY) to Conduct Life Course Analyses

“…Some of these include how income and family structure impact routine medical and dental care provision for children (Berger 2004), the association between unwanted pregnancy and prenatal and postpartum maternal behaviors that adversely affect infant and child health (Joyce et al 2000), the relationship between dark and cluttered home environments and the incidence of home injuries among children (Mott 1999), the distance between a child's home and a hospital and the probability of utilizing preventive care (Currie and Reagan 2003), length of maternity leave and children's immunizations (Berger et al 2005), the effects of breastfeeding on long-term child health and well-being (Colen and Ramey 2014), various measures of economic disadvantage on intrauterine growth restriction ), household income histories, and changes in child depression levels (Strohschein 2005). Finally, a recent paper by Wolfe (2015) unpacked the components of socioeconomic status and found that children's health was more vulnerable to their families' wealth whereas adolescents' health was more sensitive to the current income of their families.…”

Effects of Breastfeeding on Obesity and Intelligence

“…This result is consistent with the RCT, sibling-pair, and cross-population studies, which all suggest there is no effect of breastfeeding on mea-sures of obesity. 4,5,8 Most cohort studies of breastfeeding and obesity (largely from rich countries) may reproduce the same patterns of residual and unmeasured confounding. This is apparent when the RCT data were analyzed ignoring the randomized treatment assignment: no effect of the breastfeeding promotion intervention on infant growth in the RCT, but effects observed when the RCT was analyzed observationally (ie, as fed, rather than as randomized).…”

“…5 However, sibling-pair comparisons show a much smaller effect of 0.22 higher (SE, 0.18) IQ scores comparing breastfed and not breastfed siblings. 8 Thus, the RCT, cohort, and crosspopulation studies suggest that breastfeeding raises IQ, but negligible effects are noted in sibling studies. Methods for evaluating health evidence give greater weight to RCTs.…”