Gee, who could have seen this coming?
I, and others, have been pointing out for years that although the benefits of breastfeeding are real, they are small and restricted to relatively unimportant risks like colds or episodes of diarrheal illness during the first year of life. To hear lactivists tell it, however, breastmilk has super powers and women who do not breastfeed are bad mothers.
Now a new study, Is Breast Truly Best? Estimating the Effects of Breastfeeding on Long-term Child Health and Wellbeing in the United States Using Sibling Comparisons by Colen and Ramey, confirms what the scientific evidence has shown all along. The benefits of breastfeeding are trivial.
This, in many ways, is the study that we have been waiting for. We have always known that breastfeeding varies among ethnic, cultural and economic groups and indeed, previous studies that corrected for these factors show that breastfeeding has only small advantages. The new study looks at breastfeeding vs. bottlefeeding WITHIN families by comparing siblings who were fed differently.
The authors explain:
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.
The paper is 55 pages long and packed with charts, graphs and statistical analyses. The authors analyzed the impact of breastfeeding vs. bottlefeed in the whole group, between different families, and within the same family.
What did the authors find?
In Table 3, we present descriptive statistics by breastfeeding status (yes/no) for the eleven outcomes of interest across three different subgroups – the full NLSY-Children’s sample, the sibling sample, and the discordant sibling sample. Results for the first two subgroups are remarkably similar. Mean levels of BMI, hyperactivity, math skills, reading recognition, vocabulary word identification, digit recollection, and scholastic competence as well as the percentage of respondents who are obese all appear to significantly (p < 0.05) differ between children who were breastfed and those who were not and are in the predicted direction, with breastfed children exhibiting better outcomes. When the sample is restricted to discordant siblings, mean scores across all eleven indicators of child health and wellbeing are comparable and differences between breast- and bottle-fed respondents are small enough to be attributable to random chance alone.
Here is a modified version of Table 3:
I modified it to make it easier to read by color coding each group and by masking the number of individuals in each group. You can find the original chart here.
The authors explain:
Findings from the full sample (Model 1) suggest that children who were breastfed during the first year of life were significantly better off than their bottle-fed counterparts. Asthma was the only endpoint of interest that did not adhere to the expected patterning of results, in which breastfed children do better than their bottle-fed counterparts. Results from Model 2 demonstrate the consistency of our findings between the full and sibling subsamples. With the exception of one outcome (hyperactivity), regression coefficients remain remarkably similar between Models 1 and 2, standard errors increase only slightly, and the conclusions that can be drawn are virtually identical.
The most stringent test of the hypothesis that breastfeeding during infancy positively influences long-term childhood outcomes occurs when we include fixed effects for each NLSY79 mother, thus limiting comparisons to within rather than across families (Table 4, Model 3). What is most striking about these findings is the extent to which regression coefficients are attenuated, with a few even changing signs. Furthermore, none of the estimates maintain statistical significance (p < 0.05)...
In other words, there were difference between breastfed and bottle fed children in 10 of the 11 measured variables when looking at the overall group. Those differences persisted when comparing families in which all the children were breastfed to families where all the children were bottlefed. But when the authors looked within families, there was no significant difference between breastfed and bottle fed children.
Simply put, looking within families takes ethnic, cultural and socio-economic factors out of the picture. When you do that, you find no difference between breastfed and bottlefed children.
Colen and Ramey also looked at the impact of duration of breastfeeding and found the findings were the same:
…Findings from Model 1, which reflects the standard multiple regression approach, illustrate that each additional week of breastfeeding is associated with significant decreases in BMI, the odds of obesity, and hyperactivity as well as significant increases in parental attachment, math achievement, reading recognition, vocabulary identification, memory based intelligence (WISC), and scholastic competence. Results from Model 2, which is restricted to the sibling sample, are almost identical to those from Model 1, suggesting that selection into the sibling subgroup is not likely to bias our findings.
Finally, estimates from fixed effects regression models that limit comparisons to those occurring within, as opposed to between, families reveal a different story – one in which breastfeeding for longer periods of time does not necessarily result in better childhood health and wellbeing. When moving from Model 2 to Model 3, the coefficients for PIAT Math, PIAT Reading, PPVT, and scholastic competence decrease by 79%, 83%, 92%, and 88%, respectively. Moreover, the sign of the coefficient is not only reduced but actually changes direction for three additional outcomes (BMI, obesity, and WISC)…
Once again, it appears that breastfeeding improves a variety of health and educational outcomes, but when hold ethnic, cultural and socio-economic factors constant by looking only within families, the improvements not only vanish, but in some cases the breastfed children do poorly compared to their bottlefed siblings.
The authors summarize their findings:
Results from between-family comparisons suggest that both breastfeeding status and duration are associated with beneficial long-term child outcomes. This trend was evident for 10 out of the 11 outcomes examined here. When we more fully account for unobserved heterogeneity between children who are breastfed and those who are not, we are forced to reconsider the notion that breastfeeding unequivocally results in improved childhood health and wellbeing. In fact, our findings provide preliminary evidence to the contrary. When comparing results from between- to within-family estimates, coefficients for 10 of the 11 outcomes are substantially attenuated toward zero and none reach statistical significance (p < 0.05). Moreover, the signs of some of the regression coefficients actually change direction suggesting that, for some outcomes, breastfed children may actually be worse off than children who were not breastfed.
Colen and Ramey are mindful of the policy implications of their findings:
Efforts to increase breastfeeding that solely focus on individually based behavior change without addressing the economic and social realities women face and the difficult tradeoffs they are forced to make in the months following the birth of their child risk alienating and stigmatizing the very women they hope to help…
… A truly comprehensive approach to increasing breastfeeding in the U.S., with a particular focus on reducing racial and SES disparities, will need to work toward increasing and improving parental leave policies, flexible work schedules and health benefits even for low-wage workers, and access to high quality child care that can ease the transition back to work for both mother and child. Hopefully, this multifaceted approach will allow women who want to breastfeed to do so for as long as possible without promoting a cult of “total motherhood” in which women’s identities are solely constructed in terms of providing the best possible opportunities for their children and the risks associated with a failure to breastfeed are drastically overstated (Wolf, 2011).
Simply put, every mother should be able to breastfeed for as long she wants to do so, but there is no reason to make women feel guilty if they don’t want to breastfeed or don’t want to breastfeed for long. The benefits of breastfeeding have been dramatically overstated and it is time to correct our advice to mothers to reflect the real benefits of breastfeeding, not the imagined super powers that simply don’t exist.