Is breast best? Yes, but it’s really not much better than formula in the United States. The better you account for confounding factors, the more benefits of breastfeeding disappear.
Six years ago I wrote about the evidence for breastfeeding. I questioned an article that claimed 900 babies’ lives could be saved every year in the US if 90% of mothers breastfed for at least 6 months. I didn’t think that was true, but I did think the evidence supported the claim that breastfeeding was clearly better for babies. Now I’m not so sure we can trust that evidence.
A new study reevaluated the evidence from previous studies and found that the studies hadn’t adequately ruled out significant confounders. There are social, cultural and economic factors that contribute to the choice to breastfeed, factors that may have skewed the results of those studies to favor breastfeeding. The new study tried to correct for these issues.
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.
Breastfeeding rates are socially patterned in the US
- Race: 75% of White infants and 59% of Black infants were ever breastfed; and the rates of continued breastfeeding at 6 months were 47% vs. 30%.
- Family income: 74% breastfeeding for incomes above 185% of the federal poverty level; 57% for incomes below that
- Education: mothers who completed some high school, were high school graduates, or attended some college were 64%, 60%, and 39% less likely to breastfeed than mothers who graduated from college.
Sibling comparisons
They used data from the National Longitudinal Study of Youth to find discordant sibling pairs where one sibling was breastfed and the other was not. They looked at three measures of physical health (BMI, obesity, and asthma), three behavioral indicators (hyperactivity, parental attachment, and behavioral compliance), and five outcomes designed to predict academic achievement. They looked at a large number of maternal variables including age, race, marital status, educational attainment, income, employment, insurance, smoking, alcohol, and prenatal care. They used sophisticated statistical analyses to compare the impact of and account for these factors.
They found that the benefits of breastfeeding were not statistically significant and that for some outcomes, breastfed children may actually be worse off than children who were not breastfed. They say:
This study provides evidence that the link between breastfeeding and childhood health and wellbeing may not be as robust as originally thought; however, the conclusions drawn should be considered in the context of its limitations.
And they list and discuss several limitations of their study.
Other considerations
This study looked at long-term outcomes for children. It did not look at short-term outcomes or at the effects on maternal health. But it would seem logical that those outcomes would be similarly affected by socioeconomic confounders. This is enough to make us question previous breastfeeding studies that did not control for those confounders or use discordant sibling comparisons, and it points the way to better research in the future.
Breastfeeding entails sacrifices. It impacts jobs, working hours, and family income. Some women are physically unable to breastfeed, and others find it impossible or impractical for other reasons. If there were a strong benefit to the health of children, society should do everything possible to facilitate and encourage breastfeeding. But if the benefit is minimal or questionable, it is wrong to overstate the evidence and make women who don’t breastfeed feel guilty for endangering their child’s health. Bottle-feeding results in healthy babies too.
A recent episode of “Call the Midwife” (Season 5, Episode 2) on PBS highlighted this issue. A midwife nun had led a new mother to believe that she absolutely had to breastfeed for her baby to be healthy. Breastfeeding was unsuccessful and the baby nearly died of dehydration. Fiction, but it provided insight into the beliefs and feelings involved.
Conclusion: Breast is best marginally better
This study is not enough to negate the conclusion that “breast is best,” but it reinforces the conclusion I reached in my earlier article, that breast may be best, but it’s only marginally better than bottle feeding. As the authors of the study comment:
The line between providing information about the benefits of breastfeeding and stigmatizing mothers facing structured, valid, and often difficult trade-offs in the care and financial support of their children or in fulfilling their own human potential must be drawn sensitively.
