The most important long-term impact is actually on the health of the mother

Thursday, April 25th, 2019

Emily Oster, economist and author of Cribsheet: A Data-Driven Guide to Better, More Relaxed Parenting, From Birth to Preschool, explores the data all guilt-ridden parents need:

Some of the best evidence on breast-feeding comes from the Promotion of Breast-Feeding Intervention, or Probit, study, a large randomized trial from the 1990s run in Belarus, in which some of the mothers received breast-feeding guidance and support and some didn’t. Based on this data, the most well-supported benefits of breast-feeding are lower risks of gastrointestinal infections (with symptoms like diarrhea or vomiting) and of rashes and eczema early in life. To put some numbers to it, the study found that of the babies of a group of mothers encouraged to breast-feed, 9 percent had at least one episode of diarrhea, compared with 13 percent of the children of mothers who weren’t encouraged to breast-feed. The rate for rashes and eczema was 3 percent versus 6 percent.

Yet the study found no effect on respiratory infections, including ear infections, croup and wheezing. So why do we continue to see the “evidence-based” claim that breast-feeding reduces colds and ear infections? The main reason is there are many observational studies that do show that breast-feeding affects these illnesses.


One study of Scandinavian 5-year-olds found that children who nursed longer had cognitive scores that were nearly 8 points higher on average. But their mothers were also richer, had more education and had higher I.Q. scores. Once the authors adjusted for even a few of these variables, the effects were much smaller.

In fact, the most compelling studies on this compare siblings, one of whom was breast-fed and the other not; these find no significant differences in I.Q. This same type of sibling study has also looked at obesity and, again, found little to no impact.


However, there is real evidence base for a link between breast-feeding and cancers, in particular breast cancer. Across a wide variety of studies, there seems to be a sizable effect — perhaps a 20 percent to 30 percent reduction in the risk of breast cancer for women who breast-feed for longer than 12 months. In addition, the case for causality is bolstered by a concrete set of mechanisms. Researchers suggest that breast-feeding changes some aspects of the cells of the breast, which make them less susceptible to carcinogens.

After all that focus on the benefits of breast-feeding for kids, it may be that the most important long-term impact is actually on the health of the mother.


  1. Kirk says:

    Stop and think about something, for a moment: What signal is a mother who doesn’t breastfeed sending back to nature…? Key one: She’s not a successful mother, so why shouldn’t the genes be biased towards taking her out of play earlier than normal, because she didn’t breed…?

    We’re all the expressions of long conversations between the environment and our gene pool. If you stop and think about it, it’s not so strange that some of the things we’re saying back to that gene pool are going to result in us getting some negative feedback. Long-term bachelors who don’t mate or procreate…? What use are they? So, why shouldn’t the gene pool cull those individuals?

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