Breast milk vs. formula: What do the studies really tell us?
A closer look at the factors influencing studies that look at the potential health benefits of breast feeding.
Editor's note: This is the second of two parts on breast feeding and formula feeding.
In part one, we saw that it is commonly believed today that breastfeeding is superior to formula feeding for children's' health. It's not hard to see why many advocates and scientists have reached this conclusion. Study after study comparing breastfed and formula fed infants, seem to show that breastfed babies had superior IQs and suffered less illness.
But we found that there are serious issues with these conclusions. Essentially, all the studies ever done on this topic fail to account for other factors that may lead to those outcomes (health and IQ). For example, a mother's high IQ predicts that her children will likely have higher IQ, but also that she will nurse them. Parents who use formula tend to be poorer and live in environments in which children have a tendency to experience more illness. It's a classic chicken-and-egg dilemma. This problem could be prevented if randomized studies were done on this topic, but, understandably, those are considered unethical.
Luckily, there are a few studies that help shed light on this problem. Emily Oster, PhD, an associate professor of economics at Brown University, discusses them in this article. One such study, is the PROBIT trial. Here, groups were randomized into two: one group received breastfeeding support while the other did not.
The support received is described as: "Baby-Friendly Hospital Initiative [BFHI]…which emphasizes health care worker assistance with initiating and maintaining breastfeeding and lactation and postnatal breastfeeding support." Infants were followed for one and a half years after birth and then had a one year follow-up check after that. The results were as follows:
1. At three months 43 percent of those who received BFHI support were still breastfed exclusively vs. only 6 percent in the other group (that's a very large difference!)
2. Nine percent of breastfed infants had at least one illness with diarrhea vs. 13 percent in formula fed infants
3. Three percent of breastfed infants had eczema vs. 6 percent formula fed
4. There were no differences in the number of common colds
This tells us that breastfed babies do suffer less often from diarrhea and eczema, but by a relatively small difference. And…that's it.
There's another way to work around the problem that randomized trials can't be ethically conducted in breastfeeding: sibling comparisons. In this method, you look at the same family, but compare siblings to each other, when one was breastfed and the other formula fed. The beauty here is that, more or less, all the other factors are kept the same such as the parents, environment, and foods.
In "Is Breast Truly Best?" the researchers set out to remove the effects of confounders on the data. They used a very large study which followed about 12,000 children from all walks of life from birth until age 14. This study was particularly helpful not only because it was large, but also because it followed very diverse groups of families. Then, they focused on sibling data in situations where each child was fed differently and, the results were stunning. When they looked at "between-families", the data showed that breastfeeding was "associated with beneficial long-term child outcomes. This trend was evident for 10 out of the 11 outcomes examined here." These outcomes included differences in IQ. But when they flipped the statistical "sibling switch" on and accounted for all the confounders they reported that those associations disappeared and they were "forced to reconsider the notion that breastfeeding unequivocally results in improved childhood health and wellbeing."
There are some special considerations when thinking about the benefits of formula or breastfeeding. It's obvious that these comparisons are only applicable to populations that have formula as an alternative. In impoverished nations, where mother's milk is the only option, there is nothing comparable. It should also be noted that there is some evidence that suggests that breastfeeding for a year or longer can reduce the risk of maternal breast cancer. Also, breastfeeding has been shown in several studies to be superior to formula for premature infants in preventing complications of prematurity.
What we know today about breast feeding is based on many studies, but almost all those studies suffer from significant flaws. That is not, in any way, an "anti-breastfeeding" statement. Rather, it's a statement about supporting those women who choose not to, or can't breastfeed. Every pediatric practitioner can tell you that nursing can take an emotional and physical toll on some women. When those women forgo nursing, they should be reassured that their babies' health outcomes and IQ's will likely be just as positive.
Unfortunately, women can experience shaming and guilt when they choose to skip nursing. For many, nursing is a joy and offers a break in the day when mother and child can be physically attached. But we should not forget good mothering (and fathering) consists of many, many factors which transcend the methods of feeding. Perhaps the most truthful statement, ultimately is "fed is best."