that is used to argue for only small effects using this “gold-standard” method or the sibling study that is held up as showing no differences once that pesky within-family situation is controlled for (you can read about it in detail here
), the research all still suffers from inadequate grouping. Even the more recent Brazilian study that did
find significant and long-term effects of breastfeeding on income, education, and IQ still suffered grouping problems, most notably a lack of an exclusive breastfeeding group (I have covered this research here
if you’re interested).
Despite all of the grouping problems, however, there is a trend in the research that is worthy of consideration: The closer we get to the biological norm for breastfeeding, the more significant the results become. That is, when looking at specific diseases or intelligence or educational attainment or whatever else is theoretically linked to breastfeeding, when exclusive and enduring breastfeeding are included, we almost inevitably see significance in some key areas (luckily no one assumes breastfeeding influences everything).
Using cancer as an example, the research on breastfeeding and childhood cancer is often considered to be mixed, yet the more one looks into the research in detail, patterns emerge that are to do with (a) specific subtypes of cancers, and (b) the length and exclusivity of breastfeeding. In some cases, it’s not until that norm is reached that we can see the risks of formula use. (For a full examination of the breastfeeding-cancer link, read here.) The recent Brazilian research also highlighted this with the effects becoming stronger with a longer duration of breastfeeding and more “predominant” breastfeeding.
What Does This Mean?
Most importantly, going forward we need more studies that actually examine outcomes in groups that include enduring, exclusive breastfeeding, 50% mixed feeding, and 100% formula use to help us understand the effects of both mixed feeding and full formula use. After which we can start to examine the nuances between these groups to determine if there are certain points at which risks start to kick in, for nuances there are, and it’s important for us to understand this.
I realize there is a huge push to argue that “even one breastfeed counts” or the like, but the problem is that this feeds into the notion that breastfeeding is some magical elixir when in fact, it may not be. Our bodies have evolved (or were created) for a type of biologically normal breastfeeding which includes approximately six months of exclusive breastfeeding on demand followed by breastfeeding complementing other foods for years after. Although a look at the ingredient list between breast milk and formula definitely highlights the real difference between the two, it’s really unclear how much breastfeeding is necessary to meet our biological norm. Or rather, how much formula changes our biological norm. Notably, this research shouldn’t be undertaken to shame anyone, but to help us better understand how our moving away from what is evolutionary or biologically normal influences our health in the short- and long-term.
Equally importantly, we need everyone to understand that the effects of breastfeeding (or not) are dynamic, not static. They will differ based on one’s personal experiences, genetic make-up, environment, and so on. Understanding these nuances is central to getting a better idea of how to help families and children. In addition to the grouping problem, we also have the problem that breastfeeding is assumed to influence each individual the same way yet that’s likely not true. For example, a child exposed to various environmental toxins or various diseases is likely going to benefit more from the influence of breastfeeding than a child in a healthier environment to begin with. In one case, it may be the difference between life and death, the other, only small differences.
With respect to how we’ve interpreted the data as a whole thus far, it is clear that the studies we have are far from perfect. It also means that all these studies that purportedly have found no differences are very conservative estimates of any effect of breastfeeding/risk of formula and people should be aware of this, especially if people are going to bring up the SES issue. You see, when people bring up the SES issue, they should also be willing to admit that although that may bias results liberally, a far greater concern is with the groupings which has a much greater chance of biasing results conservatively.
Why is this concern greater? Because SES variables are being included and controlled for, therefore the main concern remains with causality and residual confounding. That is, we still cannot say the effects are definitely causal, only correlational, and there may be other effects of SES that we haven’t controlled for that would influence the findings. Now, we have some studies that actually do demonstrate potential causality (see here for an example), but we cannot control for residual confounding and thus it remains problematic. However there is no control for the grouping problem. Once someone is in a group, they are there for better or worse, and when our groups are so loosely defined, trying to extrapolate the data to others becomes incredibly difficult. Frankly, given this, I’m always amazed when any research finds any effects of breastfeeding.
The real question, however, and one we need to consider moving forward, is whether we can even examine the real effects of breastfeeding in a society where biologically normal breastfeeding is so rare. Not only is there a huge social push away from this type of breastfeeding, but even finding women who are exclusively breastfeeding at six months is difficult as our cultural norms are so very far from our biological norms.
Breastfeeding research is flawed, though not only in the way that most formula apologists would like you to believe. If we are ever going to truly understand the amazing nature of breast milk and breastfeeding, we need to start looking at it from its evolutionary basis as not only food, but something more that has helped us thrive and survive against what would seemingly be all odds.
If you are in need of individualized parenting help, I offer services via email, Skype, and phone on a variety of parenting topics. You can find out more here.
 Kramer MS, Chalmers B, Hodnett ED, Sevkovskaya Z, Dzikovich I, et al. Promotion of breastfeeding intervention trial (PROBIT). JAMA
2001; 285: 413-20.
 Colen CG, Ramey DM. Is breast truly best? Estimating the effects of breastfeeding on long-term child health and well-being in the United States using sibling comparisons. Social Science & Medicine
2014; 109: 55-65.
 Victora CG, Horta BL, de Mola CL, Quevedo L, Pinheiro RT, et al. Association between breastfeeding and intelligence, educational attainment, and income at 30 years of age: a prospective birth cohort study from Brazil. The Lancet Global Health
2015; 3: e199-e205.