Breastfeeding in the Age of Chemicals

It’s a catch-22 that would drive any new mother crazy.

Should she breastfeed, which is linked to many lasting health benefits for the newborn child, but take the risk of delivering toxic chemicals, such as dioxins and DDT, that are stored in her breast milk?

Or, should she use infant formula, which avoids the problem of breast milk contaminants but does not offer the same benefits to her newborn and may also contain toxic chemicals (because of lax food safety regulations or if contaminated water is used to reconstitute the formula, for example).

Last month, two papers (from the same group of collaborators) published in Environmental Health Perspectives attempted to address these issues by reviewing decades of relevant research. These papers are both quite extensive and represent impressive work by the authors – but it’s unlikely that non-scientists will wade through the details. So, I’ll do my best to help you out.

Breast milk vs. infant formula: What chemicals are in each?

The first paper starts by documenting all of the chemicals detected in either breast milk or infant formula, based on studies published between the years 2000-2014 (mostly in the United States). Below is a highly simplified table, with just the chemicals rather than other details (refer to the paper if you’re interested in more).

Screen Shot 2018-10-10 at 8.52.42 PM
Abbreviated list of chemicals detected in breast milk and infant formula in studies of women in the United States between 2000-2014. Adapted from Lehmann et al, 2018.
*No data from US studies, so information taken from international studies


What can we learn from these data, other than that it looks like complicated alphabet soup?

Well, toxic chemicals have been detected in both breast milk and infant formula, but there are some differences in the types of chemicals found in each. Breast milk is more likely to contain lipophilic (fat-loving/stored in fat) and long-lasting chemicals, such as dioxins and certain pesticides. By contrast, breast milk and formula both have some common short-lived chemicals, such as bisphenol-A (BPA) and parabens.

While the paper also provides information about the average and range of concentrations of chemicals in each medium (and how they compare to acceptable levels of exposure for infants), it’s hard to draw general conclusions because there are such limited data available. It is complicated, expensive and invasive to get samples of breast milk across wide segments of the population, and relatively few studies have looked at chemicals found in infant formula. We need more information before we can accurately understand the patterns of exposure across the population.

Nevertheless, the presence of all of these chemicals seems concerning. No one wants to deliver toxic milk to children during their early months of life, when they are more vulnerable because their organ systems and defense mechanisms are still developing.

But, what do the data indicate about the health consequences of these exposures?

Early dietary exposures and child health outcomes

That’s where the second paper comes in. Here, the same group of authors reviewed the literature on the association between chemicals in breast milk and adverse health outcomes in children. (Note: they had planned to ask the same question for infant formula, but there were not enough published studies). They looked at many chemicals (such as dioxins, PCBs, organochlorine pesticides, PBDEs) and many outcomes (including neurological development, growth & maturation, immune system, respiratory illness, infection, thyroid hormone levels).

Early studies in the field had indeed suggested cause for concern. For example, infants in Germany fed breast milk contaminated with high levels of PCBs were found to have neurodevelopmental deficits in early life. However, levels of PCBs in the general population have declined in recent years (because of worldwide bans), and subsequent studies in the same region found that these lower levels of PCBs were not associated with harmful neurodevelopmental effects.

Overall, when looking across various chemicals and health outcomes, the current literature is actually… inconclusive. Many studies reported no associations, and studies asking similar questions often reported conflicting results. Furthermore, studies that reported significant effects often evaluated health outcomes at only one or two periods in early life, and we don’t know if those changes really persist over time.

A glass half full…of challenges

In the end, the authors ended up with more questions than answers – and a long list of challenges that prevent us from understanding the effects of breast milk-related chemical exposures on children’s health. For example:

  • Chemicals in breast milk are often also present in the mother during pregnancy. How can we disentangle the effects of exposures during the prenatal period from exposures due only to breast milk in early postnatal life?
  • Many of these studies represent a classic case of “looking for your keys under the lamppost.” We can only study chemicals and outcomes that we choose to focus on, so we could be missing other important associations that exist.
  • On a related note, most studies focused on exposure to only one or a small group of chemicals, rather than the real-world scenario of the complex mixtures in breast milk.
  • There was little study replication (ie: more than one study looking at the same question). Generally, we feel more confident drawing conclusions based on a larger pool of studies.
  • The few studies that did ask the same questions often used different experimental designs. These distinctions also pose challenges for interpretation, since differences in how researchers measure exposures and outcomes could affect their results.
  • Most studies evaluated levels of chemicals in breast milk using one or two samples only. How accurate are these exposure assessments, given that levels in the milk may change over time?
  • Measuring chemicals in breast milk is just one aspect of exposure, but it doesn’t tell us how much the infant actually received. Mothers breastfeed for different amounts of time, which affects how much is delivered to the infant. These person-to-person differences within a study could make it challenging to see clear results in an analysis.

Filling in the gaps

Perhaps the only certain conclusion from these publications is that much work remains. Not only do we need more studies that document the levels of chemicals in breast milk and infant formula (as the first paper highlighted), but we also need more data on the links between these exposures and health outcomes – including targeted research to address the challenges and key gaps noted above.

Importantly, because breastfeeding is associated with many key health benefits (such as improved neurodevelopment and reduced risk of obesity, diabetes, infections, and more), any study that looks at the impact of chemical exposures in breast milk should also ask a similar question in a comparison group of formula-fed infants. It is likely that the positive effects of breast milk far outweigh any potential negative impacts from the chemicals in the milk, and that the infants would actually be worse off if they were fed formula that had the same level of chemicals (but did not receive the benefits of breast milk).

I’ll be the first to admit: it is scary to think about all of these chemicals in breast milk. But, all decisions have trade-offs, and here, when weighing the risks and benefits, the balance still seems to favor breastfeeding in most situations.

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