When parents cannot breast-feed an infant (when a child is adopted, when a mother’s health or medical history precludes nursing or when a mother can’t produce enough milk), most parents turn to formula. Donated breast milk – milk pumped by another mother and then donated personally, via a milk bank, or through informal sharing network – is still an option pursued by a relatively small group of parents, although many neonatal intensive-care units are increasingly seeking donor milk for premature infants to reduce the risk of a potentially fatal condition called necrotizing enterocolitis.

Nicolas Bakalar, reporting in The New York Times about a study published in the journal Pediatrics, wrote that the study “found that breast milk bought from two popular Web sites was often contaminated with shigh levels of bacteria, including, in a few instances, salmonella. The amounts detected in some samples were sufficient to sicken a child.” (Breast Milk Donated or Sold Online Is Often Tainted, Study Says)

The contamination was found in a lab setting, and what’s not known is how such contamination may affect an infant. The researchers examined 101 samples, Bakalar, writes, and found that “64 percent of the samples from milk-sharing sites were contaminated with staph, 36 percent with strep, and almost three-quarters with other bacterial species. Three of the samples contained salmonella. Seventy-four percent of the samples would have failed milk-bank criteria.”

None of that is appealing, and if I offered you a bottle of donor milk for your baby that I identified as contaminated with staph, strep or salmonella, you would likely take a pass. The study concerns health officials (as it should). But what does it mean for a parent choosing among the options for an infant who cannot be breastfed, but may still benefit from breast milk? As Suzanne Barston, author of “Bottled Up: How the Way We Feed Babies Has Come to Define Motherhood, and Why It Shouldn’t” put it in a post on her website, Fearless Formula Feeder, that’s well worth a read, this is an opportunity to “discuss the substance rather than the behavior.”

So my headline reflects the question this study gives us the opportunity to ask. Breast milk is a substance, with certain risks and benefits. Breast-feeding is a behavior, with certain benefits and costs. Some researchers even argue that neither the substance nor the behavior leads to the association between breast-fed babies and better health, positing that “if a mother is able to breast-feed, and does so, this ability is essentially proof that the baby has already had an optimal life inside the womb.” (That’s singularly unhelpful here, but may be comforting for some parents.)

Breast milk is a living substance that alters depending on variables like the age of the infant the mother’s body intends to feed, her environment or her health. Banked breast milk has some of the same variations, and is also pasteurized, which destroys many contaminants, viruses and bacteria, but destroys some beneficial substances as well. (It can also be expensive and difficult to get, depending on your circumstances.) Formula is just that: a formula, a predictable substance, made according to very specific, narrowly defined parameters, but with its own risks of contamination. Breast milk is commonly associated with a number of improvements in baby and maternal health; but its value, particularly in societies with access to clean water and a consistent food supply, has been passionately debated.

For research-reading parents, this is a classic case of “Wow, do we need more information,” and that information is surprisingly hard to find and interpret. In the case of the premature infant, the science supporting the use of donor milk is clear. Beyond that, it’s murky, and interpretations are often colored by emotion. As different compounds in human breast milk are shown to be associated with improved baby health, formula manufacturers rush to add them to their products, but there is still much we don’t know about the specifics of the interaction between breast milk and baby.

If you’ve chosen donor milk for a baby, or rejected it, what helped you to make that decision? If you donate, do you choose to give milk to a milk bank, or sell or donate informally? How can science help future parents to make these calls?

An earlier version of this post stated that I “could not find any reported cases of babies sickened by donor breast milk.” A reader has since referred me to this 1977 case of a single donor contaminating 7 babies in a neonatal intensive care unit, which led me to a similar 1979 case. Standards for donation and storage of breast milk in milk banks have changed considerably since then, and I have not found more recent cases, nor have I found any associated with online milk-sharing sites – but coverage of this recent study has made that a particularly difficult area to search. If anyone is aware of any documented case of a baby being sickened from donor breast milk associated with these sites, email me and I’ll follow up.

Contact KJ Dell-Antonia at:[email protected]

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