Chemicals in Breast Milk: Little Data to Date.

Breast milk offers infants unparalleled nutrition to fuel their growth and development. It also provides a host of immune factors that can increase their resistance to common infections. Additionally, breast-fed infants may have a reduced risk of developing chronic diseases such as diabetes, allergies, and asthma. By breast-feeding her infant, a mother herself receives several health benefits, including less postpartum bleeding, a quicker return to prepregnancy weight, and a potentially decreased risk of ovarian and breast cancers. However, some new mothers hesitate to breast-feed due to concern about environmental chemicals in their breast milk. Although the benefits of breast-feeding outweigh the risks of low-level chemical exposures, more information is necessary to dispel concerns.

In a review of the literature on environmental chemicals in breast milk, Judy S. LaKind and colleagues from the Pennsylvania State University College of Medicine and the Johns Hopkins University Department of Mathematical Sciences demonstrate that the data, particularly in the United States, are sparse [EHP 109:75-88]. Their review focuses on two aspects of exposure: chemical concentrations in breast milk and their trends over time.

Environmental contaminants such as polychlorinated dioxins and furans, polychlorinated biphenyls, and chlorinated organic pesticides have been detected at low concentrations in breast milk throughout the world. Among other risks, these chemicals are suspected of subtly damaging the immune system, causing developmental delays, and increasing an exposed person's lifetime cancer risk. The chemicals, which accumulate in body fat over the course of a person's life, are mobilized during lactation and excreted in breast milk.

LaKind and her associates identify several problems that impede the forming of general conclusions. In the United States, there are uncertainties regarding whether breast milk samples have been collected in a way that allows for comparison from one study to another, and the data that exist pertain only to a limited number of women from specific locations. Data from other nations, particularly in Europe, are more thorough, but, as with the data from the United States, cross-study comparisons are difficult because of inconsistent protocols and nonreported information. One variable that is particularly overlooked is depuration (the elimination of environmental chemicals from the mother's body through breast milk) over the course of lactation. Among other factors, depuration may be influenced by a mother's age, how many children she's had, and how much milk her infant consumes. One-time samples therefore do not account for changes in breast milk concentrations over the course of lactation.

The reviewers suggest that the inadequacies of current data could be addressed through a carefully planned and coordinated breast milk monitoring effort. Such a monitoring program could include women from throughout the United States and could represent diverse socioeconomic and demographic groups. Data collection could build on earlier studies by including both previously studied chemicals as well as other environmental contaminants such as heavy metals.

To control for depuration differences, milk samples could be collected longitudinally. Finally, to extract the maximum information from the data, sampling and testing methods would have to be in harmony across different studies. According to LaKind and her colleagues, a well-planned monitoring program would provide reliable information to doctors, nurses, and lactation specialists, and help them communicate the benefits of breast-feeding to new mothers.

It is also necessary, the reviewers say, to assess the concentrations of environmental contaminants in other infant food sources, such as formula, in order to compare the risks and benefits associated with all sources of infant nutrition.