22. CHEMICALS: Concentrations in mothers' milk don't decrease over time -- study (07/13/2009)

Sara Goodman, E&E reporter

New research suggests that levels of persistent organic chemicals in the milk of breast-feeding women do not decrease over time, a finding that could improve researchers' ability to determine infant exposures to environmental chemicals, according to a new study.

Scientists have believed for some time that exposure to chemicals -- such as the now-banned DDT, which persists in the environment and the human body for decades -- through breast-feeding declines over the course of lactation. This is because studies that have looked at levels of various chemicals in breast milk at different times post-birth supported the hypothesis that as a woman breast-fed, her stores of lipids and lipid-associated environmental chemicals would be activated from where they were being stored and excreted through her breast milk.

But the model that researchers use to determine exposure levels based on this hypothesis is likely "too simplistic," the researchers concluded in the new study, published in the journal Environmental Health Perspectives. They added a component to those previous studies by simultaneously taking blood and milk samples of 10 women twice following birth. They also looked at additional milk samples without correlating blood samples. The researchers found that levels of persistent organic chemicals did not decrease during lactation, and actually increased for some women.

This is significant because early childhood exposure assessments traditionally have included decreasing breast milk concentrations during the course of breast-feeding, the researchers note. Furthermore, this research suggests that pumping and discarding milk early on in an effort to reduce exposure is likely not beneficial.

In conclusion, the researchers pointed out that the relationship of the chemicals to the breast-feeding process was more complex than has been understood. It is still unknown why some women saw decreased levels, while others remained the same or increased, for example. The study points out the need for further research into the relationship between the chemicals and blood and milk concentrations.

They also suggested two potential avenues for further research -- weight loss following birth and current diet. These are hypotheses that need further study, the researchers caution, noting that "the controlling factors are likely numerous and complex." They also recommend a larger study to try to replicate these results.

Click here to read the study.