(HealthDay News) — Although the pesticide dichlorodiphenyltrichloroethane (DDT) was banned in the United States in 1972, women exposed to the chemical in utero may be more likely to develop breast cancer than women who had less exposure, according to a study published in the Journal of Clinical Endocrinology & Metabolism.
Barbara Cohn, PhD, MPH, director of the Child Health and Development Studies at the Public Health Institute in Berkeley, California, and colleagues tracked 20,754 pregnancies among women who were members of the Kaiser Foundation Health Plan from 1959 through 1967. The women gave birth to 9,300 daughters during those years.
The researchers looked at DDT levels in the mother’s blood samples during pregnancy or soon after childbirth. Until 2012, they also tracked whether or not breast cancer developed in the daughters of these women by age 52 years.
During the 54-year follow-up period, the researchers examined DDT levels in mothers of 118 daughters who developed breast cancer. They compared these women with 354 women from the group who didn’t develop breast cancer.
The researchers found that women exposed to the highest levels of DDT in utero had a 3.7 times higher risk of breast cancer than those who had the lowest exposure to DDT. The higher the DDT levels in the mother’s blood samples, the more likely a woman was to be diagnosed with more advanced breast cancer, according to the study.
This link held strong even after Cohn’s team took into account the mother’s history of breast cancer.
Most of the women with breast cancer (83%) had estrogen-receptor positive cancer. Prior research has suggested that DDT may have a weak estrogen-like activity, according to the study authors. However, Cohn told HealthDay that she doesn’t know what the mechanism might be behind the link between DDT exposure and breast cancer risk.