Women exposed to higher levels of the once-ubiquitous pesticide DDT while in utero face a nearly fourfold increased risk of developing breast cancer, according to the results of a five decade long study of U.S. mothers and daughters.
Researchers evaluated 54 years of data from women starting from the time they were in utero. Out of 9,300 women who had been tracked from before birth, the study authors identified 118 women who had been diagnosed with breast cancer by age 52. Women whose mothers had elevated blood levels of DDT during pregnancy were four times as likely to have had breast cancer as their counterparts who had been exposed to a small quantity of the pesticide, even after controlling for known risk factors such as family history and age, the study found.
The research, published in the Journal of Clinical Endocrinology & Metabolism, shows “direct evidence” that higher DDT exposure in the womb places women at increased risk of breast cancer, said study author Dr. Barbara Cohn, PhD, a researcher at the Public Health Institute in Berkeley, CA.
“Environmental chemicals have long been suspected causes of breast cancer, but until now, there have been few human studies to support this idea,” she said.
DDT behaves like a synthetic estrogen hormone, and when in contact with insects it cause seizures, leading to death. In humans, the estrogen hormone is involved in signaling breast cells to grow and divide.
Among the women who were diagnosed with breast cancer during the study period, 83 percent had estrogen-receptor positive breast cancer, a form of cancer that is fueled by the hormone estrogen. Exposure in utero to DDT was also associated with more advanced tumors at the time of diagnosis and with a particularly aggressive type of malignancy known as HER2-positive breast cancer. In lab studies, DDT has been found to interfere with the function of estrogen and, separately, to activate the HER2 protein, which may explain the link to these specific types of breast cancer.
The United States has banned DDT, one of the first known endocrine-disrupting chemicals, since the 1970s. Still, many potentially affected women who were born that era are just reaching the age when they are at increased risk for breast cancer.
Furthermore, despite extensive research documenting the many health risks of DDT—the pesticide has been linked to Alzheimer’s disease, obesity and diabetes, infertility, and diseases of the liver, skin, nervous system—some countries still use the chemical to fight malaria. The study authors say policymakers should consider the study as they evaluate whether to continue using DDT. It should be noted, however, that some of the “safer” alternatives to DDT have recently been linked to serious health effects including metabolic dysfunction, fertility problems, and kidney and ovarian diseases.