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© Reuters / Stringer
Blood samples taken from pregnant mothers showed that exposure to high levels of the pesticide DDT resulted in daughters with nearly four times the rate of breast cancer, according to a new study.

Researchers followed 9,300 women born between 1959 to 1967, when the insecticide DDT was widely sprayed on lands and agriculture. When taking into account the history of these women's mothers, the study found that they had a 3.7 times higher risk of breast cancer if they had been exposed to the insecticide in utero.

"It has long been suspected that environmental chemicals that interfere with hormone systems could be connected to risk of breast cancer. Here we found the first direct connection for measured levels of DDT in mothers' pregnancy blood," the study's lead author, Barbara Cohn, director of child health and development studies at the Public Health Institute in Berkeley, California, told Reuters.

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. The current study reviewed blood tests for DDT levels in 20,754 women who had given birth in Oakland, California during the 50s and 60s.

Of the 9,300 daughters of these women studied by scientists using state cancer registry records, 137 had developed breast tumors by the age of 52. Some of the daughters were excluded because there was no data on their mother's exposure to DDT, but of those remaining, 103 had developed tumors. Of those women with tumors, 83 percent were fueled by the hormone estrogen, and 76 percent by the hormone progesterone.

The EPA lists DDT as a probable carcinogen, but previous research has been mixed about its link to breast cancer.

RT's Lindsay France reported that "the study's authors say their findings support the classification of DDT as an endocrine disruptor, a predictor of high risk breast cancer and a marker of high risk. All of this will require massive further study."

Scientists involved in the study, published in the Journal of Clinical Endocrinology and Metabolism, knew that similar in utero studies had found links between synthetic estrogens and an increased risk of breast cancer, but there was no study showing links to the use of DDT, which was widely used in the 1960s. The pesticide is still widely used in Africa and Asia to help control malaria-spreading mosquitoes.

Worldwide breast cancer is the most common malignancy in women, with about one in nine women eventually developing the disease, according the National Institutes of Health.