The insecticide DDT has been banned in the US for over 40 years, but it may still be having an effect on public health.
A long-running California study of more than 15,000 women — covering three generations — found that women who were exposed to DDT in the womb had an increased risk of breast cancer later in life.
Although genetic factors account for about 5 to 10 percent of breast cancer cases, other causes remain unknown. DDT may mimic the female sex hormone estrogen, said the authors of this study. The insecticide might turn certain key genes on and off, which could alter the way a woman’s breast tissue grows and make her more susceptible to breast cancer.
DDT can remain in the human body for many decades.
The initial phase of this study included women in the Kaiser Permanente health insurance program and their infants born between 1957 and 1969. Blood samples were collected and stored close to the time the women gave birth.
Epidemiologist Dr. Barbara A. Cohn has led this study since 1997.
All the mothers in this study had detectable levels of DDT in their blood, according to Dr. Cohn and colleagues. The current study, from the federally funded Public Health Institute, measured DDT levels in two groups of women.
The first group of 188 women had been diagnosed with breast cancer. The second group of 354 women was free of breast cancer.
Women with higher levels of DDT were 3.7 times more likely than those with lower levels of DDT to have been diagnosed with breast cancer. The women with higher levels of DDT were also more likely to have aggressive tumors and to have an advanced stage of the disease at diagnosis.
Most of the population of the US was exposed to DDT between the 1940s and 1970s, when it was sprayed on crops and used in mosquito abatement programs.
DDT exposure is not destiny, however. Even women who were exposed in utero can help protect themselves by eating a healthy diet, avoiding known cancer risks like smoking and talking to a doctor about breast cancer screening.
This study was published in the June issue of the Journal of Clinical Endocrinology & Metabolism.
A number of sources funded this research, such as the California Breast Cancer Research Program, National Institute of Environmental Health Sciences and National Institutes of Health. The authors disclosed no conflicts of interest.