A study done by the Public Health Institute in Berkeley, Calif., suggests that women who were exposed to higher levels of the pesticide DDT while they were in the womb were nearly 4 times more likely to be diagnosed with breast cancer as adults than women who were exposed to lower levels before birth.
The research was published online on June 16, 2015 in The Journal of Clinical Endocrinology & Metabolism. Read the abstract of “DDT Exposure in Utero and Breast Cancer.”
DDT stands for dichlorodiphenyltrichloroethane. DDT was used widely throughout the United States to control insect pests in crops from 1939 until 1972, when the Environmental Protection Agency outlawed its use. Though many other countries have banned it, DDT is still used to fight malaria in Sub-Saharan Africa and Asia.
The chemical breaks down incredibly slowly and accumulates in the fatty tissues of animals (including people). Many people exposed to DDT 30 or 40 years ago still have traces of it in their bodies.
DDT is an endocrine disruptor, which means it acts like a hormone or affects how other hormones act in the body. Endocrine disruptors throw off the body’s hormonal balance by blocking or mimicking hormones, such as estrogen. Earlier studies have linked DDT to birth defects, a higher risk of Type 2 diabetes, and fertility problems.
In this study, the researchers tracked the 9,300 daughters born to women who participated in the Child Health and Development Studies (CHDS) for 54 years. The CHDS started when the women were pregnant, so the daughters have been followed since they were in the womb. The women were all members of the Kaiser Foundation Health Plan from 1959 to 1967.
By using state records and surveying the daughters, the researchers figured out how many of them had been diagnosed with breast cancer by age 52.
To determine the level of DDT the daughters were exposed to in the womb, the researchers analyzed stored blood samples from the CHDS to measure DDT levels in the mothers’ blood during pregnancy or immediately after giving birth.
The researchers measured DDT levels in the mothers of 118 daughters who were diagnosed with breast cancer. They also measured DDT levels in the mothers of 354 daughters who were not diagnosed with breast cancer so they could compare the levels.
The researchers found that higher levels of DDT in the mother’s blood were linked to a breast cancer risk nearly 4 times higher than average in the daughter. This link was seen no matter what the mother’s history of breast cancer was.
Among the daughters diagnosed with breast cancer, 83% were diagnosed with estrogen-receptor-positive disease, which receives signals from the hormone estrogen to grow.
Higher levels of DDT in the mother’s blood also were linked to daughters being diagnosed with:
- a more advanced stage of breast cancer
- HER2-positive breast cancer
Earlier studies have shown that DDT activates the HER2 protein.
“This 54-year study is the first to provide direct evidence that chemical exposures for pregnant women may have lifelong consequences for their daughters' breast cancer risk,” said Barbara A. Cohn, Ph.D., of the Public Health Institute in Berkeley, Calif., and one of the study’s authors. “Environmental chemicals have long been suspected causes of breast cancer, but until now, there have been few human studies to support this idea.
“This study calls for a new emphasis on finding and controlling environmental causes of breast cancer that operate in the womb. Our findings should prompt additional clinical and laboratory studies that can lead to prevention, early detection, and treatment of DDT-associated breast cancer in the many generations of women who were exposed in the womb. We also are continuing to research other chemicals to see which may impact breast cancer risk among our study participants.”
While this study is extremely concerning, it’s important to know that the hazards of chemical exposures depend on a lot of things, including the amount of exposure, the frequency of exposure, the duration of exposure, and the age when exposed. While we can’t get rid of any chemicals that are already inside us, there are steps you can take to minimize any further exposure:
- consider buying organic food; if cost is an issue, the Environmental Working Group’s Shopper’s Guide to Pesticides lists, the “Dirty Dozen and “Clean Fifteen,” can help you decide which fruits and vegetables to buy organic
- wash and peel your produce
- trim fat from fish, beef, and other meats
- install a filter on the taps in your house or store drinking water in a pitcher with a filter; installing a reverse osmosis system is another, more expensive, option
For more information on breast cancer risk factors and steps you can take to minimize each in your own life, visit the Breastcancer.org Lower Your Risk section.