(Beyond Pesticides, August 7, 2007) In a study that examines the influence of age of exposure on the magnitude of the association between DDT and breast cancer risk finds that women who were exposed to DDT before the age of 14 are five times more likely to develop breast cancer later in life. In contrast, the study finds exposure after adolescence does not increase risk.
The data used in the study targets the age of a woman in 1945 as an indicator for the youngest possible age for a woman to be exposed to DDT, since DDT was first introduced to the U.S. for mosquito control in 1945. The researchers, from the Center for Research on Women’s and Children’s Health, Public Health Institute at Berkeley, California and the Mount Sinai School of Medicine, analyzed blood that had been collected from women between 1959 and 1967 – years during which the use of DDT was at its highest.
“DDT and breast cancer in young women: New data on the significance of age at exposure,” published last week in the online edition of the journal Environmental Health Perspectives, is “the first study specifically designed, a priori, to consider whether age at exposure may modify DDT effects on breast cancer.”
The health records for the women studied were collected from the California Cancer Registry and the California Vital Status Records. The researchers identified those who were diagnosed with breast cancer before age 50, or those who had died because of breast cancer before age 50. Of the women whose blood was stored, 129 cases were used to measure three forms of DDT: p,p’-DDT, o,p’-DDT, and p,p’-DDE. These cases were divided into groups based on what their age would have been in 1945 and included groups younger than 4 years old, 4-7 years, 8-13 years and >13 years old, and paired them with control groups.
After analysis, DDT was found to be present in all subjects. However, for those that developed breast cancer, DDT was at much higher levels than for those who did not. Those younger than 14 in 1945 with the highest levels of exposure were 5.4 times more likely to have breast cancer. In contrast, there was no relationship between exposure level and breast cancer for women who were 14 years and older in 1945. The researchers also found that those exposed at the youngest age had the highest risk for developing breast cancer.
These findings add to the growing number of studies that show exposure to chemicals that are hormonally active can lead to diseases such as cancer.
The recurring message is that exposure to these chemicals at critical periods in the body’s development, in this case pre-adolescent breast development, has long terms effects that manifest as adult onset of disease, such as cancer, later in life. Also important to note is that women who would have been exposed to DDT during the 1950s and 1960s have not yet reached the age of 50 – the age of greatest breast cancer risk is around age 60. This means that the significance of these findings may be larger.
According to Barbara Brenner, executive director of San Francisco-based Breast Cancer Action, “We have to start paying very close attention to what we put in our environment. This is an example of doing something to our environment where we did not understand the long-term consequences. I don’t know how many times this story has to be told.”
However, the study does not account for other known risk factors that may have predisposed the women toward cancer. Researchers also don’t know when the women were exposed to DDT. Co-author of the study Dr. Mary Wolff, Ph.D., a professor of oncology at Mount Sinai School of Medicine remarked, “I don’t think it’s just early life exposures. Most cancers are an accumulation of a lot of factors.”
Their conclusion is carefully worded: “It is too soon to decide that DDT exposure has little public health significance for breast cancer risk. We based this conclusion on 1) the long latency of possible effects on breast cancer, 2) the large numbers of women exposed world-wide, and 3) the evidence that we provide here which suggests that women exposed when young may be most strongly affected.”
They also note “the public health significance of DDT exposure is potentially large.”
This is important because the costs and benefits of DDT in respect to public health are still being weighed. DDT, or dichloro diphenyl trichloroethane, while highly persistent in the environment, was initially found to be effective against mosquitoes and the diseases they carry such as malaria. However, insect resistance to the chemical has been documented since 1946, DDT was banned in the U.S. in 1972 after it was linked to the decline of the bald eagle and other raptors, and it continues to be linked to health problems. The benefits of the use of DDT for mosquito control are still debated, especially in developing nations that are plagued with high infection rates of malaria. Some countries are continuing to use DDT to prevent malaria, while others insist that the health and environmental risks are too great citing alternatives and an international agreement to phase-out the remaining uses of the persistent chemical.
See the Washington Post’s October 9, 2007 coverage of this issue.