TORONTO — Young women today whose grandmothers were exposed to the pesticide DDT may face increased health risks, including those linked to breast cancer and diabetes, a new U.S. study has found.
The study from the Public Health Institute’s Child Health and Development Studies (CHDS) and the University of California at Davis is the very first of its kind to examine the health effects of exposure to a toxic environmental chemical over three generations.
The study, published in Cancer Epidemiology, Biomarkers and Prevention, a journal from the American Association for Cancer Research, found that granddaughters whose grandmothers were exposed to the pesticide DDT have higher rates of obesity and earlier first menstrual periods – which may increase their risk for breast cancer, high blood pressure, diabetes and other cardiometabolic diseases.
DDT – or Dichlorodiphenyltrichloroethane – is a pesticide used in agriculture, but was banned from use in the U.S. in 1972, and suspended from use in Canada in 1985 and eventually banned in 1990.
The study found that despite being banned in the U.S. for nearly 50 years, DDT may have contributed to the falling age of first periods and in obesity rates in young women today.
The study found that risk of obesity of young adult granddaughters was two to three times greater when their grandmothers (who were not overweight) had higher levels of “o,p’-DDT” a contaminant found in commercial DDT in their blood.
Granddaughters were also twice as likely to have earlier first menstrual periods when their grandmothers had higher o,p’-DDT levels. DDT and its contaminants are known to be endocrine disrupting chemicals, or compounds that can alter and interfere with natural hormones that are essential for development.
“We already know that it’s nearly impossible to avoid exposures to many common environmental chemicals that are endocrine disruptors. Now our study shows for the first time in people that environmental chemicals like DDT may also pose health threats to our grandchildren,” said Barbara Cohn, director of CHDS and senior author of the study, in a release.
“In combination with our ongoing studies of DDT effects in the grandmother’s and mother’s generations, our work suggests we should take precautionary action on the use of other endocrine disrupting chemicals, given their potential to affect generations to come in ways we cannot anticipate today,” Cohn continued.
The study followed 20,000 pregnant women and their families in California’s Bay Area for more than 60 years, enrolling them between 1959 and 1967, a time of high pesticide use before DDT was banned.
The “founding grandmothers” in the study gave blood samples throughout their pregnancies at each trimester and one sample shortly after birth.
The blood samples were tested for levels of DDT and its related chemicals, with the current iteration of the study focused on o,p’-DDT as it has been previously linked to breast cancer, obesity and other harmful health effects in offspring, the study says. O,p’-DDT is also the most sensitive biomarker for exposure.
The data suggests that “disruption of endocrine systems by DDT initiates in immature human eggs, decades before the eggs are fertilized,” said Michele La Merrill, associate professor at University of California at Davis and co-lead author of the study.
Researchers did interviews, conducted home visits and obtained questionnaires from the daughters and granddaughters of the original enrollees, also taking blood pressure, height and weight measurements.
The current study is based on 365 adult granddaughters who completed questionnaires, participated in a home visit, had available DDT measures from grandmothers’ serum, and (for 285 of them) had available information on body mass index (BMI) in all three generations. Information on the age of first period for all three generations was available from 235 granddaughters.
Previous studies by CHDS have shown that mothers’ exposure to DDT during pregnancy or immediately after birth correlated with daughters’ increased risk of breast cancer and the prevalence of breast cancer risk factors –including obesity – in adult daughters. Other prior studies have linked DDT exposure to birth defects, reduced fertility and increased risk of diabetes.
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