Women who were exposed to
high levels of the pesticide DDT while in the womb are at a four-fold greater
risk of developing breast
cancer than those exposed to lower levels, according to a new study. The
research, published June 16 in the Journal
of Clinical Endocrinology and Metabolism (JCEM), found evidence of a link
between women exposed to DDT during their pregnancy and the risk of breast
cancer to their daughters.
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| Breast Cancer and DDT |
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“Environmental chemicals
have long been suspected as causes of breast cancer, but until now, there have
been few human studies to support this idea,” study author Barbara A. Cohn,
PhD, director of Child Health and Development Studies at the Public Health
Institute in Berkeley, Calif., said in a news release.
Banned in the U.S. since
1972, DDT was one of the first pesticides to be
recognized as an endocrine disruptor – a group of chemicals that interfere with
the body’s endocrine
system and produce adverse developmental, reproductive, neurological, and
immune effects in both humans and wildlife. Previous studies found that
exposure to DDT was associated with birth defects, reduced fertility and an
increased risk of type 2 diabetes, but links to breast cancer were weak --
until now.
For the new study, Cohn
and her colleagues tracked the daughters of women who participated in the Child Health and Development Studies
(CHDS) from 1959 to 1967. At that time, DDT was a widely used pesticide that
accumulated in the fat of animals, milk, butter, cheese and other products in
the food supply. It was also present in a number of products found in the home.
The CHDS research involved
20,754 pregnant women who gave birth to 9,300 daughters during that period. The
researchers used state records and a survey of CHDS participants’ grown
daughters to uncover how many had been diagnosed with breast cancer by the time
they turned 52.
To determine the levels of
DDT the daughters were exposed to in the womb, the research team analyzed
stored blood samples that were taken from their mothers during pregnancy or
shortly after they delivered their babies. During the 54-year follow-up period,
the researchers measured DDT levels in the mothers of 118 women who were
diagnosed with breast cancer and compared them to DDT levels in 354 women from
the group who did not develop breast cancer.
Cohn and her colleagues
found that elevated levels of DDT in the mother’s blood were associated with a
3.7 times higher
risk of breast cancer in their daughters, than those exposed to lower
levels. They also found the higher the level of DDT in a mother’s blood, the
more likely her daughter would be diagnosed with more advanced breast cancer.
The link to DDT remained
strong even after accounting for the mother’s breast cancer history. Among the
women diagnosed with breast cancer, 83 percent had the estrogen-receptor
positive form, where the cancer receives signals form the hormone estrogen to promote tumor
growth. Because DDT has been found to interfere with the production of
estrogen, this finding may explain the link.
Although the authors see
their study as the first to provide evidence of an association between DDT and
breast cancer, they acknowledge that it does not prove a cause-and-effect.
However, with the women most heavily exposed while in the womb in the 1960s currently
reaching the age of a heightened risk of breast cancer, the researchers see a
need for a new emphasis on finding and controlling environmental causes of
breast cancer that operates in utero.
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| Breast cancer risk tied to DDT varies by exposure timing |
“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,” Cohn said in the news release.
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