LONDON (AP) -- The debate over the possible health risks of chemicals that mimic the hormone estrogen has flared again with a new study suggesting that exposure to a long-banned pesticide increases the risk of breast cancer.
Women with the highest traces of the pesticide Dieldrin in their blood were twice as likely as women with the lowest levels to develop breast cancer, Danish researchers found. Their findings were published in The Lancet, a British medical journal.Chemicals like Dieldrin are thought to mimic the effects of estrogen, which promotes tumor growth in breast cancer. Although Dieldrin and other chemicals of its type, such as DDT and PCBs, have been banned in the United States and Europe for several years, they remain in the environment and accumulate in the body.
"This is very interesting new data. It reopens the door to this field," Dr. Mary S. Wolff of Mount Sinai Medical Center in New York said of the study, from the Center for Preventive Medicine in Glostrup, Denmark.
"We had so many negative studies (that did not show a link) that people put this issue to rest."
But while the latest findings will reignite the debate, researchers caution that evidence is mixed.
Some small studies have shown a link between breast cancer and these types of pesticides, yet about as many other studies -- including two big ones -- have demonstrated no correlation.
The latest study is as large as the biggest studies to date, involving 7,712 women monitored for 19 years.
Blood samples were taken from women in 1976 to check for levels of 48 pesticides. In 1996, the scientists retested 240 women who had developed breast cancer and 477 women who had not.
"The more exposure, the more the risk," said Dr. Annette Hoyer, lead researcher in the study.