Several larger, earlier studies found no evidence that DDT caused breast cancer. The largest, a 2002 study involving more than 3,000 women in Long Island, N.Y., concluded that the breast cancer rate did not rise with increasing DDT levels in their blood. To some, that seemed to put the question to rest.
However, those studies were based on amounts found in the blood of middle-age and older women, after they had contracted cancer and decades after DDT was banned.
For The Record
Los Angeles Times Thursday, October 04, 2007 Home Edition Main News Part A Page 2 National Desk 1 inches; 51 words Type of Material: Correction
DDT and cancer: An article in Sunday's Section A about the link between DDT and breast cancer identified the researchers as coming from UC Berkeley's Child Health and Development Studies. The project was part of the university until 1986 but is now administered by the nonprofit Public Health Institute in Berkeley.
The new study looked for the first time at DDT concentrations in women when they were primarily in their 20s, closer to when their breasts developed and during a time of widespread spraying. The UC Berkeley team measured DDT in blood collected between 1959 and 1967 from 129 women who had just given birth in Kaiser Permanente hospitals in the Oakland area.
Their study, funded by the National Cancer Institute, will be published Monday in the October edition of the journal Environmental Health Perspectives.
The women in the top third of DDT concentrations who were exposed before age 14 were five times as likely to get breast cancer as the women with the lowest levels, according to the study. No relationship between cancer and the insecticide was found in the women born before 1931, who would have been older during any exposure.
The Berkeley study "is very compelling and important and addresses a question about timing of exposure that many of the existing studies could not address," said Mary Beth B. Terry, an associate professor of epidemiology at Columbia University's Mailman School of Public Health. She co-wrote the Long Island study.
"Their findings in general support their hypothesis that the earlier you were exposed, the stronger the effect," Terry said. "We think with organochlorines and other exposures, the timing may be more important in terms of breast cancer."
Scientists said the study was particularly important because the blood was drawn when DDT was still heavily used, so it offered a snapshot of women with levels an order of magnitude higher than today.
"It really turns back the clock in a very unique way," said Steven Stellman, a professor of clinical epidemiology at Columbia University who has studied DDT and breast cancer.
A fivefold increase in breast cancer -- 400% -- is considered very high. Most traditional risk factors, such as late menopause, obesity and older age at first pregnancy, increase risk by 50% to 100%.
