CHAPEL HILL -- U.S. women who live on farms are less likely to develop breast cancer than other women, a new University of North Carolina at Chapel Hill study shows. Pesticide exposure among farm women appears to reduce the protective effects of such work, however, and boosts their breast cancer risk slightly, researchers say.
"We found that farming overall is protective against breast cancer when compared with the general population," said Dr. Eric Duell, a former doctoral student at the UNC-CH School of Public Health. "It's nice to find that maybe there's something out there that is actually decreasing women's breast cancer risk."
A report on the detailed study -- the first of its kind among farm women -- appears in the September issue of the journal Epidemiology. Besides Duell, now a fellow at Harvard University, UNC-CH authors are Dr. Robert Millikan, assistant professor of epidemiology; Dr. David Savitz, professor and chair of epidemiology; programming assistant Joanna Smith and Dr. Michael Schell, research associate professor at the UNC Lineberger Comprehensive Cancer Center.
Researchers investigated 862 cases of breast cancer among women living in 24 eastern and central N.C. counties and compared them with 790 women without breast cancer who lived in the same areas, Duell said. About half the women, who ranged in age from 20 to 74, were black.
Detailed health and work histories, including information on all farm work since age 7, crops and livestock grown and pesticides used, were available. That's because all subjects are participating in UNC-CH's larger ongoing Carolina Breast Cancer Study.
Overall, women who had farmed more than 23 years had about a 40 percent lower risk of breast cancer than women who had never lived on farms, the scientists found. Those who farmed longer were better protected, analyses showed, while those with less agricultural experience were less protected.
"We should continue to study this group of farm women to try to find what it is that puts them at lower risk," Duell said.
Some pesticides such as DDT, banned in the United States in 1972, can still be measured in people almost 30 years later, he said. A concern has been that DDT and certain other pesticides can mimic the effects of the female hormone estrogen and may promote breast cancer.
Even during years when DDT was in use, from 1945 to 1972, scientists still found a protective effect for farming depending on the number of years worked, Duell said. Age, crops produced and livestock handled made no difference.
Factors that may be important are that farm women tend to bear children earlier and have more, he said. They reach puberty somewhat later and enter menopause earlier. Also, they tend to smoke and drink alcohol less than others. Controlling statistically for those behaviors and characteristics, however, did not eliminate the protective effect of farm work. The group could not determine the effect of physical activity, which some scientists think reduces the chance of breast cancer.
"This is the first population-based case controlled study to look at a spectrum of pesticides used in agriculture, and for that reason, we think it is a fairly significant addition to the scientific literature," Savitz said. "For breast cancer, just as for a lot of other illnesses like cardiovascular disease, living on a farm generally seems to be good for people. We don't fully understand the reasons."
Among women living on farms, however, pesticides appear to boost the risk slightly, although the increased risk does not exceed that of women not living on farms, he said.
"Obviously we've known for a long time that pesticides are bad for you, but this work provides additional encouragement to minimize exposure," Savitz said.
Drs. Beth Newman, formerly at UNC-CH and now at Queensland University of Technology, and Dale Sandler of the National Institute of Environmental Health Sciences, also participated in the study, which NIEHS, the National Cancer Institute and the UNC Lineberger Comprehensive Cancer Center supported.
Note: Duell can be reached at (617) 432-4677, Savitz at (919) 966-7427 and Millikan at 966-7437. Also, eduell@hsph.harvard.edu, david_savitz@unc.edu and bob_millikan@unc.edu.
By DAVID WILLIAMSON
UNC-CH News Services
Journal
Epidemiology