Long-term exposure to estrogen, as measured by bone mineral density, can more than double the risk of breast cancer, according to a study led by researchers at the University of Pittsburgh and reported in the November 5th issue of The Journal of the American Medical Association. Estrogen replacement therapy is often prescribed in women during menopause to reduce hot flashes and other uncomfortable symptoms of this transitional period.
According to the study, women with the highest bone mineral density of the wrist bone, hip, or spine had more than twice the risk of breast cancer, as compared with women classified with the lowest measured bone mineral density.
"Ours is the first prospective study showing an association between bone mineral density and subsequent breast cancer, linking two of the most common and important conditions affecting a woman's health," said Jane Cauley, drph, associate professor of epidemiology at the University of Pittsburgh's Graduate School of Public Health and principal investigator of the study. "Identifying a common denominator for these conditions, estrogen, should substantially improve our understanding of their causes and treatments."
In the study group of 6,854 nonblack women age 65 or older, 97 women developed breast cancer. The lowest rate of breast cancer occurred in women with low bone mineral density. Participants in the 3-year study were evaluated at centers in Baltimore; Minneapolis; Monongahela, Pennsylvania; and Portland, Oregon.
Recent studies have shown that estrogen replacement therapy has the potential to reduce heart disease and increase bone mineral density. However, many breast cancers are known to grow in response to estrogen, and most physicians do not recommend the therapy for women with a history of breast cancer or those at high risk for the disease.
Dr. Cauley also cautions in the study that "women with normal bone mineral density and with normal or high levels of estrogen that is produced within the body could increase their risk of breast cancer if they take supplemental estrogen for the prevention of osteoporosis or cardiovascular disease."
Based on the results of this study, the risks and benefits of estrogen replacement therapy need to be reevaluated with respect to bone mineral density, osteoporosis, breast cancer, and coronary heart disease, according to the authors.
This study was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases and the National Institute on Aging.