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