High Bone Mineral Density Associated With More Than a Doubling of Breast Cancer Risk

Long-term exposure to estrogen, as measured by bone mineral density,can more than double the risk of breast cancer, according to astudy led by researchers at the University of Pittsburgh and reportedin the November 5th issue of The Journal of the American MedicalAssociation. Estrogen replacement therapy is often prescribedin women during menopause to reduce hot flashes and other uncomfortablesymptoms of this transitional period.

According to the study, women with the highest bone mineral densityof the wrist bone, hip, or spine had more than twice the riskof breast cancer, as compared with women classified with the lowestmeasured bone mineral density.

"Ours is the first prospective study showing an associationbetween bone mineral density and subsequent breast cancer, linkingtwo of the most common and important conditions affecting a woman'shealth," said Jane Cauley, drph, associate professor of epidemiologyat the University of Pittsburgh's Graduate School of Public Healthand principal investigator of the study. "Identifying a commondenominator for these conditions, estrogen, should substantiallyimprove our understanding of their causes and treatments."

In the study group of 6,854 nonblack women age 65 or older, 97women developed breast cancer. The lowest rate of breast canceroccurred in women with low bone mineral density. Participantsin the 3-year study were evaluated at centers in Baltimore; Minneapolis;Monongahela, Pennsylvania; and Portland, Oregon.

Recent studies have shown that estrogen replacement therapy hasthe potential to reduce heart disease and increase bone mineraldensity. However, many breast cancers are known to grow in responseto estrogen, and most physicians do not recommend the therapyfor women with a history of breast cancer or those at high riskfor the disease.

Dr. Cauley also cautions in the study that "women with normalbone mineral density and with normal or high levels of estrogenthat is produced within the body could increase their risk ofbreast cancer if they take supplemental estrogen for the preventionof osteoporosis or cardiovascular disease."

Based on the results of this study, the risks and benefits ofestrogen replacement therapy need to be reevaluated with respectto bone mineral density, osteoporosis, breast cancer, and coronaryheart disease, according to the authors.

This study was supported by the National Institute of Arthritisand Musculoskeletal and Skin Diseases and the National Instituteon Aging.