Older studies have shown that estrogen plus progesterone increases breast risk, but until now there has been little research on what effect testosterone has on such risk. While considered the male sex hormone, women, too, have testosterone and as they age, their natural levels decline.
Some evidence suggests that many of the symptoms of menopause -- including decreased sex drive, worse moods, and poorer quality of life -- may be related to a decline in testosterone. And the use of testosterone as part of hormone replacement therapy appears to be on the rise. The number of women in the study who used estrogen-plus-testosterone therapy increased dramatically from 33 in 1988 to 550 in 1998.
Long-Term Effects of Hormone Therapy
In the new study, in the July 24 issue of the Archives of Internal Medicine, researchers led by Rulla M. Tamimi, ScD, of Brigham and Women's Hospital and Harvard Medical School in Boston, and colleagues studied the long-term effects of estrogen-plus-testosterone therapy in 121,700 women who were part of the Nurses' Health Study. The women completed an initial questionnaire and follow-up surveys every two years that included questions about menopausal status, medical conditions, and the use of hormone therapy.
There were 4,610 cases of breast cancer among postmenopausal women during 24 years of follow-up. Women who were currently taking estrogen plus testosterone had a 77% higher risk of developing breast cancer than those who had never used hormone therapy. By contrast, women currently using estrogen showed a 15% increased risk of breast cancer and those who were taking estrogen plus progesterone had a 58% increased risk of breast cancer.
What's more, women who had gone through menopause naturally and took estrogen plus testosterone had 2.5 times the risk of breast cancer than those who had never used hormone therapy. Estrogen-only therapy showed a 23% increased risk and estrogen-plus-progesterone therapy was linked to a 66% increased risk in those women with natural menopause.
Exactly how testosterone may increase the risk of breast cancer is not fully understood, but researchers speculate that enzymes in the breast tissue may convert testosterone to estradiol, an estrogen-like hormone that may contribute to the development of breast cancer.
Risks vs. Benefits
So what's a woman to do?
"Given the substantial evidence implicating combined estrogen plus progestin therapy in and the results of the present study regarding estrogen plus testosterone therapy, women and their physicians should reconsider use and, more specifically, long-term use of these therapies," the researchers conclude. "Although postmenopausal therapies may provide improvement with respect to sexual functioning, general well-being, and bone health, the increased risk of breast may outweigh these benefits."
When it comes to treating the symptoms of , "'safe' is a relative term," says Donnica Moore, MD, a women's health expert based in Far Hills, N.J. "There is no product -- prescription or over-the-counter (OTC) -- that works that is absolutely free of side effects. And there are also risks, per se, of not treating symptoms," Moore says. "There is no one-size-fits-all answer for all women. Each woman with menopausal symptoms or concerns should speak with her doctor, who is in the best position to help her decide what's best for her given her unique circumstances, her symptoms, her risks, and her medical history."
The use of testosterone as part of a hormone replacement therapy may continue to increase, Moore predicts. "This is in large part due to increased awareness of the benefits of testosterone for women with decreased libido," she tells WebMD.
"Women should not take any OTC or pharmaceutically created testosterone that isn't prescribed by their doctor -- and your doctor knows your specific risks," says Lila E. Nachtigall, MD, a reproductive endocrinologist and director of the Women's Wellness program at New York University School of Medicine in New York City. Nachtigall is also the author of several books including Estrogen.
"The bottom line is that women must discuss their own risks and benefits with their doctor."