CHICAGO -- Menopausal women using the common hormone supplements estrogen and progestin run a 20 percent higher risk of breast cancer than those who get estrogen alone, a study found.
While the risk of breast cancer is still low for women who take both hormones, the increased odds might further complicate the decision menopausal women must make about their health.
Estrogen is often prescribed to ease hot flashes and other menopause symptoms. It also has been shown to reduce the risk of heart disease and brittle bones.
After research in the 1980s linked estrogen use to uterine cancer, doctors began prescribing it along with progestin, a synthetic form of the hormone progesterone. It helps block estrogen's effect on the uterine lining.
Some previous studies have linked estrogen supplements, either alone or combined with progestin, with higher rates of breast cancer. Other research has found no increased risk.
Hormone-therapy proponents say the risks noted in the current study -- published in Wednesday's Journal of the American Medical Association -- were too small to be significant. Others contend the findings bolster the notion that women weighing hormone use should proceed with caution.
"If a woman is experiencing severe menopausal symptoms that affect her quality of life, fear of breast cancer shouldn't discourage short-term use," said Catherine Schairer, a National Cancer Institute epidemiologist and the study's lead author. With long-term use, she said, there is "considerably more concern."
The study gathered data on hormone use from questionnaires given to 46,355 women participating in a nationwide breast cancer screening project from 1980 through 1995. The survey identified 2,082 breast cancer cases.
Compared with women who reported never using hormones, women who used estrogen within the previous four years faced a 20 percent higher risk of breast cancer. For current or previous users of estrogen-progestin, the risk was 40 percent higher than for non-users.
For each year of use, the risk of developing breast cancer increased 1 percent for estrogen-only users and 8 percent for estrogen-progestin users.
Women who had been off either treatment for more than four years faced no increased risk, regardless of how long they had taken hormones.
Three Harvard University doctors, Walter Willett, Graham Colditz and Meir Stampfer, wrote an accompanying editorial urging further study of the long-term use of both hormones.
They said that the uncertainties raised by the new study and others suggest that long-term treatments other than estrogen and progestin be considered.
"The commonly held belief that aging routinely requires pharmacological management has unfortunately led to neglect of diet and lifestyle as the primary means to achieve healthy aging," they wrote. "Now is an appropriate time to reassess this emphasis."
Surveys by the North American Menopause Society show that about a third of U.S. women ages 45 to 65 -- some 16 million women -- use hormone supplements, either estrogen alone or combined with progestin.
Dr. Wolf Utian, executive director of the Menopause Society, said of the new study, "I'd have to see another one or two papers at least before I'd accept this as gospel."