In the 1990s, it was good. In 2002, it was bad. In December of last year, researchers seemed to have confirmed that it was responsible for millions of cases of breast cancer.
Now, in a new study, researchers say that hormone replacement therapy, or HRT, may actually be good after all -- but only for younger women.
Researchers found that for women aged 50-59 who had undergone hysterectomies, taking estrogen actually decreased the buildup of plaque in their coronary arteries, which is a predictor of future heart problems.
Most younger women taking HRT do so to reduce menopausal symptoms such as hot flashes and night sweats.
"[This study] adds to the mounting evidence providing reassurance for recently menopausal women," said the study's lead author and chief of the Division of Preventative Medicine at Brigham and Women's Hospital, Dr. JoAnn E. Manson.
"Younger, recently menopausal women need as much information as possible to make informed choices about their health. This information can be added to the equation to help women weigh the benefits and risks of treatment."
The study evaluated the hearts of 1,064 women after eight years of taking either estrogen therapy or a placebo. Women who received estrogen were 30-40 percent less likely to have severe amounts of calcium plaque in their coronary arteries than those who received the placebo.
Those women who were the most diligent about taking their estrogen, following through with their treatment at least 80 percent of the time, had an even greater reduction -- 60 percent -- in the amount of calcium in their arteries.
The study was carried out by the Women's Health Initiative, the group that originally researched the risks of hormone replacement therapy, and was funded by the National Institutes of Health.
"This study emphasizes the need to consider all the research on hormone therapy and the traits of each individual patient before making a decision about its use," said Dr. Robert Rebar, executive director of the American Society for Reproductive Medicine.
Estrogen Therapy Uncertainties
The recommendations for HRT seem to change every few years. In the 1990s, millions of women began taking hormones when association studies suggested they were good for heart health.
Then the Women's Health Initiative released its initial findings in 2002 linking estrogen therapy to a number of serious health problems such as breast cancer, heart disease and stroke, and many women stopped taking the hormone.
The WHI pulled the plug on its studies of estrogen therapy in 2004 due to elevated risk of stroke. The study that examined the effects of estrogen plus progestin, a treatment normally used in women who have intact reproductive organs, was halted in 2002 due to an increased risk of breast cancer.
When they were looking at the data for younger women, within a few years of menopause, though, the researchers began to notice a trend of fewer heart attacks.
So they decided to do a sub-study for women ages 50 to 59 who had had hysterectomies. And they found an overall reduction in the amount of calcified plaque buildup in those women who took estrogen.
Now, armed with the results of this new sub-study, many experts are urging a balanced approach.
"The rush to pronounce harm or benefit for all patients on the basis of a single study is unwarranted -- and dangerous," said Rebar. "We are clearly learning that the benefits of estrogen in young, healthy, symptomatic, postmenopausal women outweigh the risks."
Timing Is Key
Researchers suggest that timing for hormone replacement therapy may be the key to managing risk while alleviating menopausal symptoms.
Many experts agree that women who take estrogen at or soon after menopause may experience the greatest benefits. But women who start hormone therapy later, long after menopause, may have more risks than advantages.
"There are analogies for early benefit and late harm," said Michelle Warren, medical director of the Center for Menopause, Hormonal Disorders and Women's Health at Columbia University. "If I take a woman who has never exercised, and make her exercise at age 63, I can kill her. There is an analogy here."
Some Cite Flaws
"This study was done in women who had hysterectomies and who took estrogen only," said Stacie Geller, director of the National Center of Excellence in Women's Health. "Although this is mentioned briefly, these findings do not translate to women with an intact uterus who must use estrogen plus progestin."
The researchers maintain that there is more work to be done to explain the relationship between hormone therapy and heart health.
Study author Manson noted that since the research only looked at women who had already had hysterectomies, the findings may not apply to younger women across the board.
In addition, some doctors think that it may be difficult to establish a strong link between calcium plaques in the arteries and heart health.
Dr. Brian Walsh, of Brigham and Women's Hospital, said, "Coronary calcium is a surrogate marker for cardiovascular disease, which is not as good as a hard endpoint like cardiovascular event or death."
There are two large clinical studies currently under way to examine the effects of combination therapy on the heart health of younger postmenopausal women.
Allaying Estrogen Anxiety
Most doctors still agree that hormone therapy should be taken at the smallest dose and for the shortest time possible.
Some say that the WHI findings in 2002 sent the wrong message to women.
"Instead of clearly recognizing that they were reporting on older women, they extrapolated that data to all peri- and early menopausal women, advising them in essence to get off their hormones as soon as possible," said Dr. Wulf Utian, executive director of the North American Menopause Society.
"Now there are millions of women who are several years beyond menopause, off hormones, who could have been protected, but are not. Indeed, they cannot even contemplate starting again, because they are now in the older group and the potential danger zone."
Researchers are continuing to look for new answers to help women and maintain their safety, and the course of action seems to be adjusting constantly.
As Dr. Howard Hodis, director of the Artherosclerosis Research Unit at the University of Southern California, noted, "The mantra five years ago was: no more hormones for any women ever again, and look where we are today. It's an evolving process."