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.
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.