One benefit that was seen during the treatment phase of the trial -- a reduced risk of hip fractures -- didn't persist when the women stopped taking estrogen.
The benefit that did seem to last, however, was a decreased risk of breast cancer. Over the entire follow-up period, the incidence of breast cancer was 0.27 percent in women who took estrogen, and 0.35 percent in women who took the placebo.
LaCroix said it's unclear what the mechanism behind the apparent protection against breast cancer is. Normally, estrogen is implicated in the development of breast cancer, not in the prevention of the disease.
She said this aspect of the study definitely needs more research, but added of this finding, "It's reassuring, if you're a woman in your 50s who has menopausal symptoms and a reason for taking estrogen."
Dr. Graham Colditz, co-author of an accompanying editorial in the same issue of the journal and chief of the division of public health sciences at the Washington University School of Medicine in St. Louis, said the reduction in breast cancer may be because these women were already past menopause when the estrogen was given. "There's an involution of breast cells after menopause, so there would appear to be fewer bad actors waiting to respond to the hormones," he said.
The study also found that the use of estrogen produced better outcomes for younger women than for women in their 70s. Heart disease risk, colorectal cancer risk and the overall risk of dying were lower in women in their 50s compared to those in their 70s, according to the study. <
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