Harvard Health Letter

Hormone therapy and heart disease: Is it all in the timing?

Two trials will test whether there is an "age effect" for hormone therapy.

For years, doctors believed estrogen was the key to protecting older women against heart disease. It started with a basic observation: Heart disease is rare for women before menopause, when estrogen levels are high, but becomes much more common after menopause, when they fall. Findings from long-term observational studies like the Nurses' Health Study added credence to the idea. They showed that women who took hormones after menopause had markedly lower rates of heart disease. In addition, many women said they just felt a whole lot better when they were on postmenopausal hormone therapy. The number of prescriptions soared.

Hormones prove risky

Then in July 2002, came the results from the Women's Health Initiative (WHI), a randomized controlled trial of hormone therapy. They showed a higher rate of heart disease among women using hormones. Because randomized controlled trials like the WHI are considered to provide stronger evidence than observational studies like the Nurses' Health Study, many doctors concluded that the results of the WHI trumped findings from the observational studies. Since heart disease is by far the most common cause of death in women, any protective effects of hormone therapy against osteoporosis or (possibly) colon cancer were small next to the apparently negative effects on heart disease. Use of hormone therapy plummeted.

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