Heart Disease - Hormone Therapy And Disease: Menopause
Content provided by the Faculty of the Harvard Medical School
Heart disease
Besides relieving menopausal symptoms, one major reason for using hormone therapy in the 1990s was the belief that it protected against heart disease. Over the years, a number of large studies revealed that estrogen lowers total blood cholesterol and harmful LDL cholesterol, while increasing beneficial HDL cholesterol. That's good, because high LDL cholesterol is a major risk factor for heart disease, and HDL is protective. Studies published in the 1980s and early 1990s that surveyed large groups of women showed that women using combined hormone therapy had a 40% lower risk of heart disease than women who didn't use it. These findings, from the long-term Nurses' Health Study among others, contributed to millions of American women receiving prescriptions for hormone therapy in the belief that it could prevent heart disease.
That notion changed when findings from the Heart and Estrogen/Progestin Replacement Study (HERS) appeared in 1998. This was the first large randomized placebo-controlled clinical trial of hormone replacement therapy in women with heart disease. After four years, the results showed no difference in the number of heart attacks or strokes between randomly chosen women who took Prempro and those who did not. In fact, HERS showed that postmenopausal hormones raised the risk of heart disease and blood clots during the first year or two that women took them. Even more recent, short-term data from the Nurses' Health Study show the same pattern. It's important to note that most of the heart-related problems occurred within the first two years of using the combined hormone therapy. So, why did the earlier Nurses' Health Study data show that taking hormones reduced heart disease? One reason may be that the women who were taking hormones were healthier to begin with.
The age at which a woman begins hormone therapy may also make a difference. For example, the WHI results that showed an increase in heart attacks for women taking combined hormone therapy included mainly older women with an average age of 64 — about a decade past menopause. At that age, women are more likely to have clogged arteries and are therefore more likely to have a heart attack. But the Nurses' Health Study looked at women who started hormone use at or soon after menopause. It's possible, as some experts believe, that hormones may be beneficial in early menopause and harmful when started late after menopause.
Several studies seeking to untangle these distinctions are currently under way, including a five-year, multicenter trial privately funded by the Kronos Longevity Research Institute. Researchers are testing whether hormone therapy prevents the progression of atherosclerosis in women ages 42–58. Women in the study will take either a placebo or a transdermal patch or pill that contains estrogen plus progestogen.
| How risky is it? When the Women's Health Initiative says hormone replacement therapy raises the risk of breast cancer by 26% and heart attack by 29%, it sounds like a lot. But what does that mean for you? It's important to recognize that two types of risk are evaluated in health research. Medical studies generally report on what is known as relative risk. That's a comparison of one group to another (in this case, women taking hormone therapy and women taking placebo pills). Researchers want to know the chances that one group will develop a disease compared with the other group. But relative risk is dependent on absolute risk. Absolute risk is the total number of people who get a disease during a specified time period — say, 5 in 1,000 over 5 years. So if there are very few total cases of a disease to begin with, then an increase (relative risk) of 26% doesn't affect many women. In the case of the Women's Health Initiative, researchers felt that although the absolute risk was not high, it was high enough to cancel the study to avoid putting more women at risk of getting breast cancer and heart disease. In that study, combined hormone therapy raised breast cancer risk by 26% — that's the relative risk. In absolute terms, that means only 8 more breast cancers among every 10,000 women who take hormones compared with those who don't. The 29% increase in heart attacks translates to only 7 more heart attacks among 10,000 women. If you look at a study in a medical journal, you'll see that relative risk usually is expressed in ratios that compare the outcomes of the two groups in a study. The number 1 is the starting point. If the ratio is 1.0, that's even odds — no difference between the groups being studied. If the ratio is greater than 1.0 — say, 1.6 — then those who took the drug being studied had a 60% greater risk of developing the illness. If it's below 1.0 — say, 0.8 — then those who took the drug had a 20% lower risk of developing the disease than those who didn't. It's important, too, to recognize the effects of risk over time. Consider again the findings about increased breast cancer risk linked with hormone therapy. If a woman takes hormones for one year and has a low risk of breast cancer to begin with, the increase may not cause great harm. But if a woman at high risk takes estrogen and progestogen for 10 years, she could be increasing her risk for breast cancer to an unacceptable level. Knowing how to apply health research to your own risk for illness is a powerful way to help ensure a lifetime of good health. |
| Last updated: | August 13, 2007 |
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Medical content reviewed by the Faculty of the Harvard Medical School. Harvard Health Publications, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved. Used with permission of StayWell.
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