Hormone Therapy and Heart Disease in Women

Medical Author Revision: Dennis Lee, M.D.
Medical Editor: Carolyn Janet Crandall, MD, MS, FACP

After menopause, the production of estrogen by the ovaries gradually diminishes over several years. Along with this reduction, there is an increase in LDL ("bad" cholesterol) and a small decrease in HDL ("good" cholesterol). These changes in lipid levels are believed to be one of the reasons for the increased risks of developing coronary heart disease (CHD) after menopause. Women who have had their ovaries surgically removed (oophorectomy) or experience an early menopause also have an accelerated risk of CHD.

Since treatment with estrogen hormone results in higher HDL and lower LDL cholesterol levels, doctors thought for many years that estrogen would protect women against CHD (as well as protect against dementia and stroke). Many studies have found that postmenopausal women who take estrogen have lower CHD rates than women who do not. Unfortunately, many of these studies were observational (studies in which women are followed over time but decide on their own whether or not they wish to take estrogen). Observational studies have serious shortcomings because they are subject to selection bias. For example, women who choose to take estrogen hormones may be healthier and have a lower risk of heart attacks than those who do not. In other words, something else in the daily habits of women who take estrogen (such as exercise or a healthier diet) may make them less likely to develop heart attacks. Therefore, only a randomized, double-blind, placebo-controlled trial (a study in which women agree to be assigned to estrogen or a placebo or sugar pill at random but are not told which pills they took until the end of the study) can establish whether hormone therapy after menopause can prevent CHD.