Despite these concerns, most physicians still feel the benefits of ERT outweigh the risks. That is because they believe that taking estrogen reduces the risk of heart disease, one of the most common causes of death and disability among older women. Doctors base that belief on a series of studies showing that women who take estrogen have 35-45% fewer cases of heart disease than women who do not take the hormone.

    Unfortunately, however, those studies do not prove anything. It is well known that women who take estrogen also eat healthier food, exercise more often, go to the doctor more frequently for checkups, are more intelligent, have higher incomes, and generally take better care of themselves than do non-users of estrogen. It is quite possible that the reduction in heart disease risk associated with ERT is due to one or more of these other factors and has nothing to do with the estrogen therapy.
    Only a so-called "prospective" study, in which women are randomly assigned to receive ERT or a placebo, can provide a definitive answer. Such a study is now in progress and preliminary results have just been published. In that study, 875 healthy postmenopausal women were given either a placebo or one of four estrogen regimens. After three years, women receiving ERT had more favorable cholesterol values (the "bad" LDL-cholesterol was 20% lower and the "good" HDL-cholesterol was higher) than the women given the placebo.
    This report was widely circulated in the media and touted as the first real "proof" that ERT prevents heart attacks. However, a careful reading of the original study reveals that conclusion to be premature and possibly incorrect. The medical literature is replete with studies of drugs that lowered cholesterol levels, but did not prevent heart disease. The same may be true for postmenopausal estrogen therapy. In the study cited above, five new cases of heart disease developed during the first three years. All of these cases occurred in the ERT group and none among those receiving the placebo. Even considering the fact that there were more women receiving ERT (701) than placebo (174), these results are not even remotely encouraging. In fact, a statistical analysis of the data reveals there is a 71% probability that giving estrogen to postmenopausal women actually causes heart disease. While some people may take comfort in improved cholesterol values, most women, if forced to choose, would pick a healthy heart over a "healthy" lab test.
    Another finding from the study was also cause for concern. During the first three years, ten women developed blood clots, four of which were serious. All ten blood-clot episodes occurred in women receiving estrogen and none in the placebo group.