MidLife
Results of the HERS study
The results of HERS are surprising in light of previous observational studies, which found lower rates of CHD in women who take postmenopausal estrogen. Although observational studies cannot provide conclusive answers about a particular treatment since the groups studied can differ in significant ways, they provide important clues and the unexpected null finding in HERS is worthy of analysis.
The authors speculate that the HERS results may be explained by differences in the effect of therapy over time. When they examined the results by year, they found that there was a trend towards a higher risk for CHD "events" such as heart attack during the first year of therapy but that this trend was reversed during the final two years. By the end of the study, there was no significant difference in CHD risk between the two groups.
One possible explanation for the early increase in CHD events could be due to negative effects of treatment on clot formation. The authors suggest that over time these negative effects were gradually outweighed by a longer-term positive effect on the progression of atherosclerosis that was caused by the favorable cholesterol changes. In previous studies in which cholesterol-lowering drugs have produced a favorable effect on lipoproteins, there is usually a 1- to 2- year delay before CHD risk is reduced. Many of the women in the HERS study may not have been on treatment long enough for the positive cholesterol-lowering effects of HRT to reduce the risk of CHD.
Despite this explanation, the HERS investigators conclude that until results from other ongoing randomized trials of HRT are available, estrogen plus progestin should not be started in women with CHD to prevent heart attacks.
Source: The National Heart, Lung and Blood Institute
