Effects of Estrogen plus Progestin on Stroke in the Women’s Health Initiative

May 2003

Findings Summary

While the world continues to discuss the July 2002 findings from the WHI Estrogen Plus Progestin Study, WHI investigators are busy analyzing the data in much more detail. Study findings on the risk of stroke in women taking combined estrogen plus progestin (E+P) were published in the May 28, 2003 issue of the Journal of the American Medical Association (JAMA). These updated results include data on additional strokes, information on types of stroke, and data on risk factors for stroke. As reported earlier, women taking active E+P developed more strokes than did those taking placebo (inactive) pills. This updated analysis showed that after an average of 5.6 years, 151 (1.8%) of the 8506 women on estrogen plus progestin and 107 (1.3%) of the 8102 women on placebo developed strokes. We can describe these same findings in several other ways:
  • For every 10,000 women followed for 1 year, we would expect to see 31 strokes in women on E+P compared to 24 in women on placebo.
  • The excess risk of stroke due to E+P was 7 strokes for every 10,000 women over one year.
  • There is a 31% increase in the risk for stroke due to E+P.
Most of these strokes were caused by blood clots in the brain. This is the type of stroke affected by E+P. The less common type of stroke, caused by bleeding into the brain, did not seem to be affected by E+P.
The increased risk of stroke due to E+P was seen in all groups of women studied, including those closest to the menopausal change and those with symptoms like hot flashes. The authors conclude that combined E+P should not be used to prevent cardiovascular diseases.
The authors confirmed several risk factors for stroke that women can control: high blood pressure, smoking, and diabetes. They also suggest that exercise and taking vitamin C supplements reduce risk for stroke. Although the health benefits of exercise have been generally accepted, the benefits of vitamin C in reducing stroke risk will need to be confirmed by other randomized clinical trials.
Further work is being done within WHI to learn more about the ways in which E+P affects cardiovascular disease.