While unopposed conjugated equine estrogen (CEE) confers no protection against myocardial infarction (MI) or coronary death in generally healthy postmenopausal women between ages 50 and 79, when researchers looked only at women between 50 and 59, the story changed.

The findings come from the Women's Health Initiative and analysis of data on over 10,000 women aged 50 to 79 who had previously undergone hysterectomy. The women took either CEE 0.625 mg/d or placebo for approximately 7 years. During that time, 201 coronary events occurred in the group of women taking estrogen and 217 occurred in the group taking placebo (hazard ratio [HR] 0.95; nominal 95% confidence interval [CI], 0.79–1.16).

But when the researchers looked only at women aged 50 to 59, they found the HR for MI or coronary death in the group taking estrogen versus the group taking placebo to be 0.63 (nominal 95% CI; 0.36–1.08). They also found less frequent coronary revascularization (HR 0.55, nominal 95% CI; 0.35–0.86). But the low overall event rate in these younger women mandates that additional studies be conducted to determine whether any true protective benefit exists, according to the investigators.

Hsia J, Langer RD, Manson JE, et al. Conjugated Equine Estrogens and Coronary Heart Disease: The women's Health Initiative. Arch Intern Med. 2006;166:357-365.