The benefits and risks of hormone replacement therapy: an epidemiologic overview

In postmenopausal women estrogens alone are effective in reversing vasomotor symptoms and vaginal atrophy. They also prevent the bone loss associated with osteoporosis and reduce the risk of cardiovascular disease, probably through their beneficial effects on lipid metabolism. Unopposed long-term estrogen therapy, however, increases the risk of developing endometrial hyperplasia, endometrial cancer, and possibly breast cancer as well. The risk of developing endometrial cancer can be reduced by combining a progestin with the estrogen, by controlling obesity, and by rigorous clinical screening and surveillance. The effect of progestins on the risk of developing breast cancer is still controversial. Although some progestins may reverse the cardioprotective effect of estrogens, those with minimal androgenicity appear less likely to do so. Hormone replacement therapy that combines estrogen with a progestin of minimal androgenicity is thus a rational alternative to unopposed estrogen therapy. Current epidemiologic knowledge suggests that the benefits of hormone replacement therapy, with or without any progestins, strongly outweigh the risks.