A compound created as the body processes cholesterol was to blame for giving scientists conflicting data about the effect of hormone replacement therapy in menopausal women, researchers say. Initial studies had found that estrogen helps keep the heart healthy, but a later study reported that women taking estrogen actually exhibited higher levels of coronary disease.
Now scientists believe the compound, known as 27HC, blocks estrogen from performing its beneficial functions to help keep blood vessels disease free. When 27HC levels are low and estrogen levels are normal—before menopause—estrogen protects the heart. But once estrogen levels drop in middle age, it could no longer deliver its benefits, even when introduced through replacement therapy.