Adding progesterone to estrogen in hormone replacement therapy appears to confer about the same protection against heart disease as estrogen alone, according to the first major study to examine combination therapy.

Looking at a total of 59,337 postmenopausal women over a period of up to 16 years in the ongoing Nurses Health Study, researchers from Brigham and Women's Hospital and Harvard Medical School in Boston found that women who took combination hormone therapy had 61 percent less chance of having a heart attack or dying from heart disease compared with those who did not use hormone replacement therapy.