Lead researcher MaryFran Sowers of the University of Michigan School of Public Health showed that in women without existing atherosclerosis, hormone therapy use included some positive effects on lipids but also some negative effects related to heart health.

Sowers said the timing hypothesis suggests that if a woman implements a hormone therapy program within six years of her final menstrual period, this narrow window is enough to deter heart disease from developing with the onset of menopause. But the study findings suggest that explanation isn't quite so simple, Sowers said.

Sowers said the research shows it's critical for women considering hormone therapy to discuss their heart health with their doctor.

"If the woman walks into the doctor's office with a certain degree of heart disease burden already, then she and her healthcare provider may decide that hormone therapy adds too much to the burden," Sowers said in a statement. "If she doesn't have that burden, they may decide that hormone therapy is an acceptable burden."