WEDNESDAY, April 16 (HealthDay News) -- The timing of hormone therapy might determine its effect on a woman's heart.

Specifically, researchers have found that hormone replacement therapy (HRT) administered early in menopause to women with risk factors for heart disease did not diminish the function of the endothelial cells that line the inner walls of the arteries and might even improve it. Endothelial function is a way to measure early heart disease.

"Hormone therapy might not be as bad as was once thought," said Dr. Suzanne Steinbaum, director of Women and Heart Disease at Lenox Hill Hospital in New York City. "It might even be helpful in women with risk factors."

However, there isn't enough evidence to suggest that women should start taking HRT to lower their risk for heart disease, the authors emphasized.

The researchers, from Virginia Commonwealth University Medical Center in Richmond, presented their findings Wednesday at the American Heart Association's Arteriosclerosis, Thrombosis and Vascular Biology annual conference in Atlanta.

A section of the U.S. government-sponsored Women's Health Initiative (WHI), which was designed to look at health issues in postmenopausal women, was halted in 2002, when U.S. researchers found that hormone therapy led to an increased risk of adverse events that included heart attack, stroke, breast cancer and blood clots. The risk depended on whether the woman was taking estrogen alone or estrogen plus progestin, another female hormone.

Since that time, however, a more complex picture has emerged with various factors, including amount of hormone as well as timing, having an effect on risks and benefits of HRT.

Previous research indicated that HRT might have a negative effect on cardiovascular health in women who started therapy long after menopause, versus women taking it sooner after menopause.

Before the WHI, many women took HRT in the belief that it would reduce their risk for heart disease.

For this study, researchers used ultrasound to measure flow-mediated dilation (FMD) in the brachial artery in four groups of postmenopausal women (127 participants total).

FMD measures how well the endothelium functions. The brachial artery is the main artery in the arm.

"Endothelial dysfunction is often associated with risk factors," Steinbaum explained.

There were four groups in all: One comprised of women not on HRT, with no heart disease risk factors and about eight years postmenopausal; women not on HRT but who did have risk factors for coronary disease and a little over nine years postmenopausal; women taking estrogen alone, with risk factors and almost 12 years postmenopausal; and women taking estrogen plus progestin and 7.6 years postmenopausal.

Most women had started HRT about the time menopause started.

Women with risk factors who took HRT saw a slight improvement in FMD and, on the whole, there were no reductions in blood vessel function.

More information

Visit the Women's Health Initiative for more on hormone replacement therapy.