HDL cholesterol is commonly called the "good" cholesterol, but new research suggests that it could be harmful to women going through menopause.

The new study finds that rather than helping to inhibit the formation of dangerous plaque in the arteries, HDL cholesterol may increase its buildup during menopause. This process is known as hardening of the arteries, or atherosclerosis, and can lead to heart trouble.

"This was surprising," said lead researcher Samar El Khoudary, an assistant professor of epidemiology at the University of Pittsburgh.

"We know that the good cholesterol is supposed to protect women," she said. And, before menopause, good cholesterol does help protect against heart disease, El Khoudary said.

But during menopause, HDL cholesterol seems to add to the plaque buildup, she explained. "This was independent of other factors such as body weight and levels of bad cholesterol," El Khoudary said.

The results of the study were presented earlier this month at the North American Menopause Society annual meeting in Las Vegas. Research presented at meetings is considered preliminary until published in a peer-reviewed journal.

For the study, El Khoudary and colleagues followed 225 women in their middle and late 40s for up to nine years. During that time, the women had the plaque in their arteries measured five times. All of the women were free of heart disease at the start of the study.

The researchers found that as the women went through menopause, increasing levels of good cholesterol were linked with greater plaque buildup. The findings suggest that the nature of HDL cholesterol may alter during menopause, making it ineffective in preventing plaque buildup, El Khoudary said.

It's not clear why good cholesterol may turn bad, she said. "There are many biological changes that happen to women during the menopausal transition," El Khoudary said.

Among these changes is the addition of fat to the abdomen and around the heart, she said. "This could put women in a state of chronic inflammation that could change the good cholesterol," El Khoudary suggested.

Whether the change in good cholesterol continues after menopause isn't known, and "more research is needed to really understand this process," she said.

Doctors need to keep track of risks linked to heart disease as a woman goes through menopause, El Khoudary said.

"Women need to strive for a healthy lifestyle. If they didn't do that before, it's really important now," she said.

Dr. Gregg Fonarow, a professor of cardiology at the University of California, Los Angeles, said the "relationship between HDL cholesterol levels, HDL function, and atherosclerosis progression is complex."

In certain circumstances, HDL can be inflammatory and increase hardening of the arteries, Fonarow said. "In other words, prior studies have shown that in certain patients or in certain circumstances, the good cholesterol can turn bad and actually promote the atherosclerosis," he said.

These findings may indicate that HDL function becomes altered during the transition to menopause, he said.

"Further studies are needed to evaluate HDL function in this and other patient populations to help develop additional strategies to prevent and treat atherosclerotic heart disease and stroke," Fonarow said.