Participants whose HDL cholesterol was less able to remove cholesterol from the macrophages tended to have a thicker carotid artery.
"The function of the HDL was an even better predictor of the thickness of the carotid wall than the HDL level itself," said Rader, the senior study author. The researchers term this function "cholesterol efflux capacity."
The study is published in the Jan. 13 issue of the New England Journal of Medicine.
In a second experiment, the researchers measured the HDL function of 442 people who had undergone bypass surgery due to a blocked artery and 351 people without heart disease.
Those with heart disease had poorer HDL function than those without it, even after adjusting for traditional risk factors, the investigators found.
"We found the people who had blockages had significantly less ability to promote cholesterol removal than those who had no blockages," Rader said. "The measure of HDL function was a much better predictor of the likelihood of having blocked arteries than the measure of HDL cholesterol itself."
That doesn't mean high HDL is of no help, noted Dr. Robert Eckel, past president of the American Heart Association and a professor of medicine at University of Colorado. Generally, people with higher levels of HDL also have better function, Eckel said.
But the findings may help explain why some people with high HDL are still found to have heart disease.
"I see plenty of people who have heart disease but who also have high levels of HDL. So what is going on there? Why aren't they protected? This study may suggest their HDL isn't working properly to carry out its function," Eckel said.
The converse may also be true: even someone with low levels of HDL may never develop heart disease because their HDL may work very well.
"Just because someone's HDL level was hig
All rights reserved