Until now, what to do with "good" cholesterol, or HDL, and "bad" cholesterol, or LDL, has been relatively straightforward.

"If LDL is high, lower it, and if HDL is low, raise it," said Dr. Perry Weinstock, chief of cardiology at Cooper University Hospital.

The correlation between high HDL levels and lowered risk for heart disease is so strong, it has long been thought to be a causal relationship.

HDL is thought to travel through arteries and capture cholesterol trapped there, then transport it to the liver where it then passes out of the body.

But a new genetic analysis brings the role of HDL into question.

Ben Voight, a statistical geneticist at the University of Pennsylvania, is co-lead author of a study published in the Thursday online edition of the medical journal The Lancet.

"We studied 15 genetic variants that are known to increase the 'good' cholesterol in about 100,000 people," Voight said. "And what we found was that variants that increase HDL are not associated with decreased risk of heart attack."

The findings suggest good cholesterol could be an indicator of other, yet unknown factors that actually do protect the heart, factors perhaps controlled by the same genes.

"It certainly challenges the conventional wisdom and makes us much more concerned that maybe we're still missing some details here," Weinstock said.

The study does not challenge the idea that being born with high levels of good cholesterol means you are less likely to get heart disease. But it does bring into question whether trying to raise HDL artificially with supplements such as niacin does any good.

And the early research does not bode well for makers of some HDL-boosting drugs currently in the drug production pipeline.