"With LDL cholesterol it's simple -- the lower the better," Heinecke said. "With HDL, it's much more complicated. The protein composition of people with and without heart disease is different."
So, measuring blood levels of LDL and HDL cholesterol is not as predictive of cardiac risk, as has been assumed, Heinecke stressed. "Protein composition [in HDL cholesterol] may be a better handle on whether someone is at risk," he added.
Animal studies have found "dysfunctional" HDL cholesterol, which works against coronary health, Heinecke said. "It is proposed that the same thing is going on in humans," he noted.
The finding of dysfunctional HDL proteins helps explain why a major pharmaceutical company ended work on an HDL-boosting drug when it was found to actually increase deaths and heart problems in a human trial.
A better understanding of the protein components of HDL could lead to more accurate tests for heart disease, Heinecke said. "Most people who have heart attacks have normal levels of HDL, so the composition of the HDL may tell who is vulnerable," he said.
Future cardiac therapy may include LDL-lowering statins and new drugs aimed at the damaging components of HDL cholesterol, Heinecke said.
There's more on HDL and LDL cholesterol at the American Heart Association.
SOURCES: Jay Heinecke, M.D., professor, medicine, University of Washington, Seattle; Aug. 22, 2007, American Chemical Society annual meeting, Boston
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