A day after a study in the journal Lancet challenged the long-standing notion that raising levels of HDL -- commonly known as "good" cholesterol -- prevents heart attacks, top cardiology experts differed on whether the research really means the end of the road for therapies aimed at boosting HDL levels to beat back heart disease.
Some, like Dr. Philip Greenland, said the new evidence may very well close the book on such efforts.
"After several blows to the head of this theory, it is on the ropes, or maybe even down for the count," wrote Greenland, senior associate dean for clinical and translational research at the Feinberg School of Medicine at Northwestern University in Chicago, in an email to ABC News.
Others, like Dr. Christopher Cannon, say the story might not be over yet. While he admits that the study shows that raising good cholesterol to stave off heart disease is not as straightforward as first imagined, he believes that drugs now being tested that aim to boost HDL levels even higher may hold promise.
"It casts some doubt on the benefits of higher HDL, but the real answers will come from clinical trials of new medications that raise HDL," Cannon, professor of medicine at Harvard Medical School and senior investigator of the TIMI Study Group, said in an email. "We are testing a drug now... that increases HDL by 60 mg/dl on average -- and that will hopefully answer the question on whether HDL is important."
HDL levels are still an important predictor of heart health; for decades, doctors have used this measure as a way of predicting a patient's risk for future heart disease.
"These data do not take away the predictive value of HDL in the general population," said the new study's senior author Dr. Sekar Kathiresan, who is director of preventive cardiology at Massachusetts General Hospital in Boston. "Low amounts of HDL cholesterol have been correlated with an increased risk of heart attack."
Naturally, this correlation made HDL levels seem an attractive target for drugs to reduce the risk of heart disease. To help doctors understand whether this was the case, Kathiresan and his colleagues looked at a group of people who had higher HDL levels because of differences in their genetic makeup. They compared these people with others without this genetic predisposition.
Based on past studies, the researchers expected the patients with higher HDL cholesterol to be protected from a heart attack. To their surprise, that was not the case; there was no difference between the two groups.
So what does this mean for patients? "Just because an intervention raises HDL, we cannot assume that this lowers the risk of a heart attack," Kathiresan said.
This study comes on the heels of several other recent clinical trials that suggest that medications designed to increase HDL are not effective in reducing coronary heart disease. These trials examined, among other things, extended-release niacin and several drugs in an experimental class of medications known as CETP inhibitors.
Several of these studies are still in progress. Yet, none of this research has demonstrated that raising HDL is effective at reducing the rates of heart attacks and heart disease.
Questions Over HDL Therapy Remain
Still, some experts in the field say despite the recent negative studies, many questions remain to be answered. Dr. Michael Miller, director of the Center for Preventive Cardiology at the University of Maryland Medical Center, said the findings of the study belie the complexity of HDL, and that more research is needed before such efforts are abandoned.
"Bottom line: don't throw the baby out with the bathwater," he said in an email. "The inverse relationship between HDL and heart disease is based on a half-century worth of data."
As for what the general public can take away from the research, Dr. Dean Ornish said the findings underscore the idea that when it comes to reducing heart disease risk, it's not a simple matter of good versus bad.
"I think this study shows a fundamental confusion about HDL," said Ornish, founder and president, Preventive Medicine Research Institute in San Francisco. "Not everything that raises HDL is good, and not everything that lowers it is bad."
"Many people, including physicians, get into a simple-minded idea that HDL is 'good cholesterol' and LDL is 'bad cholesterol.' It's not so simple."