(CBS News) -- We've heard it all before: There's "good" cholesterol, called high-density lipoprotein (HDL), that provides protective benefits against heart attacks and then there's "bad" LDL cholesterol, which raises risk for heart problems in high levels.
A new study finds that HDL cholesterol might not boost your heart health as doctors once thought.
The study looked at the genes of about 170,000 individuals, looking for variations in DNA that earlier research shows naturally raise HDL levels in those who possess them. After looking for these 15 genetic variations - called single nucleotide polymorphisms (SNPs) - in the participants, the researchers discovered none of these variations actually reduced their risks for having a heart attack, compared with people who didn't have the variations.
For example, carriers of one such SNP, so-called "protein-coding change in the endothelial lipase gene," have HDL levels that are naturally 10 percent higher than most people, an elevation that's expected to reduce heart attack risk by 13 percent. But the study found they in fact had the same risk as non-carriers.
"It's been assumed that if a patient, or group of patients, did something to cause their HDL levels to go up, then you can safely assume that their risk of heart attack will go down," senior author Dr. Sekar Kathiresan, director of preventive cardiology at Massachusetts General Hospital, and associate professor of medicine at Harvard Medical School, said in a news release. "This work fundamentally questions that."
Kathiresan told WebMD that HDL remains an important tool for assessing heart disease risk, but the new research raises questions about the benefits of taking medication to raise HDL levels.
Cholesterol in the blood is carried by particles called lipoproteins, which come in different sizes and densities, according to the researchers. There is a well-established connection between elevated LDL levels and heart attack, and decades of research - including genetic studies similar to the new study - paved the way for the development of lipid-lowering drugs known as statins.
But research has been less clear on HDL, since a study more than 30 years ago found the higher levels of HDL a person had, the least likely they were to have a heart attack. Mouse studies since then have reported similar findings, but researchers haven't been able to prove the link conclusively. The new study may provide the clearest evidence yet of the role HDL plays, the researchers said.
"Through our research, we have found that all roads that raise HDL do not always lead to the promise land of reduced risk of heart attack," said study co-author Dr. Benjamin F. Voight, an assistant professor of pharmacology at the University of Pennsylvania, said in a university written statement.
Experts commenting on the study appeared to agree with that sentiment.
"The current study tells us that when it comes to HDL we should seriously consider going back to the drawing board, in this case meaning back to the laboratory," Dr. Michael Lauer, director of the division of cardiovascular sciences at the National Heart, Lung and Blood Institute, told The New York Times. "We need to encourage basic laboratory scientists to figure out where HDL fits in the puzzle - just what exactly is it a marker for."
American Heart Association past president Dr. Robert Eckel, a professor of medicine at the University of Colorado School of Medicine in Aurora, told WebMD the new research casts more doubt on the strategy of raising HDL to lower heart and stroke risk.
"HDL levels are related to risk, but that doesn't mean that raising HDL is beneficial," he says. "What we do know is that lowering LDL has a big impact on risk, so the take-home message remains, 'Get those LDL numbers down.'"
Ryan Jaslow, CBS NEWS