Does HDL reduce the risk of heart attacks? - New study asks questions.

A new study has raised questions among researchers regarding a theory that has entered the common wisdom – that “good cholesterol” reduces the risk of heart attacks. Pharmaceutical companies have spent more than a billion dollars pursuing this theory, to limited results.

The study found that among people with a genetic condition that severely limits their levels of HDL (or “good”) cholesterol were no more likely to suffer from a heart attack than those with normal amounts of the HDL cholesterol.

The study was published in the Journal of the American Medical Association. Prior studies found that HDL cholesterol ferried dangerous plaque out of the body, which lead many to believe that patients with low HDL cholesterol levels would have a much higher risk of heart attack.

The major pharmaceutical companies have sent years of time and hundreds of millions of dollars after drugs that increase HDL cholesterol production. This new study may show that all their efforts were wasted. Anne Tybjaerg-Hansen, one of the authors of the study and a clinical biochemistry researcher at Copenhagen University Hospital, told Bloomberg, “There is really no evidence that this method is going to work. `This theory has been around for a long time, but this study just doesn't support it.''
The misconception may have originated when researchers chose their subjects for HDL cholesterol studies. Most of the patients had high levels of triglycerides. The high levels of triglycerides may have caused the increased risk of heart attack, not their low HDL cholesterol levels.

Even so, Yale Mitchel, vice president of cardiovascular disease research for Merck, says the study won’t stop his work in HDL-raising drugs.

"The hypothesis on whether CETP inhibition is a benefit or not hasn't been tested and it is too attractive a mechanism to disregard right now," said Mitchel. "We have to be careful about not over interpreting it at this point. There is a large contextual database that suggests low HDL levels are associated with an increased risk.''

A further study released in 2009 found something similar. Although there is an inverse correlation between HDL levels in the blood and risk for heart disease, there is no proof that medical intervantion to lower HDL do much good. "After adjustment for changes in LDL, the change in HDL was not associated with a reduction in the risk for CHD events."