Scientists have linked high-density lipoproteins (HDL), also known as "good" cholesterol, to lower cardiovascular risk for quite some time, but the Journal of the American Medical Association released a study on June 3, 2008, saying that HDL might not be protective after all.
The study looked at 57,000 Danish patients between 1976 and 2007 and found no protective effect on heart disease. Included in the patient population were 148 individuals with Tangier disease, a rare genetic condition. Of relevance, individuals with Tangier disease have very low HDL levels, so researchers expected that their chance of having heart disease would be double those without the disease, but the study found that they were not at increased risk, even after adjusting for age and heart disease risk factors.
To date, drug makers have spent over $1 billion based on the belief that HDL helps unclog arteries. Previous studies included individuals with both high triglycerides and low HDL, but the triglycerides might have caused the increased risk. Thus far, the majority of data on HDL relies on animal studies and it is not clear that results will translate to humans, according to lead study author Tybjaerg-Hansen.
Pfizer spent big bucks on its now-infamous drug torcetrapib, which it did show to raise HDL levels, but did not prove cardiovascular benefits. In fact, it increased deaths, leading to Pfizer discontinuing research in early 2007. Other major developers of drugs to increase HDL include Merck and Roche. While Pfizer's torcetrapib program has been halted, Merck will not be stopping research, since the company believes there remains significant evidence that increasing HDL provides cardiovascular benefits. Roche plans to take its drug to FDA for approval sometime after 2011.