The HDL story gets murky

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Those who have had their cholesterol levels tested are typically informed that there are two types of primary importance: LDL, or bad cholesterol, and HDL, which is the good kind. And while much research has determined that reducing LDL protects against heart disease and cardiovascular events, some doctors have wondered whether raising HDL actually achieves the same effects. However, earlier classes of drugs (Pfizer s Torcetrapib, most notably) designed to increase HDL failed to demonstrate any beneficial effect, and were thus abandoned.

Now a new analysis, published in The Lancet, offers another perspective on the HDL question by providing further evidence that merely having an elevated HDL does not necessarily result in a reduced risk of heart attack. Researchers from Massachusetts General Hospital, the Broad Institute, and Harvard Medical School compared the incidence of heart attack between two groups of people: The first cohort was comprised of those with a genetic variation that resulted in naturally high HDL levels, while the second group the control group had no such genetic predisposition to high HDL. After analyzing over 20,000 heart attack cases from 20 studies, the researchers found that people with a genetic tendency toward higher HDL concentrations did not have a lower risk of heart attack.

Interventions (lifestyle or pharmacological) that raise plasma HDL cholesterol cannot be assumed ipso facto to lead to a corresponding benefit with respect to risk of myocardial infarction (heart attack), the authors concluded.

But not so fast, says ACSH s Dr. Gilbert Ross. An elevated HDL due to a genetic predisposition is not the same thing as HDL concentrations that have increased by means of lifestyle changes, or even due to some drug interventions, he says. You cannot extrapolate data from people who have these very specific genetic variations and than widely apply them to the general population to conclude that HDL is not a protective factor in lowering heart disease. That being said, however, we also have no evidence to show that an elevated HDL is directly responsible for protecting the heart rather than being merely an association or biomarker.

To say that you shouldn t worry about HDL would be overly simplistic, adds ACSH s Dr. Elizabeth Whelan. For instance, we do know that exercise, abstaining from smoking, and moderate alcohol consumption are all associated with a decreased risk of heart disease, as well as with increased HDL levels. Thus, it s difficult to separate the role of the lifestyle changes from the effects of HDL, if there are any.