HDL Cholesterol

HDL lipoproteins
HDL lipoproteins. MedicalRF.com/Getty Images

HDL cholesterol is the name given to the cholesterol in the bloodstream that is carried by "high density lipoprotein,” or HDL.

HDL cholesterol has been nicknamed "good cholesterol" because reduced levels of HDL cholesterol have been associated with an increased risk of heart attack and stroke, while high HDL levels are associated with a reduced risk.

This nickname, however, implies that we know more about HDL cholesterol than we actually do.

While higher HDL cholesterol levels have been repeatedly associated in clinical trials with improved clinical outcomes, it has not been established that HDL cholesterol actually causes these better outcomes. Furthermore, it has not been established that raising HDL cholesterol levels improves cardiovascular outcomes.

What Does HDL Cholesterol Do?

HDL cholesterol is a complex lipoprotein consisting of cholesterol and several proteins (most predominantly, the apolipoproteins apoA-I apoA-II). The HDL lipoprotein has two main “jobs.”

First, HDL ”scours" the walls of blood vessels and removes excess cholesterol. It carries that cholesterol back to the liver for processing.

Second, HDL has anti-inflammatory effects, and has other properties that tend to keep blood vessels healthy.

So, when we measure HDL cholesterol levels, we are measuring (to a large extent) how much excess cholesterol is being removed from cells and blood vessel walls by the HDL particles for recycling.

The higher the HDL cholesterol levels, it is presumed, the more cholesterol is being removed from where it might otherwise cause damage.

What Are Considered Good HDL Cholesterol Numbers?

In population studies, people with HDL cholesterol levels below 40 mg/DL are at increased risk for coronary artery disease and stroke.

People whose HDL cholesterol levels are above 60 mg/DL have a reduced risk.

How Useful Is It To Increase HDL Cholesterol Levels?

Despite solid evidence of an association between high HDL cholesterol and reduced risk, efforts to prove that increasing HDL cholesterol levels will lower risk, so far, have been unsuccessful.

A meta-analysis that looked at 108 cholesterol treatment trials in 2009 failed to demonstrate that increases in HDL cholesterol improved outcomes. Since then, clinical trials with a new class of drugs that increase HDL cholesterol (the CETP-inhibitors) have been disappointing. And a study aiming to prove the benefits of niacin therapy, which reliably increases HDL cholesterol, also failed.

So at this time we just don’t know how beneficial it is to raise HDL cholesterol levels.

Current Recommendations

Current cholesterol treatment guidelines do not recommend that doctors place their patients on medical therapy for the purpose of increasing HDL cholesterol levels.

However, guidelines do specify that people with low HDL cholesterol levels ought to make the lifestyle changes that are known to reduce cardiovascular risk in general, and which also increase HDL cholesterol levels. These include exercise, weight loss (if overweight), smoking cessation, and adding monounsaturated fatty acids to the diet.

Sources:

Briel M, Ferreira-Gonzalez I, You JJ, et al. Association between change in high density lipoprotein cholesterol and cardiovascular disease morbidity and mortality: systematic review and meta-regression analysis. BMJ 2009; 338:b92.

Stone NJ, Robinson JG, Lichtenstein AH, et al. 2013 ACC/AHA guideline on the treatment of blood cholesterol to reduce atherosclerotic cardiovascular risk in adults: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation 2014; 129:S1.

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