Harvard Heart Letter

The lesser-known fat in your blood

Emerging evidence suggests that high triglycerides play a bigger role in heart disease than previously thought.

When you have a test to measure the fats in your blood (known as a lipid panel), the two numbers that get the most attention are the levels of your low-density lipoprotein (LDL), or "bad" cholesterol, and high-density lipoprotein (HDL), or "good" cholesterol. High levels of LDL (as well as low levels of HDL) track closely with the artery-clogging process at the root of most cases of coronary artery disease. But triglycerides—the most common type of fat both in food and in the bloodstream—are often an afterthought, mostly because their relevance to cardiovascular disease has been uncertain.

Now, growing evidence suggests that triglycerides may be more important than HDL, says Dr. Sekar Kathiresan, director of preventive cardiology at Harvard-affiliated Massachusetts General Hospital. "Most people with low HDL levels have high triglycerides—they're two sides of the same coin. It now looks like low HDL may just be a marker for heart disease risk. The true causal factor for atherosclerosis in this pair may be triglycerides," he says.

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