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Why Some Good HDL Cholesterol May Harm Your Heart

Why some good cholesterol may harm your heart

Many people recognize high-density lipoprotein (HDL) cholesterol as the “good” cholesterol, but a new study suggests not all HDL cholesterol may be beneficial. In fact, some good cholesterol may harm your heart.

When is good cholesterol bad?

Researchers at Harvard School of Public Health (HSPH) discovered that a small protein called apolipoprotein C-III (apoC-III) may increase the risk of heart disease when it is found on the surface of HDL cholesterol. HDL cholesterol without apoC-III, however, may protect the heart.

The presence or absence of apoC-III could be a reason why some studies of heart disease that involve raising HDL cholesterol have not consistently yielded positive results. In fact, this discovery, noted Frank Sacks, professor of cardiovascular disease prevention at HSPH and the study’s senior author, because “it could lead to better evaluation of risk of heart disease in individuals and to more precise targeting of treatments to raise the protective HDL or lower the unfavorable HLD with apoC-III.”

What is apoC-III?
Apolipoprotein C-III is a small protein with pro-inflammatory properties that can be found on various types of lipoproteins:

  • Low-density lipoprotein (LDL) cholesterol, which is typically viewed as “bad” cholesterol
  • Very-low-density lipoproteins, which contain the highest amount of triglyceride. High VLDL levels place individuals at increased risk of coronary artery disease
  • Chylomicrons, which consist primarily of triglycerides and only a tiny amount of cholesterol, carry triglycerides and cholesterol from the small intestine to other tissues
  • HDL cholesterol, which, at high levels, has traditionally been associated with a low risk of coronary heart disease

Increased levels of apoC-III have been associated with elevated triglycerides, which are a type of lipid present in the blood that have a role in atherosclerosis and in heart disease and are also involved in insulin resistance, which can lead to type 2 diabetes.

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In the new study, investigators examined blood samples from 32,826 women who had participated in the Nurses’ Health Study and from 18,225 men in the Health Professionals Follow-up Study. A total of 634 coronary heart disease cases were reported during the 10 to 14 years of follow-up, and they were matched with controls.

Researchers conducted an evaluation of the blood samples and, after allowing for various factors, including lifestyle cardiovascular risk factors, they found that HDL cholesterol without apoC-III was associated with heart-protective properties while HDL cholesterol with apoC-III presented a higher risk of coronary heart disease.

Only 13% of HDL cholesterol had the apoC-III. However, men and women who had HDL apoC-III in the highest 20% of the population had a 60% greater risk of experiencing coronary heart disease.

The study’s findings indicate that good cholesterol does not always live up to its nickname. They also suggest that measuring both subtypes of good cholesterol could help clinicians better determine an individual’s risk of heart disease.

Bobik A. Apolipoprotein CIII and atherosclerosis. Circulation 2008; 118:702-4
Harvard School of Public Health

Image: Wikimedia Commons