HDL (high-density lipoprotein cholesterol) has been touted for years as the "good" cholesterol and that high levels — the higher the better — would protect you from cardiovascular disease.
That's not necessarily true, says a new study from the University of Maryland School of Medicine which examined nearly 25 years of data from the Framingham Heart Study's Offspring Cohort.
Researchers found that HDL levels alone don't do the trick. Its ability to protect the heart depends on the levels of two other blood fats or lipids — LDL or low-density lipoprotein cholesterol and triglycerides (TG). If those two lipids aren't within normal ranges, even a high HDL may not be protective.
The study followed 3,590 men and women between 1987 and 2011. They had no known cardiovascular disease at the beginning of the study, but participants included those with both high and low HDL levels, and both normal and high levels of LDL and triglycerides.
“Nobody has really looked at an isolated low and isolated high HDL, and whether or not other factors, such as triglycerides and LDL, make a difference in the risk of cardiovascular disease,” says senior author Michael Miller, M.D.
The study found that HDL alone did not correctly predict cardiovascular risk, and that LDL and triglyceride levels modified risk in participants with both low and high levels of HDL.
As might have been predicted, patients who had low HDL levels combined with high levels of LDL or triglycerides or both, had a higher risk of cardiovascular disease of 30 to 60 percent. But in patients with high levels of HDL, cardiovascular risk was not reduced if LDL and triglycerides were above 100 mg/dL.
According to the National Institutes of Health, HDL levels of 60 mg/dL and higher are believed to be protective against heart disease, while levels below 40 mg/dL are considered a major risk factor for cardiovascular disease. LDL levels of 100 mg/dL or less are ideal, and levels 160 mg/dL and above are high. Triglycerides levels of lower than 150 mg/dL are considered ideal, while 200 mg/dL and above are high.
“There’s no question that HDL does have a protective role, as we also confirm in the study, but HDL has been hyped-up,” says Miller. “HDL really should be viewed as a third priority, with LDL on top and TG second.”
The study was published in Circulation: Cardiovascular Quality and Outcomes.
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