For decades, doctors have told their patients that high levels of HDL, also known as “good cholesterol,” could protect them from heart disease. However, a new study suggests that a lot of so-called good cholesterol doesn’t mean a lower risk of heart attacks.
That doesn’t mean that HDL levels have no effect.
An analysis of data from nearly 24,000 American adults found that too little HDL cholesterol was associated with an increased risk of heart disease—among white adults but not among black adults, researchers reported Monday in the Journal of the American College of Cardiology.
The new findings surprised researchers, who originally designed their study to understand how cholesterol levels in middle-aged black and white adults without heart disease affected their future risks. Previous research on “good” cholesterol and heart disease included mostly white adults.
“I didn’t expect that high levels of HDL wouldn’t provide protection,” said lead author of the study, Nathalie Pamir, associate professor of cardiovascular medicine at Oregon Health and Science University School of Medicine. “And I certainly didn’t expect that low scores wouldn’t have a predictive value for black adults.”
The new study, which was co-funded by the National Institutes of Health, is part of a growing body of evidence that denies that high HDL cholesterol levels protect against heart disease, experts say, though people may not always get the message.
“Those of us with high HDL have had our doctors patting us on the back,” said Pamir, who also conducts research at OHSU’s Knight Cardicular Institute’s Center for Preventive Cardiology. “We’ve been told your HDL is good, so don’t worry. You’re protected.”
Low-density lipoprotein (LDL) contributes to fat accumulation in arteries, increasing the risk of heart attack and stroke. It has long been believed that high-density lipoprotein (HDL) is protective because it transports cholesterol to the liver, where it is disposed of.
What’s clearer now is that a high HDL level only increases the total cholesterol count.
“At the end of the day, it’s still cholesterol,” Pamir said. “More and more studies are coming out showing that HDL levels above 80 are detrimental to cardiovascular outcomes.”
The results suggest that the algorithms used to calculate a person’s risk of coronary heart disease need to be adjusted, as they are currently at lower risk when HDL levels are high, Pamir said.
Risk calculations also need to consider race, she said, adding that the differences among black adults could be due to socio-economic factors rather than genetics.
What is a healthy cholesterol level?
Currently, a primary focus should be on the total cholesterol count, Pamir said.
Cholesterol levels are measured in milligrams per deciliter of blood (mg/dL). According to the American Heart Association, the optimal total cholesterol level for an adult is around 150 mg/dL, with LDL levels at or below 100 mg/dL.
To study the effects of HDL on the risk of coronary heart disease in more detail, Pamir and her colleagues used data from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study. The researchers focused on 23,901 middle-aged black and white REGARD participants who were enrolled from 2003 to 2007 and had no heart disease at the start.
During an average follow-up period of 10.7 years, there were 1,615 cardiovascular events, 41.1% among black participants and 45.5% among women. High LDL levels and levels of another fat, triglyceride, were associated with an increased risk of coronary heart disease among black and white participants.
Low HDL levels were associated with an increased risk of coronary heart disease among white participants but not among black participants.
Dr. Howard Weintraub, clinical director of the Center for Cardiovascular Disease Prevention at the Leon H. Cheney Division of Cardiology at NYU Langone Health, hopes people are getting the message that high levels of HDL offer no protection.
“Literally every day, someone comes into my office with an HDL of 80 or 90,” said Weintraub, who was not involved in the new study. “When I tell them that, it doesn’t mean they’re bulletproof, they’re dismayed because their doctor told them they shouldn’t worry about their bad cholesterol because the good cholesterol was so good.”
The idea that HDL was protective was so accepted that pharmaceutical companies developed drugs that “raised HDL levels by 100% and people died,” Weintraub said.
Higher HDL levels are usually a sign of a healthy lifestyle, said cardiology specialist Dr. Robert Rosenson.
“People with higher HDL levels are less likely to be overweight, more likely to be active, smoke less often, and are less likely to develop prediabetes,” said Rosenson, director of lipids and metabolism at Mount Sinai Health System in New York, who was not involved in the new study.
Still, Rosenson called the new research important because patients with high HDL levels who should receive cholesterol-lowering drugs may not receive them.
Another significant finding is the difference in cardiovascular risk between black and white patients, said Dr. Leslie Cho, an interventional cardiologist and department head of preventive cardiology and cardiac rehabilitation at Cleveland Clinic.