For decades doctors have been telling their patients that high levels of HDL, otherwise known as "good cholesterol," could protect them from heart disease. But a new study suggests that having a lot of so-called good cholesterol doesn't mean a lower risk of heart attacks.
That doesn't mean HDL levels have no impact.
An analysis of data from nearly 24,000 American adults revealed that too little HDL cholesterol was associated with an increased risk of heart disease - in white adults, but not in Black adults, researchers reported Monday in the Journal of the American College of Cardiology.
The new findings surprised the researchers, who originally designed their study to understand how cholesterol levels in Black and white middle-aged adults without heart disease affected their future risks. Previous research on "good" cholesterol and heart disease consisted of mostly white adults.
"I did not expect high levels of HDL would not be protective," said the study's senior author, Nathalie Pamir, an associate professor of cardiovascular medicine in the Oregon Health and Science University School of Medicine. "And I certainly did not expect low levels to have no predictive value for Black adults."
The new research, co-funded by the National Institutes of Health, is part of a growing body of evidence disputing that high HDL cholesterol levels are protective against heart disease, experts say, although people may not always be getting the message.
"Those of us with high HDL have been getting a pat on the back from our doctors," said Pamir, who is also a researcher at the Center for Preventive Cardiology at OHSU's Knight Cardiovascular Institute. "We've been told your HDL is good so don't worry. You're protected."
Low density lipoprotein, or LDL, contributes to fatty buildups in the arteries, raising the risk of heart attack and stroke. It had long been thought that high density lipoprotein, or HDL, is protective because it carries cholesterol to the liver, where it is disposed of.
What's clearer now is that high HDL just adds to the total cholesterol number.
"It's still cholesterol at the end of the day," Pamir said. "More and more studies are coming out showing that HDL levels above 80 are detrimental with regards to cardiovascular outcomes."
The findings suggest that the algorithms used to calculate an individual's coronary heart disease risk need to be adjusted since they currently show a lower risk if HDL is high, Pamir said.
Risk calculations also need to take race into account, she said, adding that the differences seen in Black adults may be because of socioeconomic factors rather than genetics.
What is a healthy cholesterol level?
Right now, a major focus should be on the total cholesterol number, 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 about 150 mg/dL, with LDL levels at or below 100 mg/dL.
To take a closer look at the impact of HDL on coronary heart disease risk, Pamir and her colleagues turned to data from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study. The researchers focused on 23,901 middle-aged Black and white REGARDS participants who were enrolled from 2003 to 2007 and who had no heart disease at the outset.
During a mean 10.7 years of follow-up, there were 1,615 cardiovascular events, 41.1% in Black participants and 45.5% in women. High LDL and the level of another fat known as triglyceride were associated with an increased risk of coronary heart disease in Black and white participants.
Low HDL levels were associated with an increased risk of coronary heart disease in white participants, but not Black participants.
Dr. Howard Weintraub, clinical director of the Center for the Prevention of Cardiovascular Disease at the Leon H. Cheney Division of Cardiology at NYU Langone Health, hopes people get the message that high HDL levels aren't protective.
"Literally, on a daily basis someone comes to my office with an HDL of 80 or 90," said Weintraub, who was not involved in the new research. "When I tell them that doesn't mean they are bulletproof, they are crestfallen because their doctor told them not to 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 typically a marker 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, less likely to be smokers and less likely to have prediabetes," said Rosenson, director of lipids and metabolism at the Mount Sinai Health System in New York, who was not involved with the new study.
Still, Rosenson called the new research important because patients with high HDL levels who should be getting cholesterol-lowering drugs may not be getting them.
Another significant finding is the difference in cardiovascular risk between Black and white patients, said Dr. Leslie Cho, an interventional cardiologist and section head of preventive cardiology and cardiac rehabilitation at the Cleveland Clinic.
"Underrepresented minority groups should demand more clinical (trial) representation," said Cho, who was not involved in the new research. "It's really important."
This article was originally published on NBCNews.com