Researchers say an extremely high level of HDL cholesterol can put a person at higher risk of death than someone with normal ‘good’ cholesterol.

Conventional medical wisdom says that high-density lipoprotein (HDL), or “good” cholesterol is linked to better health outcomes than low-density lipoprotein (LDL), also known as “bad” cholesterol.

But Danish researchers have found that high levels of HDL might not be so good after all.

A study, published in European Heart Journal last month, concluded that people with extremely high levels of HDL faced a significantly higher risk of death than people with normal cholesterol levels.

Data from 116,000 people from the Copenhagen City Heart Study, and the Copenhagen General Population Study, were examined over a six-year period.

Few people — 0.4 percent of men and 0.3 percent of women — in the study had HDL levels that were classified as “extremely high.”

But in this small population, the results revealed that extremely high levels of HDL in the bloodstream increased the risk of death by 68 percent in women, and a 106 percent in men.

“These results radically change the way we understand ‘good’ cholesterol,’” said study co-author Børge Nordestgaard, professor at the Department of Clinical Medicine at the University of Copenhagen, in a release.

“Doctors like myself have been used to congratulating patients who had a very high level of HDL in their blood. But we should not longer do so, as this study shows a dramatically higher mortality rate,” he added.

These findings challenge conventional wisdom on so-called “good” cholesterol.

In fact, cholesterol levels are just one of many factors considered when it comes to understanding health outcomes, according to a cardiologist interviewed by Healthline.

The findings from the Copenhagen study would appear to go against prior research.

“There’s been knowledge in the past that certain populations that have higher HDL — much higher HDL — tend to live longer,” Dr. Andrew Freeman, director of cardiovascular prevention and wellness at National Jewish Health and co-chair of the Nutrition and Lifestyle Work Group at the American College of Cardiology in Washington, D.C., told Healthline.

“There was a study on a Sicilian group where there were people that were close to 100 years old, and their HDL was through the roof. So this [Copenhagen study] kind of challenges that.”

While the Sicilian study, and others with similar findings, suggest that high levels of HDL are linked to better health outcomes, it’s difficult to conclusively link cholesterol levels to health outcomes.

Freeman says that some of these findings may be linked to more than just cholesterol levels, pointing out that different studies tend to research different populations.

“Cholesterol in itself doesn’t appear to tell the whole story on cardiovascular risk, but it’s one of the best markers we currently have,” said Freeman. “So there’s definitely more to the cholesterol story that we don’t understand, so I think this raises the question of whether HDL is the be all and end all.”

Medical understanding of HDL’s impact on health outcomes is still a work in progress.

“When I was in medical school, I was basically taught that HDL cleared the bad cholesterol, which is sort of a butchered attempt at an oversimplification,” said Freeman. “But by and large, that is the general understanding. That HDL is a positive thing.”

“But I think we’re also finding that total cholesterol seems to have some effect as well, and the latest calculators that we use look at the total cholesterol as part of their equation. The bottom line is that there are a lot of moving parts here. [The Copenhagen study] is certainly an interesting finding, but there’s a number of caveats. Cholesterol, to me, is not the best surrogate for something that we’re not exactly sure how to measure.”

When it comes to improving one’s own cardiovascular health, Freeman suggests focusing on the basics.

“One of the best ways to get HDL to improve is to eat better and exercise more, and actually to get rid of stress, believe it or not,” he said. “Those are the things that are always discounted. Everyone wants to look to this drug or that pill, but a lot of times the hard work that we put into our own health really pays off the best.”