For half a century cholesterol has been divided into good and bad categories. Low-density lipoprotein (LDL) is considered the "bad" cholesterol as it's responsible for blocking arteries and causing stroke or heart attacks, while high-density lipoprotein (HDL) has been seen as the "good" form of cholesterol as it catches LDL in the bloodstream and takes it back to the liver.
Back in the 1970s a foundational research project, called the Framingham Heart Study, detected a consistent link between increased HDL levels and decreased heart attack risk. The association has informed clinical practice for the decades since it was found, with doctors frequently suggesting higher HDL levels can be protective against heart attack.
Since the Framingham study, researchers have conducted several follow-up investigations that have delivered pretty inconsistent results. When looking at White European ethnicities, low HDL levels can certainly be linked to increased heart disease risk, but when more racially diverse cohorts were assembled that association tended to disappear.
Nathalie Pamir, from the Oregon Health & Science University and senior author on the new study, said it is important to understand the racial differences that could be at play when analyzing the effect of HDL levels on heart attack risk. Pamir's research looked at data from a long-term stroke study tracking more than 20,000 people for over a decade.
“The goal was to understand this long-established link that labels HDL as the beneficial cholesterol, and if that’s true for all ethnicities,” said Pamir. “It’s been well accepted that low HDL cholesterol levels are detrimental, regardless of race. Our research tested those assumptions.”
The data Pamir and colleagues analyzed were from a project called REGARDS (the Reasons for Geographic and Racial Differences in Stroke), a study designed to investigate the different risk factors for stroke between White and Black middle-aged adults in the United States. The initial findings confirmed a general presumption, high levels of "bad" LDL cholesterol do increase a person's risk for cardiovascular disease, regardless of ethnicity. But the rest of the investigation turned up some surprises.
Looking at so-called "good" HDL cholesterol, the research found low levels only correlated with increased heart disease in White adults. And perhaps most striking, high HDL levels were not associated with less heart attacks in either White or Black study participants.
“What I hope this type of research establishes is the need to revisit the risk-predicting algorithm for cardiovascular disease,” added Pamir. “It could mean that in the future we don’t get a pat on the back by our doctors for having higher HDL cholesterol levels.”
It's currently unclear why HDL cholesterol would have a different impact on heart disease risk between ethnicities. Sean Coady, an epidemiologist from the National Heart, Lung, and Blood Institute said these findings call for more study into the properties of HDL cholesterol.
“HDL cholesterol has long been an enigmatic risk factor for cardiovascular disease,” said Sean Coady, who didn't work on this new study. “The findings suggest that a deeper dive into the epidemiology of lipid metabolism is warranted, especially in terms of how race may modify or mediate these relationships.”
The study was published in the Journal of the American College of Cardiology.
Source: NIH
