The truth about HDL and its role in protecting people from heart disease
In the fight against heart disease, HDL has been cast as the “superhero,” swooping in to save the day and protect the heart against its evil nemesis, LDL.
But a new study paints HDL as more of a Clark Kent than a Superman. This study, published in May by The Lancet, found that genetically high levels of HDL (high density lipoprotein) offered no extra protection against heart disease. In fact, it concluded there was no difference in heart attack risk between people with genetically higher levels of HDL and those with somewhat lower levels of HDL.
The study, which analyzed the genes of thousands of people for variations in HDL and LDL (low density lipoprotein), has sparked discussion in the medical community.
What is HDL’s role in protecting people from heart disease? Does it even matter?
Most definitely, says cardiologist K. Lance Gould, MD, a professor of internal medicine at The University of Texas Health Science Center at Houston (UTHealth) Medical School and director of the Weatherhead PET Center for Preventing and Reversing Atherosclerosis. He says some patients with genetically high levels of HDL still develop heart disease, as was found in the study. The converse is also shown possible, as patients with genetically low HDL levels may never develop heart disease.
“I have 20 patients right now who primarily have genetically high levels of HDL, and they all have cardiac disease,” Gould says. “In most people, however, the higher the level (of HDL), the better.”
Gould aims to double HDL levels in his patients with high cholesterol—for example, from 25 milligrams per deciliter to 45 milligrams per deciliter. The American Heart Association considers HDL levels of 45 to 60 milligrams per deciliter protective against heart disease, while HDL of less than 40 milligrams per deciliter is considered low. Patients, he adds, should also focus on lowering their LDL to receive the maximum benefit from raising their HDL.
HDL is just one of the many factors that reduce the risk for heart disease, Gould says. In fact, the body makes different types of HDL and not all of them are good for you.
“It gets complicated,” he admits.
The good, the bad…and the inside of your arteries
Going back to the superhero scenario, there are three main “characters,” or components of cholesterol: LDL, HDL and Lp(a). Concentrating on the first two, LDL is considered the “villain” (“To remember it, think of LDL as ‘low down,’” Gould says).
LDL circulates in the blood until it builds up inside the walls of the arteries, forming a thick, hard deposit called plaque. Too much plaque buildup narrows the arteries and makes them less flexible, a condition known as atherosclerosis. A heart attack or stroke can occur if plaque cracks open, which causes a blood clot to block the narrowed artery.
LDL is at its worst when it is small—easily stacking up to form plaque inside the artery. It is not as threatening in its larger and fluffy state. Increasing HDL levels and decreasing triglycerides (fat that accumulates in the blood) helps convert small LDL to larger, fluffier LDL.
Experts believe that HDL, or the “hero,” protects the heart by removing LDL from the arteries and reducing inflammation, which helps facilitate blood flow. But some people have another, smaller type of HDL—HDL’s “evil twin”—that harms the heart, rather than helps.
“If it is the wrong type of HDL, it clearly can cause heart disease,” Gould says. He adds that people often make the mistake of equating the amount of HDL in the blood with how much protection it offers against heart disease. Instead, we should pay attention to how often HDL removes LDL cholesterol from the artery walls and carries it to the liver, where it is eliminated from the body, during a process called HDL turnover.
“It is the turnover that’s important since it’s what protects the heart,” he says.
Look at the big picture
While The Lancet study raises some interesting questions, the public should not discount the role of HDL in preventing heart disease, or abandon medication that helps increase HDL, according to Gould. He says a body of established evidence shows raising HDL through changes in lifestyle and medication helps lower the risk of heart disease.
Similarly, men and women looking to lower their cholesterol should focus on the big picture instead of one component of cholesterol. Treating heart disease is complex, Gould says. Genetic factors, medications (including statins to lower cholesterol and niacin to raise HDL) and lifestyle factors all play a role and must be tweaked to find the right combination that works for each individual patient. Developing a treatment program that takes all variables into account is crucial.
“The basic fact is, people with low rates of HDL die of vascular disease more than anyone else,” Gould says. “Lifestyle factors that raise HDL, such as weight control and exercise, also reduce diabetes, blood pressure and LDL cholesterol, and have a profound benefit on cardiovascular health.”