When his patients want to talk about cholesterol, cardiologist Dariush Mozaffarian knows he has his work cut out for him. Confusion about the much-maligned substance is common: Surveys of adults around the world show that although most people are concerned about their cholesterol, fewer than half know recommended cholesterol levels or understand what those numbers mean for their health.

“There’s a lot of confusion and controversy around cholesterol,” says Mozaffarian, an associate professor of medicine and epidemiology at Harvard Medical School. “There is even confusion among the scientists who study it.” That confusion can lead both patients and doctors astray, which is why Mozaffarian and many other physicians are working to dispel cholesterol myths.

“People talk and write about cholesterol as ‘artery-clogging fat,’ ” Mozaffarian says. “But this idea that you eat something, it gets into your bloodstream and it clogs your arteries is just false. Nothing remotely like that is happening.”

In fact, most of the cholesterol in your body doesn’t come from food — it’s made by the body itself. The liver produces this waxy, fatlike substance, which is just one component — along with calcium and other debris — of the plaque that can clog arteries and cause heart attacks and certain kinds of stroke. But most of the time, cholesterol isn’t there to cause trouble; it travels through the bloodstream doing a number of important jobs. It helps make key hormones such as estrogen and testosterone, synthesize vitamin D, and build and maintain cell membranes, all of which are “absolutely mandatory” for good health, says Michael Blaha, director of clinical research at the Johns Hopkins Ciccarone Center for the Prevention of Heart Disease.

To transport and store cholesterol, the liver packages it into lipoproteins — particles that are part fat and part protein. Low-density lipoproteins (LDL) carry cholesterol to the body’s cells; high-density lipoproteins (HDL) bring it back to the liver, where it gets recycled or excreted. Cholesterol tests, or “lipid panels,” measure the levels of lipoproteins circulating in the blood, along with triglycerides, fats that are often packaged with lipoproteins.

In a healthy cardiovascular system, LDL, HDL and triglycerides are in balance. Smoking, lack of exercise, obesity, poor diet and other factors can throw the balance out of whack, and that’s what sets the stage for plaque buildup and heart disease, Mozaffarian says.

Until recently, physicians focused on the total cholesterol level — the combination of LDL and HDL in the blood — when screening patients for heart disease risk, and they had good reason, says Paul Ridker, director of the Center for Cardiovascular Disease Prevention at Brigham and Women’s Hospital in Boston.

“Studies showed us that high cholesterol levels were one of the most important risk factors for the development of heart attack and stroke, and we had evidence that lowering cholesterol lowers the risk of heart attack and stroke,” Ridker says. “You can’t say that about most everything else.”