It began as a medical mystery. In the 1920s, cardiovascular disease became the number-one cause of death in the United States. No one understood why. In 1948, the U.S. Public Health Service commissioned the Framingham Heart Study, an ambitious 50-year study involving thousands of people living in Framingham, Massachusetts. A breakthrough discovery happened 13 years into the study, in 1961: Scientists found that an overabundance of cholesterol—a soft, waxy substance that the body produces, which also occurs naturally in many foods—could lead to clogged arteries and, eventually, severe cardiovascular problems.

The results of the Framingham Heart Study led to far-reaching efforts to drop cholesterol levels through diet, exercise, and medication—and they worked. Accord-ing to the Centers for Disease Control and Prevention, the percentage of American adults with hazardously high cholesterol levels dropped from 33 percent in the early 1960s to just 16 percent in the early 2000s. In that same time period, the average adult cholesterol level dropped from 222 mg/dL to 200 mg/dL. Even so, heart disease remains the number-one killer among men and women in the United States, and researchers continue to refine their understanding of why.

Cholesterol isn’t all bad. In fact, the body uses it to waterproof cells, repair wounds, build hormones, and fuel brain function. It’s when low-density lipoprotein (LDL, often called “bad” cholesterol) levels become too high and high-density lipoprotein (HDL, or “good” cholesterol) levels become too low that problems arise.

LDL molecules range in size and density; those that are smaller can penetrate blood vessels and cause vessel damage, explains Jessica Tran, ND, of the Southwest Naturopathic Medical Center in Scottsdale, Arizona. As the body repairs damage from these molecules, plaque builds up, causing decreased blood flow and artery blockages.

One fact on which scientists agree: Maintaining cardiovascular health isn’t as simple as avoiding saturated fats and cholesterol-rich foods—or popping cholesterol-lowering pills. And while it’s still a good idea to keep cholesterol levels in check, other details are equally, if not more, important. Here are a few of the most common myths and truths about your cholesterol.