Even though low-density lipoprotein (LDL) cholesterol can increase the risk of heart attacks and strokes, a new survey suggests that most people who survive these events have no idea that LDL is “bad cholesterol.”

LDL cholesterol plays a key role in the buildup of fatty deposits inside arteries that can cause these blood vessels to narrow over time, increasing the risk of heart attacks and strokes. And three out of four heart attack and stroke survivors have high cholesterol, according to the survey from the American Heart Association (AHA).

Despite this, fewer than half of heart attack and stroke survivors prioritize lowering their cholesterol, or even know their own LDL levels, the survey found.

Donald Lloyd-Jones, MD, a past president of the AHA and the chair of preventive medicine at the Northwestern University Feinberg School of Medicine in Chicago, has answers to some of the most common questions about LDL cholesterol.

Everyday Health: How exactly does LDL cause heart attacks and strokes?

Donald Lloyd-Jones: The low-density lipoprotein (LDL) particles containing cholesterol can accumulate in the walls of our arteries over time when people have risk factors like high blood pressure, smoking, or diabetes. It can also accumulate over time as we age, even in people without high blood pressure.

The accumulation of these particles leads to plaque formation. When plaques grow and become inflamed, they can rupture, causing a blood clot to form in the artery that blocks blood flow to the heart in a heart attack, or to the brain in certain types of stroke. In some cases, plaques alone can grow to the point where they restrict blood flow enough to cause a heart attack, when the heart is under stress for other reasons and demand outstrips blood supply.

EH: Why is it important to know your LDL and cholesterol numbers?

DL-J: LDL cholesterol is a silent risk factor. Without measuring it through a blood test it is impossible to know what your levels are. There is no “normal” level, so it is important to discuss with your doctor whether your level is optimal, or too high, for your situation.

EH: How often do I need to get my cholesterol checked?

DL-J: If you are healthy and without a history of heart disease and stroke, the AHA recommends having your cholesterol checked about every five years. If you have risk factors like diabetes, or a history of very high cholesterol, it should be as often as annually. The cholesterol numbers can be used to calculate your risk for heart attack or stroke, which can help you and your doctor decide if your levels are too high for you. If you have had a heart attack or stroke you should have your levels checked at least once a year, and more often if you are starting medication or adjusting doses of medication.

EH: What’s a good LDL number?

DL-J: If someone is healthy and without risk factors for heart attacks and strokes, like smoking or having diabetes, they should shoot for LDL levels below 100 milligrams per deciliter (mg/dL). But if they have risk factors, and especially if they have heart disease or have had a stroke, they need to get LDL levels down to 70 mg/dL or even lower in some cases.

Lower is always better, but how aggressively we treat LDL depends on the circumstances. Healthy people without risk factors would most likely work on lifestyle changes to manage LDL, but people with risk factors would most likely need medication to lower their cholesterol in addition to this.

EH: What can I do to lower LDL?

DL-J: Dietary changes can be important for many people to help control LDL cholesterol. In particular, people should avoid red meats, dairy fats, and egg yolks, as well as tropical oils like coconut oil and cod liver oil. They can focus on healthier fats and cook with things like olive or canola oil. There are health benefits to this even if people don’t have high cholesterol.

When people do have high cholesterol, they will often need to take statins or other cholesterol-lowering medications, however. Especially when people have already had a heart attack or stroke, or when they have other risk factors, they need a more aggressive treatment plan that includes medication and may include a lower target level for LDL than you need for somebody who is healthy and has no risk factors.

EH: Are there things people do that raise LDL cholesterol?

DL-J: LDL cholesterol levels in the blood are determined in part by our mix of genes that we inherit from our parents. And some people are sensitive to the amount of cholesterol and saturated fat in their diet, which means when they eat high-fat dairy products like butter or cheese or eat a lot of red meat, it can cause their LDL cholesterol to increase. This is only about 25 to 30 percent of the population that’s sensitive to these foods, for whom diet can make a major impact on their cholesterol levels. For everybody else, diet doesn’t make a big difference in their numbers. And how much you exercise doesn’t impact your LDL cholesterol.