Cholesterol

AHA Scientific Position

Cholesterol is a soft, waxy substance found among the lipids (fats) in the bloodstream and in all your body's cells. It's an important part of a healthy body because it's used to form cell membranes, some hormones and other needed tissues. But a high level of cholesterol in the blood--hypercholesterolemia--is a major risk factor for heart attack (coronary heart disease).

Cholesterol and other fats can't dissolve in the blood. They have to be transported to and from the cells by special carriers of lipids and proteins called lipoproteins. There are several kinds, but the ones to be most concerned about are low density lipoprotein (LDL) and high density lipoprotein (HDL).

LDL Cholesterol

Low density lipoprotein is the major cholesterol carrier in the blood. When a person has too much LDL cholesterol circulating in the blood, it can slowly build up within the walls of the arteries feeding the heart and brain. Together with other substances, it can form plaque--a thick, hard deposit that can clog those arteries. This condition is known as Atherosclerosis. The formation of a clot (or thrombus) in the region of this plaque can block the flow of blood to part of the heart muscle and cause a heart attack. If a clot blocks the flow of blood to part of the brain, the result is a stroke. A high level of LDL cholesterol reflects an increased risk of heart disease. That is why LDL cholesterol is often called "bad" cholesterol.

HDL Cholesterol

About one-third to one-fourth of blood cholesterol is carried by high density lipoprotein or HDL. Medical experts think HDL tends to carry cholesterol away from the arteries and back to the liver, where it's passed from the body. Some experts believe HDL removes excess cholesterol from atherosclerotic plaques and thus slows their growth. HDL is known as "good" cholesterol because a high level of HDL seems to protect against heart attack. The opposite is also true: a low HDL level indicates a greater risk.

See American Heart Association for more information on Cholesterol.