Cholesterol is one of the most familiar medical words today. Everyone knows "something" about it, but mostly cholesterol is associated in our mind with something "bad" and "unwanted" that happens to old and overweight people. The facts show that about 20 percent of the U.S. population has high blood cholesterol levels.

Actually cholesterol is a waxy, fatlike substance (lipid) that your body needs for many important functions, such as producing new cells , some hormones, vitamin D, and the bile acids that help to digest fat. It is present in cell walls or membranes everywhere in the body, including the brain, nerves, muscle, skin, liver, intestines, and heart.

In fact our bodies need cholesterol to function normally, but too much cholesterol can be bad for our health. Why? Cholesterol and other fats can't dissolve in the blood. They have to be transported to and from the cells by special carriers. Cholesterol travels through your blood attached to a protein. This cholesterol-protein package is called a lipoprotein. Lipoproteins are high density or low density depending on how much protein there is in relation to fat.

Low-density lipoprotein (LDL) is the major cholesterol carrier in the blood. If too much LDL cholesterol circulates in the blood, it can slowly build up in 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. When the coronary arteries become narrowed or clogged by cholesterol and fat deposits (a process called atherosclerosis) and cannot supply enough blood to the heart, the result is coronary heart disease. If the blood supply to a portion of the heart is completely cut off by total blockage of a coronary artery, the result is a heart attack. This is usually due to a sudden closure from a blood clot forming on top of a previous narrowing. Low-density lipoprotein cholesterol is called "bad" cholesterol because it can cause cholesterol buildup and blockage of your arteries. LDL is mostly fat with only a small amount of protein.

About one-third to one-fourth of blood cholesterol is carried by high-density lipoprotein (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 plaques and thus slows their growth. HDL is called "good" cholesterol because it helps prevent cholesterol from building up in your arteries. It is mostly protein with only a small amount of fat.