Cholesterol is a fatty substance that is essential for proper body functioning. But elevated blood levels of cholesterol increase the risk of coronary heart disease and heart attacks.
The government's National Cholesterol Education Program has estimated that at least 36 million people—about two thirds of them age 45 or older—have blood cholesterol levels high enough to merit treatment with cholesterol-lowering drugs. Yet only 12 to 15 million of them are currently taking such medication, and many (probably most) are taking too small a dose. The landmark Heart Protection Study, published in the Lancet in 2002, concluded that cholesterol-lowering drugs called statins can produce substantial benefits in a much wider range of high-risk people than had been previously thought—including people over age 70, women, and anyone with vascular disease or diabetes, regardless of whether they have high cholesterol levels.
Cholesterol is a white, waxy lipid (fat) that is present in the tissues of humans and other animals and, thus, in all foods from animal sources. Although cholesterol is essential for many bodily functions, it isn't an essential nutrient, meaning that the diet does not need to contain cholesterol to meet the body's requirements. The liver manufactures all the cholesterol that the body needs. Particles called lipoproteins, formed in the liver, transport cholesterol and other fats through the bloodstream. The three lipoproteins are named according to their density: very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL). Most cholesterol is transported by LDL.The liver secretes VLDL, which is converted to LDL in the bloodstream. The cholesterol on LDL is used to form membranes in cells throughout the body; deposits of LDL cholesterol in the arterial walls initiate the formation of plaques.
HDL also carries cholesterol in the blood; however, HDL has the beneficial capacity of picking up cholesterol from cells and atherosclerotic plaques and bringing it back to the liver for reprocessing or excretion. Therefore, HDL cholesterol is often referred to as "good" cholesterol, because it clears cholesterol from the arteries, while LDL cholesterol has been called "bad" because it deposits cholesterol in the arteries. Because elevated cholesterol levels contribute to the development of atherosclerosis, reducing cholesterol levels can help prevent coronary heart disease and heart attacks.
The blockage that ultimately triggers a heart attack is most often a blood clot that forms at a site where a coronary artery has developed atherosclerosis. This involves the formation of deposits called plaques within the walls of arteries. The plaques are composed of cholesterol-laden foam cells, smooth muscle cells, fibrous proteins, and calcium. As the plaques build up, the arterial walls thicken and narrow. Increased total and LDL cholesterol levels boost the risk of coronary heart disease by increasing the amount of cholesterol deposited within the walls of the arteries.
Symptoms of coronary heart disease, including angina, result when an advanced plaque narrows a coronary artery so much that it hinders blood flow to the heart. Plaque deposits also roughen arterial walls and make it easier for a blood clot to form along their surface. Complete blockage of a coronary artery by a clot can cause a heart attack. A portion of a clot can also break loose from its place of origin and cause a heart attack by lodging in a narrower section of the artery or in a smaller artery supplying blood to the heart.