cholesterol

White, crystalline sterol found throughout the body, especially in fats, blood, nerve tissue, and bile; it is also provided in the diet by foods such as eggs, meat, and butter. A high level of cholesterol in the blood is thought to contribute to atherosclerosis (hardening of the arteries).

Cholesterol is an integral part of all cell membranes and the starting point for steroid hormones, including the sex hormones. It is broken down by the liver into bile salts, which are involved in fat absorption in the digestive system, and it is an essential component of lipoproteins, which transport fats and fatty acids in the blood. Low-density lipoprotein cholesterol (LDL-cholesterol), when present in excess, can enter the tissues and become deposited on the surface of the arteries, causing atherosclerosis. High-density lipoprotein cholesterol (HDL-cholesterol) acts as a scavenger, transporting fat and cholesterol from the tissues to the liver to be broken down. The composition of HDL-cholesterol can vary and some forms may not be as effective as others. Blood cholesterol levels can be altered by reducing the amount of alcohol and fat in the diet and by substituting some of the saturated fat for polyunsaturated fat, which gives a reduction in LDL-cholesterol. A 1999 US study of children with high levels of cholesterol found no evidence that controlling cholesterol levels through diet is harmful. Another 1999 US study suggested that cholesterol-lowering drugs are as beneficial for older men and women as they are for the middle-aged. HDL-cholesterol can be increased by exercise.