Cholesterol is essential to life. Every cell in your body requires cholesterol in its membranes. Cholesterol is also the starting material from which your body makes vitamin D, steroid hormones and bile acids for digestion. Cholesterol is one member of a large family of chemical compounds known as lipids. The more common name for lipids is fats. There are five major groups of lipids:
- sterols (cholesterol, some hormones)
- fat-soluble vitamins (A,E,K)
- fatty acids (saturated or unsaturated)
- glyceryl esters (dietary and body fat)
- sphingolipids (components of cell membranes)
Cholesterol in blood is usually described as serum or plasma cholesterol. Serum or plasma is the watery part of blood remaining after red and white blood cells have been removed. The pool of cholesterol in blood contains cholesterol from two sources: outside the body (foods), and manufactured inside the body. Cholesterol is made primarily in the liver and intestine from fragments of fats, proteins, and carbohydrates. Cholesterol is withdrawn from blood for use in cell membranes; in tissues such as heart, liver or muscle; and for making hormones and bile acids.
Cholesterol, being a lipid, does not mix with water. In order to travel through the blood, a watery system, cholesterol is coated with protein. The resulting macro-molecule is a lipoprotein. Lipoproteins are carriers for transporting cholesterol throughout the body. Five major classes of lipoproteins have been identified. Two (LDL and HDL) are commonly measured by blood tests and are linked to risks for coronary heart disease.
- Low density lipoprotein (LDL) is composed largely of lipid (triglyceride and cholesterol) with only a small amount of protein. LDL-cholesterol is generally on its way to be deposited in tissues, including the artery wall. Triglycerides are the most common type of fat in your body. They’re also a major energy source. They come from food, and your body also makes them.
- High density lipoprotein (HDL) contains less cholesterol and more protein. HDL-cholesterol is probably on its way out of the body pool of cholesterol. For example, it may be on its way to the liver where some of it will be converted into bile acids. Both cholesterol and bile acids are secreted into the intestine.
Unlike fats, proteins, and carbohydrates, cholesterol cannot be used for energy. Small amounts of cholesterol can be used up making hormones and vitamin D. However, the major products made from cholesterol are bile acids. Formed in the liver, bile acids are secreted into the intestine where they help digest fat. Some of the bile acids are excreted with waste from the digestive tract. Most of the bile acids are recycled and reused. The body excretes approximately 1,000-1,400 mg cholesterol each day. That’s three to four times the 300 milligram USDA (U.S. Department of Agriculture) recommended limit for dietary cholesterol. The liver has mechanisms which regulate cholesterol production in response to our dietary cholesterol intake. The more dietary cholesterol that is consumed, the less the liver makes.
Risk categories for LDL-Cholesterol
- less than 130 mg/dL, average check in 5 years
- 130-160 mg/dL, moderate check every year
- 161-189 mg/dL, high diet therapy for 6 months; if little change, begin drug therapy
- 190 mg/dL and over extreme begin both diet and drug therapy at once
Prepared by Elisabeth Schafer, Ph.D., extension nutrition
specialist and Diane Nelson, extension communications specialist