Lipoproteins and cholesterol

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Lipoproteins and cholesterol

"Bad" cholesterol: Low-density lipoprotein (LDL) contains a smaller proportion of protein than other lipoproteins. LDL consists mostly of cholesterol (75%), and the majority of the cholesterol circulating in your blood (60% to 75%) is found in LDL. As a result, LDL accounts for the majority of the cholesterol in your total cholesterol measurement.

A certain level of LDL in your blood is normal and healthy because LDL is responsible for delivering cholesterol to the parts of your body that need it. Excess LDL, however, causes a buildup of cholesterol in the walls of your arteries, contributing to the development of atherosclerosis.

"Good" cholesterol: High-density lipoprotein (HDL) contains a much larger proportion of protein than LDL does. HDL carries about 20% to 30% of the cholesterol in your blood. Unlike LDL, the job of HDL is to remove excess cholesterol from your cells and the walls of your arteries and then transport the cholesterol back to your liver for disposal. While HDL has other roles, not all of which are fully understood, you can think of HDL as a positive force in the entire lipoprotein cycle. Overall, HDL is "good" because it may actually slow or even reverse the development of atherosclerosis.

Triglycerides: Triglycerides combine with cholesterol and protein to make lipoproteins. Your body uses and stores fat nutrients as triglyceride. In addition to processing triglyceride from dietary fat, your body also produces triglyceride in your liver.

The way your body processes triglyceride-rich lipoproteins, such as chylomicrons and VLDL, directly affects the making of cholesterol-rich lipoproteins that cause high cholesterol, such as LDL. For example, when there are high levels of triglyceride to be processed because of a diet high in saturated fat, the body produces more LDL. This helps to explain why a diet high in saturated fat can significantly increase your LDL level, your total cholesterol, and your risk of atherosclerosis.

Chylomicrons: When you eat foods that contain fat, enzymes in your small intestine break them down into small particles of triglyceride. Your small intestine then absorbs these particles and combines them with small amounts of cholesterol, protein, and phospholipid to form lipoproteins called chylomicrons. The chylomicrons circulate in the bloodstream and deliver triglycerides to your cells for immediate use or for storage.

Very low-density lipoprotein (VLDL): These lipoproteins are "very low-density" because they contain very little protein. VLDL is composed largely of triglyceride but also carries 10% to 15% of the cholesterol in your blood. The main purpose of VLDL is to distribute the triglyceride produced by your liver.

Credits

Last updated:	July 20, 2006
Author:	Ralph Poore
Reviewed By:	Caroline S. Rhoads, MD - Internal Medicine, Neil J. Stone, MD, FACC, FACP - Internal Medicine, Cardiology
Editors:	Kathleen M. Ariss, MS, Terrina Vail