Lipoproteins and cholesterol
Roles of lipoproteins and triglycerides Type
What they do
Low-density lipoproteins (LDL)
- Deliver cholesterol to your body
- In excess, lead to a buildup of cholesterol in the walls of your arteries
High-density lipoproteins (HDL)
- Prevent harmful buildup of cholesterol in your arteries
Triglycerides
- Affect production of cholesterol-rich lipoproteins that cause high cholesterol
- Store fat nutrients
- Increase the ability of blood to clot
Chylomicrons
- Carry dietary fat from the intestine to the liver
- Deliver dietary fat in the form of triglyceride to muscle tissue cells
- Deposit excess triglyceride in fat (adipose) tissue
Very low-density lipoproteins (VLDL)
- Distribute triglyceride made in the liver to muscle cells
- Deposit excess triglyceride in the fat tissue
- In excess, can contribute to buildup of cholesterol in your arteries
"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.
| Author: | Robin Parks, MS | Last Updated: July 20, 2006 |
| Medical Review: | E. Gregory Thompson, MD - Internal Medicine Robert A. Kloner, MD, PhD - Cardiology | |
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