According to 2010 information from the Centers for Disease Control and Prevention, one in every six adults in the United States suffer from high total blood cholesterol, defined as a level of 240 mg/dL or greater. This doubles their risks for heart disease over those with optimal cholesterol levels. Because cholesterol must bind to specialized proteins known as lipoproteins to travel through the blood and reach the cells, it exists in several different forms. To fully understand your total cholesterol profile and how it impacts your risk for heart disease, you must understand the difference between LDL and HDL cholesterol.
Structure
Because cholesterol is fatty and blood is watery, they do not mix. To travel in the bloodstream, the cholesterol made in the liver combines with water-soluble proteins, forming a "package" called a lipoprotein. Low-density lipoprotein, or LDL, and high-density lipoprotein, or HDL, differ in their structures. LDL is a large molecule that contains less protein and more fat. High density lipoprotein is a small molecule that contains more protein and less fat, making it denser.
Function
The cells in the liver produce approximately 75 percent of all the cholesterol in the body. LDL binds to the majority of this cholesterol from the liver and carries it to the cells. Its low density allows the cholesterol to remain in the bloodstream. HDL, which binds to only 1/4 to 1/3 of all cholesterol, picks up excess cholesterol from tissues in the body, including the blood vessels, and carries it back to the liver. The liver then breaks the cholesterol down and excretes it from the body with the waste. These unique functions give LDL the distinction of "bad" cholesterol and HDL a label of "good" cholesterol.
Impact
Because LDL keeps cholesterol within the blood vessels, as cholesterol levels increase, the amount in the blood vessels also increases. Cholesterol is attracted to areas of damage on the blood vessel walls. The more cholesterol in the blood vessel, the more there is to attach to the walls. This leads to the formation of plaque -- a substance consisting of fat, cholesterol, calcium and other waste particles. The buildup of plaque causes the blood vessels to thicken and become hard, which interferes with the flow of blood. When this occurs in the arteries leading to the heart, it causes coronary artery disease, the most common form of heart disease. In addition, pieces from the plaque can break off and cause a heart attack or stroke. Because HDL picks up excess cholesterol and removes it from the body, it helps to prevent or slow the formation of plaque and reduces the risk for heart disease.
Levels
Due to the unique function of LDL and HDL, the desired levels also differ. You want to keep LDL levels as low as possible to keep your risk of heart disease low. The Heart Lung and Blood Institute reports the optimal level for LDL cholesterol as 100 mg/dL or lower. The protective effects of HDL mean the higher the level, the better. Men should maintain a HDL level of at least 40 mg/dL, while women should maintain their HDL level at 50 mg/dL or higher. HDL levels of 60 mg/dL or higher provide protection against heart disease.
References
- American Heart Association: What Your Cholesterol Levels Mean; February 2011
- National Heart Lung and Blood Institute: What is High Blood Cholesterol?; September 2008
- American Heart Association: Good vs. Bad Cholesterol; July 2010
- Centers for Disease Control and Prevention; America's Cholesterol Burden; February 9, 2010
