Cholesterol and HD

An investigation into how HD affects cholesterol homeostasis

HDL and LDL

Most people have heard of a distinction between two types of cholesterol: HDL and LDL. HDL stands for high-density lipoprotein, while LDL stands for low-density lipoprotein. HDL is commonly referred to as "good" cholesterol, while LDL is called "bad" cholesterol. More precisely, HDL and LDL are not simply different types of cholesterol, but rather alternative groups of lipids and proteins that transport the cholesterol throughout the body in the bloodstream. Molecules such as HDL and LDL are needed to carry cholesterol because it is a hydrophobic molecule and therefore cannot dissolve in blood and travel through the bloodstream on its own.

But if HDL and LDL are just alternative cholesterol carrier molecules, why is one considered good and the other bad? Medical studies have noted that high levels of LDL are associated with an increased risk of cardiovascular disease, whereas high levels of HDL are associated with decreased risk of cardiovascular disease.

How exactly does HDL produce beneficial effects and LDL produce harmful effects? LDL is the major cholesterol carrier in the blood and is responsible for delivering cholesterol to cells in the body. High levels of LDL cholesterol in the blood contribute to the formation of plaque. Plaque is a thick, hard deposit of fat, cholesterol and other substances that clogs arteries and causes atherosclerosis. If arteries become severely clogged with plaque, oxygen-carrying blood may not reach be able circulate around the body- which can lead to heart attack or stroke. Approximately one fourth of blood cholesterol is carried by HDL. HDL is believed to protect against atherosclerosis by carrying cholesterol away from the blood (so it cannot contribute to plaque formation) or even removing excess cholesterol from plaque already built-up in the arteries. HDL usually delivers cholesterol to the liver or endocrine cells, where it will be used in the synthesis of steroids or bile salts, and ultimately removed from the tissue and bloodstream.

Last Modified: 07/07/2007

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