Cholesterol is transported in blood as part of a package called a lipoprotein. LDL is low-density lipoprotein. Cholesterol carried by an LDL particle is called LDL cholesterol. HDL is high-density lipoprotein. Cholesterol carried by an HDL particle is known as HDL cholesterol.

Every cell in the body requires cholesterol. Low-density lipoprotein transports cholesterol from the liver through the blood to the cells. However, if the blood contains too much LDL cholesterol, the cholesterol collects in the inner walls of the arteries, helping to form a deposit called plaque. The plaque, which contains fat, calcium and fibrous material as well as cholesterol, may bulge into the cavity of the artery and reduce blood flow. Bits of the plaque may break off and travel to other blood vessels. Blood flowing over the surface of broken plaque can form clots. Plaque may harden and make the artery walls stiffer, so it’s more difficult for the arteries to expand and contract in response to the heartbeat. This hinders blood flow.

Coronary arteries supply the heart muscle with oxygen and nutrients. If a coronary artery becomes blocked by plaque or blood clots, a heart attack may happen and a portion of the heart muscle may die. If a carotid artery going up the neck to the brain is blocked, the brain won’t receive enough oxygen and a stroke may result. Peripheral Artery Disease, also called Peripheral Arterial Disease, is caused by reduced blood flow to the legs (or sometimes to the arms or other body parts) due to narrowed or blocked arteries. LDL cholesterol is known as the “bad” cholesterol because of the health problems that it can cause.

High-density lipoproteins pick up cholesterol from the arteries and transport it to the liver, which breaks the cholesterol down. HDL cholesterol is known as the “good” cholesterol because it reduces the risk of heart attacks, strokes and other health problems caused by blocked arteries.