Cholesterol is a waxy, fat-like substance that is found in all cells. Dietary cholesterol is not required because the body sufficiently produces its daily requirement.
Cholesterol is essential for the production of hormones, vitamin D and substances that aid in food digestion. Because blood is watery and cholesterol is fatty, the two do not mix, much like water and oil. Cholesterol can only travel in the bloodstream in small packages, called lipoproteins. Lipoproteins are made of fat (lipid) on the inside and proteins on the outside. Two kinds of lipoproteins (LDL and HDL) carry cholesterol throughout your body. It is important to have healthy levels of both.
Low-density lipoprotein (LDL) cholesterol is sometimes called bad cholesterol. High LDL cholesterol leads to a buildup of cholesterol in arteries. The higher the LDL level in your blood, the greater chance you have of getting heart disease.
High-density lipoprotein (HDL) cholesterol is sometimes called good cholesterol. HDL carries cholesterol from other parts of your body back to the liver. The liver removes the cholesterol from your body. The higher your HDL cholesterol level, the lower your chance of getting heart disease.
Too much cholesterol in the blood, or high blood cholesterol, can be dangerous. People with high blood cholesterol have a greater chance of acquiring heart disease. High blood cholesterol on its own does not cause symptoms, as a consequence, many people are unaware they are at risk.
Cholesterol can build up on the artery walls (blood vessels that carry blood from the heart to other parts of the body). This buildup of cholesterol is called plaque. Over time, plaque can cause narrowing of the arteries, a condition called atherosclerosis, or hardening of the arteries.
The illustration shows a normal artery with normal blood flow (Figure A) and an artery containing plaque buildup (Figure .