Cholestrol is a waxy organic compound found in blood and all animal tissues.

It is a steroid, with molecular formula C₂₇H₄₆O, containing four rings in its structure. Cholesterol is essential to life; it is a primary component of cell membranes and a starting or intermediate material from which the body makes bile acids, other steroid hormones, and vitamin D. It is made in the liver and some other organs, in greater or lesser amounts depending on the amount recently consumed in the diet. It circulates in the blood in compounds called lipoproteins, since it is not water-soluble alone. Excess cholesterol in the blood forms deposits in arteries (see arteriosclerosis), which can lead to coronary heart disease. Michael Brown (born 1941) and Joseph Goldstein (born 1940) won a Nobel Prize in 1985 for their work in discovering this process. Since the body makes cholesterol from fats, blood cholesterol cannot be reduced by limiting only the amount of cholesterol in the diet; the amount of fat, especially saturated fat (see saturation, fatty acid) must also be reduced. See also triglyceride.