Cholesterol. Surface maps (wire-frame and colour-coded) of the electrostatic potential around a cholesterol molecule (C27. H46.O). Orange areas are due to carbon atoms, yellow areas due to hydrogen atoms, and the red area (lower left) is due to the oxygen atom. Cholesterol is a lipid, a fat-like substance, though chemically it is a sterol, a type of alcohol. It is an important cell chemical, and plays a crucial role in the synthesis of bile salts and hormones, and in transporting fats in the bloodstream. High blood levels of cholesterol are thought to raise the risk of atherosclerosis, the build-up of fatty deposits on artery walls. This is a major cause of heart attack and stroke.