Cholesterol is the principal sterol of vertebrate animals, embedded in every plasma membrane and concentrated in blood, liver, nerve tissue, brain, and animal fats. The body uses it as the starting material for bile acids and steroid hormones, and because we synthesize it ourselves, it is not an essential dietary nutrient. High blood levels, however, are firmly linked to atherosclerosis and coronary heart disease, which is why the food industry markets cholesterol-reduced dairy products and eggs. Dietary guidance has grown more nuanced, but cholesterol remains the benchmark lipid in nutrition labelling and cardiovascular risk assessment.