Also known as vitamin PP, niacin is a coenzyme in the body for a variety of enzymes that do not require oxygen dehydrogenation. When a deficiency of niacin is present, mange can develop, mainly in the form of dermatitis, diarrhea, and dementia. Dermatitis is often symmetrical and appears on exposed areas. Dementia is the result of degeneration of nerve tissue. Recently niacin has been used clinically as a cholesterol-lowering agent. Niacin inhibits lipolysis in adipose tissue, thereby inhibiting the mobilization of free fatty acids, which can lead to a decrease in the synthesis of very low-density lipoproteins (VLDLs) in the liver, thus having a cholesterol-lowering effect. Nitric acid is widely available in nature, and the liver can convert tryptophan into nitric acid, but the conversion rate is relatively low because tryptophan is an essential amino acid, and the human body mainly takes in nitric acid from food.