A water-soluble vitamin belonging to the vitamin B family, which occurs in many animal and plant tissues, with antihyperlipidemic activity. Niacin is converted to its active form niacinamide, which is a component of the coenzymes nicotinamide adenine dinucleotide (NAD) and its phosphate form, NADP. These coenzymes play an important role in tissue respiration and in glycogen, lipid, amino acid, protein, and purine metabolism. Although the exact mechanism of action by which niacin lowers cholesterol is not fully understood, it may act by inhibiting the synthesis of very low density lipoproteins (VLDL), inhibiting the release of free fatty acids from adipose tissue, increasing lipoprotein lipase activity, and reducing the hepatic synthesis of VLDL-C and LDL-C. or A form of niacin (vitamin B3) that the body needs in small amounts to function and stay healthy. Niacinamide is found in many plant and animal products and in dietary supplements. It is water-soluble (can dissolve in water) and must be taken in every day. Niacinamide may be used to treat diabetes and certain skin conditions and is being studied in the treatment of some types of cancer. It may increase blood flow to cancer cells and block certain enzymes they need to repair damage to their DNA. This may make cancer cells easier to kill with radiation therapy and chemotherapy. Niacinamide is a type of radiosensitizing agent and a type of chemosensitizing agent. Also called nicotinamide.