Niacin is nicotinic acid or 3-carboxy-pyridine. Niacin is a vitamin. A deficiency in niacin causes pellagra, a disease that begins with dermatitis and leads to insanity and death. Bread companies add niacin to their bread. Niacin is essential to the body since it occurs as niacinamide in coenzyme NAD⁺ (nicotinamide adenosine dinucleotide).