Niacin, or nicotinic acid, is a member of the water-soluble vitamin B family and, for the most part, functions as part of two important coenzymes. Both enzymes play vital roles in a number of metabolic pathways, in particular, those pathways concerned with cellular respiration (the process by which tissue cells "burn" carbohydrates and proteins in order to release energy) and, to a lesser extent, those pathways involved in the synthesis of fatty acids and steroids.

A deficiency of niacin causes pellagra, a serious disease which has plagued mankind for centuries, in most cases striking people whose diet consists mainly of corn and cornmeal. Until fairly recently, pellagra was a major health problem in the United States, especially in poorer rural areas. In the 1920s, in fact, pellagra not only killed thousands of people but pellagra patients filled both hospitals and (because mental confusion was one of its symptoms...