Niacin is vital to oxidation of all living cells, where, as a functional group of the coenzymes NAD and NADP, it is involved in the release of energy from carbohydrate, fat and protein, and the synthesis of proteins, fats, and pentoses for nucleic acid formation. Tissues with a high respiration rate, such as the central nervous system, are therefore the most extensively affected by deficiency.

Nicotinic acid also has a pharmacological role in which it is an effective hypolipidaemic agent. It is particularly effective, at levels of daily consumption of the order of 1 g, in lowering the concentrations in the blood of low and very low density protein (LDL and VLDL) cholesterol and in increasing the concentration of high density lipoprotein (HDL) cholesterol.