Niacin (also known as vitamin B3, nicotinic acid and vitamin PP) is an organic compound with the formula C6H5NO2 and, depending on the definition used, one of the 40 to 80 essential human nutrients. Niacin is one of five vitamins (when lacking in human diet) associated with a pandemic deficiency disease: niacin deficiency, vitamin C deficiency, thiamin deficiency, vitamin D deficiency, vitamin A deficiency (night blindness and other symptoms).