Nicotinic acid is a water-soluble vitamin found in a variety of foods, but is most concentrated in legumes, lean meats, eggs, and enriched breads and cereals. More stable than most other vitamins, little nicotinic acid is lost through cooking or exposure to water. The United States Food and Drug Administration’s Recommended Dietary Allowance (RDA) of the vitamin is approximately 20 milligrams per day for adults. Most studies show that the majority of Americans meet or exceed this requirement, which can also be supplemented by intake of the amino acid tryptophan, a precursor of nicotinic acid.