water-soluble vitamin of the B complex that is essential in animals and plants for the synthesis of nucleic acids. Folic acid was isolated from liver cells in 1943.

The vitamin has a wide variety of sources in the human diet, including leafy green vegetables, citrus fruits, cereals, beans, poultry, and egg yolks. A deficient intake of folic acid can impair the formation of red blood cells, resulting in folic acid deficiency anemia. Folic acid deficiency anemia may be a result of malabsorption disorders such as celiac disease and tropical sprue. Pregnant women with an insufficient intake of folic acid are more likely to give birth prematurely or to deliver babies with low birth weight or with neural tube defects. The sulfa drugs achieve their antimicrobial effects by interfering with the production of folic acid within bacteria.