Folic acid. A pill of folic acid, one of the B vitamins, on a woman's hand next to the pill bottle. Folic acid is an important supplement in pregnancy. It is necessary for the activities of enzymes involved in the manufacture of nucleic acids (cell genetic material). It therefore plays an important role in growth, reproduction, the functioning of the nervous system, and in red blood cell production. Folic acid is found in leafy green vegetables, peas and beans, mushrooms, egg yolk and liver. A deficiency of folic acid can lead to anaemia, poor growth in children, and sores around the mouth.