Folic acid, also known as folate, folacin, and pteroylmonoglutamate, functions together with vitamin B12 in many body processes and is critical to cellular division because it is necessary for DNA synthesis. Without folic acid, cells do not divide properly. In the case of folic acid deficiency, all cells of the body are affected, but it is the rapidly dividing cells, such as red blood cells and cells of the gastrointestinal and genital tracts, that are affected the most. Folic acid is critical to the development of the nervous system of the fetus, and deficiency of folic acid during pregnancy has been linked to several birth defects, including neural tube defects such as spina bifida. Folic acid, vitamin B12, and betaine also function to reduce body concentrations of homocysteine, an intermediate in the conversion of the amino acid methionine to cysteine. A higher-than-average homocysteine level has been implicated in a variety of conditions, including atherosclerosis and osteoporosis. Homocysteine is thought to promote atherosclerosis by directly damaging the arteries as well as reducing the integrity of the vessel walls. In osteoporosis, elevated homocysteine levels lead to a defective bone matrix by interfering with the proper formation of collagen, the main protein in bone.
Folic acid received its name from the Latin word folium, meaning "foliage," because it is found in high concentrations in green leafy vegetables, such as spinach, kale, beet greens, and Swiss chard. Other good sources of folic acid include whole grains, legumes, asparagus, broccoli, and cabbage.