Originally isolated from spinach leaves, folic acid derives its name from the Latin word folium, meaning "leaf." The water-soluble B vitamin is essential to the human body, playing a role in such important functions as red blood cell formation, growth and development, and maintenance of the central nervous system. Folic acid is believed to be especially important for pregnant women, and many doctors advise women of reproductive age to increase their intake of the vitamin to help deter neural tube defects, such as anencephaly and spina bifida, in newborns. Indeed, it is estimated that as many as 70 percent of some serious birth defects are preventable by taking as little as 400 micrograms of folic acid per day. Natural sources of folic acid include liver, yeast, most berries, leafy green vegetables, citrus fruits, soybeans, wheat, and rice.