A deficiency of folic acid after birth causes a kind of anemia, namely, megaloblastic anemia in which there is a paucity of red blood cells and those that are made are unusually large and immature (so-called blast cells).
Lack of adequate folic acid during pregnancy was first found to increase the risk for the baby to have a birth defect involving the spinal cord and brain -- a neural tube defect such as spina bifida (meningomyelocele) or anencephaly.
The association was then investigated between the mother's use of drugs that act as folic acid antagonists in the first trimester of pregnancy and the birth of a child with a congenital malformation (birth defect). It was found that folic acid antagonists increased the risk not only of neural tube defects but also of congenital heart malformations, cleft lip and palate, and urinary tract defects. Folic acid, it now is clear, reduces the risks for a remarkably broad gamut of birth defects.
In order for folic acid to be effective in preventing these birth defects, the vitamin must be consumed every day beginning before conception and continuing through the first three months of pregnancy. Educating women (and their doctors) about the importance of folic acid is going to require a major effort. According to one study, only 10% of women know that folic acid should be taken before pregnancy.
An adequate intake of folic acid appears important to the health of arteries, reducing the risk of second heart attacks and strokes (it may do so by lowering the level of homocysteine). Folic acid also may lower the risk of stomach cancer.