Folic acid, or vitamin B9, is part of cell growth. It is essential in building and repairing DNA molecules in the body. It is one of the nutrients that makes it possible for children to grow. In adults, it helps make red blood cells and avoid anemia. There are some indications that folic acid can help prevent stroke. Folate may help improve mood in people with depression. Nutritional supplements containing folic acid may help lower the risk of a type of progressive blindness called age-related macular degeneration.
Pregnant women particularly need folic acid. Enough folic acid—which for women who are or expect to be pregnant means 400 μg per day—can reduce birth defects by more than two-thirds. Folate helps the spine and back of the fetus develop properly, minimizing miscarriages and a class of birth defect, called a neural tube defect, that includes spina bifida and anencephaly. Folate also helps prevent congenital heart defects and cleft lips in the fetus. Low levels of folic acid can even make it harder for a woman to get pregnant in the first place.
Because folic acid is water-soluble, the body is actually quite efficient at handling an excess. Too little folic acid is therefore a rather more significant danger than too much. However, unusually high levels of folate can make it difficult to detect dangerously low levels of iron and vitamin B12. Deficiency is itself rare, though, because the nutrient is quite common and the body typically keeps a reserve of as much as seven weeks’ worth. Nonetheless, kidney or liver disease, excessive alcohol consumption, exposure to cigarette smoke, and poor diet can lead to a deficiency. In addition to anemia, this deficiency can lead to depression, confusion or dementia, diarrhea and excessive weight loss, cardiovascular disease, and a condition called glossitis in which the tongue swells, interfering with breathing.
Fortunately, a deficiency is easy to reverse. Folic acid supplements are available over the counter, and it’s difficult to inadvertently omit from the diet. Folic acid is found in the leafy green vegetables from which the name is derived, as well as asparagus, okra, bananas, beans, oranges, lemons, organ meats, mushrooms and even yeast, Furthermore, Federal law in the United States that it be added to flour, and so many baked goods have folic acid in them.