It’s only a little, but it can do a lot. Just 400 μg of folic acid—the technical name for vitamin B9—taken prenatally can reduce the incidence of birth defects by as much as 70 percent, as well as lowering the risk of miscarriage. The benefits continue beyond birth, as well. Children need folate to grow. In adults, it makes red blood cells, helps prevent stroke, reduces the likelihood of stomach cancer and protects the eyes from age-related macular degeneration, a type of progressive blindness.
It’s even more important for fetal development. Without enough folic acid, the spine and back won’t properly develop. This can result in what’s called a neural tube defect, a class of birth defects including anencephalopathy and spina bifida. Spina bifida is a condition in which the vertebrae do not fully close around the spinal cord, which may the protrude. This can result in leg weakness, orthopedic problems, incontinence, and other symptoms.
Insufficient folic acid can cause other pregnancy complications as well. Women who take folic acid supplements during the 12 months before pregnancy are half as likely to have premature labor. Another reason to be sure to get enough folic acid in advance of pregnancy is that the first four weeks after conception are the critical period for avoiding birth defects after the baby arrives. Even would-be dads can benefit—folic acid deficiency in men is linked with infertility and low sperm count.
Fortunately, folate is readily available in the diet. It is found naturally in asparagus, bananas, beans, leafy green vegetables such as spinach, lemons, liver mushrooms, okra, oranges, organ meats, and yeast. In addition, in the United States, most flour is fortified with folic acid, meaning most baked goods—whether commercial or made at home—have it.
People who are still worried about a deficiency, or for whom deficiency would by particularly devastating, can take supplements, which are available over the counter. People at risk for deficiency—smokers, drinkers, people with kidney or liver disease—should definitely supplement. There is little danger from too much folic acid. The body can store enough folate to last as long as seven weeks, and is very efficient at processing and expelling what it doesn’t need.