What it is
Folic acid (vitamin B9) is one of the essential water-soluble vitamins in the B- complex family (others include vitamins B6 and B12). “Folate” refers to the form of vitamin B9 that occurs naturally in food, as opposed to a manufactured supplement.

Where it comes from
The best dietary sources of folate are dark green leafy vegetables, brewer’s yeast, orange juice, fortified cereals and grains, and broccoli. Virtually all multivitamin-mineral supplements include folic acid; it is also available as a stand-alone supplement or as part of a B-complex supplement. Research shows that folic acid supplements boost blood levels of this vitamin better than food sources (BJOG: An International Journal of Obstetrics and Gynaecology, 2000, vol. 107, no. 2).

Why it’s used
Even though it is one of the most recently discovered vitamins, folic acid is crucial to almost every aspect of health. All women of childbearing age, and especially pregnant women, should take folic acid because it reduces the risk of a birth defect called neural tube defect. Folic acid is also an effective way to lower high homocysteine levels, a risk factor for heart disease and stroke that is viewed increasingly as more important than cholesterol. One common form of anemia can respond quickly to folic acid, along with vitamin B12.

How it works
Folic acid takes center stage during times of rapid growth, such as infancy and pregnancy, because this vitamin is necessary for cells to replicate and grow through its role in making DNA and RNA (the blueprint for cells). Folic acid is also crucial to red blood cells, which are constantly regenerating. In addition, folic acid serves as a cofactor for enzymes that lower levels of homocysteine, an amino acid in the blood, helping the enzymes to process it into a harmless substance. And folic acid guards against changes to DNA that could otherwise lead to cancer.

Scientific support
Too little folic acid in the first few weeks of pregnancy—often before a woman knows she is pregnant—increases the risk of bearing a child with a neural tube defect, such as spina bifida or anencephaly, conditions in which the embryonic neural tube, which forms the future brain and spinal column, fails to close properly. Supplementing with folic acid in the three months before and after conception could prevent 50 percent to 70 percent of the approximately 2,500 babies born in the United States each year with a neural tube defect (Morbidity and Mortality Weekly Report, 2004, vol. 53, no. 17). Pregnant women should take folic acid throughout their pregnancy to keep the baby developing and growing properly.

Folic acid supplements can also help stave off heart disease, researchers have found, by lowering homocysteine levels (Nutrition, 2000, vol. 16, no. 2). With too much homocysteine, blood does not flow as well through the vessels. In addition, homocysteine can damage the coronary arteries and increase the chances that a clot will form, triggering a heart attack. By decreasing homocysteine levels, folic acid reduces the risk of heart disease and stroke.

Given the importance of folic acid, it is not surprising that since 1998 the Food and Drug Administration has required that the U.S. flour supply be fortified with folic acid. This fortification program has been successful, as evidenced by a lower incidence of neural tube defects and improved homocysteine levels.

All women of childbearing age should take at least 400 mcg of folic acid daily to reduce the risk of birth defects. The same amount also lowers the risk of heart disease for adult men and older women.

For about $1, you can buy a month’s supply of 400 mcg folic acid pills. Most multivitamin-mineral supplements, which vary in cost, include folic acid (typically at the recommended 400 mcg dosage).

Safety issues
Being a water-soluble vitamin, any excess folic acid is excreted in urine. In fact, intakes hundreds of times greater than the recommended dose have not been shown to have toxic effects. Even so, consult with a health care provider if you take more than 1,000 mcg per day.

Oregon-based freelancer Victoria Dolby Toews, MPH, is the author of User’s Guide to Sexual Satisfaction (Basic Health Publications, 2003) and User’s Guide to Glucosamine and Chondroitin (Basic Health Publications, 2002).