Ups and downs of folic acid fortification

During our reproductive years, extra folic acid is essential. After that, it may be too much.

Folic acid is a synthetic form of folate, a B vitamin found naturally in various fruits, vegetables, and legumes. We need folate to produce and maintain new cells (in particular, red blood cells) and to keep nerve cells functioning properly.

It also helps prevent DNA changes that may lead to cancer. In the body, folic acid and naturally occurring folate are identical in their actions, but the bioavailability of folic acid is somewhat higher than that of folate.

There's abundant evidence that women who take folic acid supplements during the periconceptual period (just before conception and throughout the first trimester) can prevent neural tube defects such as spina bifida in their babies.

That explains the drive for folic acid fortification of grain and cereal products, which became mandatory in the United States and Canada in 1998. (Voluntary fortification was well under way before then.)

Around the same time, health officials boosted the recommended daily adult intake of folic acid to 400 micrograms (mcg). And women of childbearing age were advised to get at least 400 mcg of folic acid per day as part of a healthy diet including foods naturally high in folate and fortified foods.

At the time, it was estimated that fortification would contribute about 100 mcg of folic acid per day to the average diet.

Although the main reason for adding folic acid to the food supply was to prevent neural tube defects, health experts thought there might be benefits for others besides pregnant women and their children. Folic acid and vitamins B6 and B12 help keep homocysteine in check.

Homocysteine is an amino acid that has been associated with heart disease, stroke, dementia, and Alzheimer's disease when found in the blood at high levels.

The hope was that increased folic acid intake would help reduce homocysteine levels and possibly the risk of cardiovascular disease. Epidemiological and animal studies suggested that it might also help prevent certain forms of cancer, particularly colorectal cancer.

In Harvard's long-term Nurses' Health Study, for example, women who got adequate folic acid were less likely to develop colon cancer and, among those who drank alcohol, breast cancer.

Effects of folic acid fortification

In countries that require folic acid fortification, including the United States and Canada, the rate of neural tube defects has fallen by 25% to 50%. Other factors have probably contributed to this effect, such as increased use of prenatal multivitamins, ultrasound screening, and public health programs, but fortification has clearly played an important role.