Too much of a good thing

Folic acid deficiency during pregnancy has been linked to neural tube defects in newborns, and low intake of folic acid has been associated with depression and cardiovascular disease. There is some evidence that supplementing with folic acid might prevent Alzheimer’s disease and certain types of cancer, although other research suggests that excessive folic acid supplementation could increase the risk of colorectal cancer.

For most people, supplementing with folic acid is extremely safe, however, one danger in getting too much is that it can make it harder to diagnose a B12 deficiency. Left untreated, B12 deficiency can cause nerve damage that is sometimes permanent. In the current study, people who supplemented were actually less likely to be B12-deficient than people who did not use supplements, probably because their supplements provided some vitamin B12 as well as folic acid.

Getting it right

“Even though enriched cereal-grain products, ready-to-eat cereals, and supplements all contribute to total folic acid intakes, most US adults are unlikely to be getting too much folic acid,” said study co-author Dr. Robert Berry of the Centers for Disease Control and Prevention. “Only those whose supplements provide more than 400 mcg per day appear to be at risk of exceeding the upper level for daily folic acid intake.”

Here are some ways to get the right amount of folic acid:

• Eat healthy foods that provide folic acid, such as dark green lettuce, other greens, beans, lentils, and whole grains.
• Take a multivitamin that provides 400 mcg or less of folic acid per day. Although the science is inconclusive, some studies have found that regular use of a multivitamin/mineral supplement can prevent heart disease and slow the aging process.
• If you take supplements with more than 400 mcg of folic acid, make sure they also provide vitamin B12.
• If you are using high-dose folic acid therapeutically, consider asking your doctor to check your B12 status through a blood test that measures the methylmalonic acid level, especially if you are over 60 years old. The elderly have an increased risk of B12 deficiency, even if dietary intake is adequate.

(Am J Clin Nutr 2010;91:64–72)