Folic acid consumption has declined in the U.S.

NEW YORK (Reuters Health) - While folic acid consumption by women of childbearing age in the U.S. increased substantially after the fortification of enriched-grain foods was mandated in 1998, it has since dropped, according to an analysis by researchers at the University of Florida in Gainesville.

Folic acid, also referred to as folate, is a type of B vitamin that helps the body make healthy new cells. A folic acid deficiency before or during pregnancy can cause major birth defects.

However, folic acid levels have dropped the least in women who have the highest risk of being folic acid-deficient, so the impact on the risk of having infants born with serious brain and spinal abnormalities, referred to as neural tube defects, is likely to be moderate.

Drs. Jesse F. Gregory and Eoin P. Quinlivan note that after the 1998 mandate, cereal-grain products were widely over-fortified (up to 160 percent to 175 percent of the required amount of folic acid), so folic acid derived from fortified foods was almost double what had originally been envisioned.

More recently, the physicians report, fortification with folic acid appears to have dropped to levels closer to those established by the U.S. Food and Drug Administration. Coupled with the popularity of low-carbohydrate diets, this probably accounts for the decreases in folic acid concentrations found in the National Health and Nutrition Examination Survey between 1999 and 2004.

The researchers used data from 11 previous studies to assess the changes in folic acid levels and to estimate the effect on the occurrence of neural tube defects occurrence. Their report appears in the American Journal of Clinical Nutrition.

The women with the lowest folic acid levels had the largest increases in folic acid concentrations immediately following the fortification mandate and the smallest decreases more recently.

The researchers also estimate that the number of women who had a risk of consuming too much folic acid, perhaps as high as 10 percent, has "decreased significantly."

Estimates of the risk of neural tube defects, which dropped by as much as 43 percent after fortification, may have rebounded between 1999 and 2004 by 4 to 7 percent. This is less than would be seen if there had been a uniform reduction in folic acid intake.

"There is probably less of a protective effect against neural tube defects than there was when folic acid intake was higher," Gregory told Reuters. "This would be balanced against lower risks of the proposed adverse effects. All nutrition interventions have risks and benefits."

For example, he noted that colorectal cancer has been associated with both folic acid insufficiency and excessive folic acid levels, and some studies have found that "the neurological effects of low vitamin B12 can be exacerbated by excessive intake of folic acid."

In addition to fortified foods, other sources of folic acid are vitamin supplements and leafy green vegetables, fruits, dried beans, peas and nuts.

SOURCE: American Journal of Clinical Nutrition, December 2007.