BETHESDA, MD. — Two just-published studies in the American Journal of Clinical Nutrition powerfully validate a 1996 mandate to fortify enriched grains with folic acid. That was the conclusion of an editorial published in the same edition of the journal.

The editorial, "Getting folic acid nutrition right," was written by Irwin Rosenberg, senior scientist and director, Nutrition and Neurocognition Laboratory, Jean Mayer USDA HNRCA at Tufts University, Boston.

"These reports, which are based largely on National Health and Nutrition Examination Survey (NHANES) data for the 2003–2006 time period, show how the Food and Drug Administration (F.D.A.) models of exposure, which preceded the 1996 mandate that enriched flour be fortified with 140 micrograms of folic acid per 100 grams flour to prevent neural tube defect births, got the folic acid dose right," Dr. Rosenberg said. "This mandate increased folic acid exposure in women of childbearing age without excessive exposure to those beneficiaries and others in the population."

The studies examined folic acid intake in the United States, exploring the percentage of the population with daily intake above the 1,000 micrograms per day, which was set by the Institutes of Medicine as an upper limit.

Both studies gathered data using the National Health and nutrition Examination Survey (NHANES) 2003-2006. The first was published by a team led by Quanhe Yang, an epidemiologist from the Office of Public Health Genomics, Centers for Disease Control and Prevention, Atlanta.

In "Folic acid source, usual intake and folate and vitamin B-12 status in U.S. adults," estimated folic acid intake above the upper limit was explored. Intake was measured based on three major sources: enriched cereal grain products, ready-to-eat cereals and supplements.

The researchers found 2.7% of adults consumed more than the daily upper limit for folic acid.

"At current fortification levels, U.S. adults who do not consume supplements or who consume an average of less than 400 micrograms folic acid daily from supplements are unlikely to exceed the U.L. in intake for folic acid," Dr. Yang said.

The study found that for 42% of Americans, enriched grains are the only major source of folic acid in the diet. With the addition of R.-T.-E. cereals, the figure rises to 60%.

Data from the study were obtained from NHANES, collected by the National Center for Human Statistics at the C.D.C. via household interviews and physical examinations.

The study found that among the 60% of adults who did not consume supplements containing folic acid, 0% exceeded the upper limit for folic acid intake.

Also affirmed in the study was the value of fortification.

"Our results, in agreement with previous studies, indicate that the consumption of R.-T.-E and/or supplements contributes significantly to intake of folic acid and that supplements or R.-T.-E. are associated with higher serum folate and/or lower homocysteine concentrations."

While noting that the masking of vitamin B-12 deficiency is a concern among older adults, Dr. Yang noted that the "vast majority" of adults exceeding the upper intake level for folic acid also are consuming vitamin B-12 in supplements.

In any event, Dr. Rosenberg said the 2.7% of the population with intake above the U.L. should not lead to criticism of fortification.

"Any putative overexposure in the U.S. population should be attributed to supplement use and not to F.D.A.’s historically successful program of flour fortification to prevent a substantial number of neural tube defect births," Dr. Rosenberg said.

The second study’s scope extended beyond grain-based foods and supplements.

"Total folate and folic acid intake from foods and dietary supplements in the United States: 2003-2006," was written by a team led by Regan L. Bailey. Dr. Bailey is a post-doctoral research fellow at the Office of Dietary Supplements, National Institutes of Health, Bethesda.

Dr. Bailey’s study found that "improved total folate intake is warranted in targeted subgroups, which include women of childbearing age and non-Hispanic black women, whereas other population groups are at risk of excessive intake."

In the study, the use of dietary supplements was reported by 53% of NHANES participants with 35% taking supplements that contain folic acid. For non-Hispanic blacks, intake of folic acid dietary supplements was 19%, and for Mexican Americans, 18%.

The researchers found the prevalence of excessive intake from food alone was less than 1% for women and less than 2% for men.

"In this study, ’22% of reproductive-age women did not meet the EAR (estimated average requirement) through diet alone," Dr. Bailey said. "When dietary supplements and foods were examined (i.e., total folate intake), 19% of 14–18-y-olds, 17% of 19–30-y-olds, and 15% of 31–50-y-olds did not meet the EAR recommendations. Non-Hispanic black women also had a high prevalence of inadequate intakes, with 29% who did not meet the EAR through diet alone and 23% who did not meet the EAR for total intakes. However, the NHANES data indicate that, whereas some groups have inadequate intakes, other groups are at risk of excessive intakes. It is important to note that when examined separately, 4% of dietary supplement users exceeded the U.L. simply from the use of the supplements alone."

While the studies "represent facets of a demonstration of a remarkable policy success story," Dr. Rosenberg said additional questions about folic acid need to be addressed.

Among these issues is the question of whether the U.L. for folic acid should be set only based on "concern for the folic acid/vitamin B12 interaction."

"Although these two excellent articles strengthen our support for the processes and surveys that permit such analyses, we need to seek mechanisms for updating our public health targets in folate nutrition," Dr. Rosenberg said.