An overwhelming body of evidence links folate deficiency in early pregnancy to increased risk of neural tube defects (NTDs) - most commonly spina bifida and anencephaly - in infants.
This connection led to the 1998 introduction of public health measures in the US and Canada, where all grain products are fortified with folic acid - the synthetic, bioavailable form of folate.
Irwin Rosenberg, a senior scientist based at Tufts University in Boston, said that a report in the January issue of the journal show how the FDA 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.
"This mandate increased folic acid exposure in women of childbearing age without excessive exposure to those beneficiaries and others in the population,” argues Rosenberg.
The article by Dr Yang et al from the Division of Birth Defects and Developmental Disabilities of the Centres of Disease Control and Prevention (CDC), focuses on folic acid intake only, which is used in fortification and supplements from enriched cereal grain products, ready-to-eat cereals, and supplements.
According to Rosenberg, the article demonstrates the value of pre-fortification modelling and illustrates the benefit of such national health and dietary surveys such as National Health and Nutrition Examination Survey (NHANES) from US households on which the FDA models and their validation is based.
The study, using data obtained from NHANES from the period 2003-2006, examined folic acid intake in the US, exploring the percentage of the population with daily intake above the 1,000 micrograms per day, set by the Institutes of Medicine as an upper limit.
The researchers found that only 2.7 per cent of adults consumed more than the daily upper limit for folic acid and at current fortification levels, US 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 upper levels in intake for folic acid.
The study also found that for 42 per cent of Americans, enriched grains are the only major source of folic acid in the diet, and with the addition of ready-to-eat cereals, the figure rises to 60 per cent.
“This argues that any putative overexposure in the US population should be attributed to supplement use and not to the FDA’s historically successful programme of flour fortification to prevent a substantial number of neural tube defect births,” said Rosenberg.