The fortification of flour and grain products with at least 20 percent of the RDA of folic acid per serving (between 0.43 and 1.4 mg per pound) was introduced in the US in 1998 as an effort to address the incidence of pregnancies affected by the neural tube defects (NTDs) caused by folic acid deficiency in the mother.
The CDC and the Institute of Medicine recommend that women of childbearing age take 400 micrograms of folic acid each day to reduce the risk of an NTD-affected pregnancy by 50 to 70 percent, and that intake is upped to 600 micrograms during pregnancy and 500 during lactation.
For the survey published in the August issue of the American Journal of Clinical Nutrition (2005; 82:279-80), researchers analyzed data obtained from the 1999-2000 National Health and Nutrition Examination Survey (NHANES).
As part of the survey, blood samples are collected from around 7,300 participants aged 3 years and over, which were then analyzed for certain B vitamin status-indicators - that is, concentrations of serum and red blood cell folate, serum vitamin B12, and plasma total homocysteine and methylmalonic acid in the US population.
Noting that levels appeared to have increased across the board compared to NHANES data collected prior to the introduction of the program, the researchers concluded that "every segment of the US population appears to benefit from folic acid fortification".
But they do not pretend that this is the final word on the matter; rather, they advise that monitoring of B vitamin concentrations in the US population should continue.
In an editorial to accompany the study, Irwin Rosenberg called the fortification program "probably the most important science-driven intervention in nutrition and public health in decades."
According to the CDC, incidence of neural tube defects has decreased since 1998 by 26 percent.
Despite this success, not all countries have a similar policy. Like the rest of Europe, UK has opted not to introduce it despite pressure from scientists, on the grounds that it may impede the diagnosis of other nutrient deficiencies such as B12, which is common in the elderly.
Ireland is seriously considering it at the moment, since the country has one of the highest incidences of NTDs in Europe - 1-1.5 per 1,000 births - and campaigns encouraging women to take supplements seem to be having little effect.
Back in the US, the FDA has claimed that the level of fortification in foods means that daily intake from all sources would remain below 1mg per day, unless consumers elevate their levels through abuse of dietary supplements. This, it says, removes the risk of complicate the diagnosis of other deficiency-related conditions, like pernicious anemia.
But according to Rosenberg, no coherent plan was made when the program was introduced to monitor its effect on neural tube defect births, folate status, or any possible untoward effects in the population.
For any country considering mandatory fortification, he advises that effectiveness and safety should be fully evaluated.
"Although such an evaluation may be costly, the target population of a nationwide or global intervention deserves to be informed about its effectiveness with regard to health promotion, disease prevention, and safety," he wrote.