Postprandial serum folic acid response to multiple doses of folic acid in fortified bread

The benefit of the introduction of mandatory folic acid fortification of all flour products in the USA in 1998 has been amply demonstrated in a reduction of neural tube defect births. Doubt has been cast on the actual level of fortification and recent calculations have shown that the level of folic acid fortification is likely to have been over twice the amount mandated. The implication of this is that a greater proportion of the population are likely to have consumed folic acid at >1mg/d, the Food and Drug Administration safe upper level of intake. Using the criteria of appearance of synthetic folic acid in serum, the objective of this pilot study was to investigate the consequences of consumption of baked bread preparations containing 1mg folic acid. Four healthy adult volunteers undertook each dosing schedule 2 weeks apart. This consisted of a single dose of 1000μg, two doses of 500μg, three doses of 333μg, five doses of 200μg and, finally, ten doses of 100μg. Serum was collected pre- and postprandially and analysed for synthetic folic acid by a combined HPLC–microbiological assay for folic acid. Folic acid appeared in all subjects at all test doses, with the effect more pronounced as the standard dose was administered in smaller amounts over the test period. Approaches to optimise folic acid intake in target populations as part of a universal fortification strategy should take into consideration the potential hazard of over-exposure in groups consuming high amounts of flour-based products.