The upper tolerable limit of folic acid is 1000 mcg per day however, this level was determined to avoid masking a vitamin B12 deficiency and not based on folic acid bioavailability and metabolism. In preconception and pregnancy, women are encouraged to take folic acid-based supplements over and above food intake. Increasing the level however to 400 microg on the other hand is likely to lead to unmetabolised folic acid appearance. It also seems that daily consumption of the higher level of 200 microg or less is unlikely to be problematic. Our findings suggest that persons exposed to the current US fortification programme supplying an average of 100 microg per day or less are unlikely to have unmetabolised folic acid in serum. Folic acid was not detected in either the 200 microg or 100 microg (current US regime) doses tested but was present at the highest level (400 microg) tested. Unmetabolised folic acid was detected after the 14-week supplementation period. Serum samples for total folate and folic acid were collected at baseline, after 14-weeks of supplementation, and pre and post (at 1, 2, 3 and 4 hours) each dose tested. The dose was administered in two-equal sized slices consumed at 09.00 hrs and 13.00 hrs. The aim of this study was to capture the short-term effect of folic acid fortification on unmetabolised folic acid in serum after chronic consumption of folic acid.Īfter pre-saturation with 400 microg folic acid supplements daily for 14-weeks, healthy folate replete adults (n = 20) consumed folic acid fortified bread, at three different levels (400 microg, 200 microg, 100 microg) over a period of one week each. The UK and the Republic of Ireland will likely introduce mandatory fortification also in the next year or so. Based on previous research these higher levels are likely to lead to the appearance of unmetabolised vitamin in the circulation, which may have safety implications for sub-groups of the population. ![]() Some researchers have advocated that this be increased to double and even four times this amount. All flour in the USA is fortified with folic acid at a level of 140 microg/100 g which is estimated to supply an extra 100 microg daily to the average diet.
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