Folic acid fortification and public health: Report on threshold doses above which unmetabolised folic acid appear in serum

Abstract
All flour in the USA is fortified with folic acid at a level of 140 μg/100 g which is estimated to supply an extra 100 μg daily to the average diet. Some researchers have advocated that this be increased to double and even four times this amount. 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. The UK and the Republic of Ireland will likely introduce mandatory fortification also in the next year or so.