Folic acid - Fortification - 2
Folic acid fortification with pteroylmonoglutamic acid (PGA) is not the natural form of the folic acid but is cheap and stable. 5-methyl-H4 folate (5-MTHF) is the major transport form of the vitamin outside the cell. A single dose of 400 mcg (or less) of PGA is converted efficiently into 5-methyl-H4 folate during absorption. The absorption and biotransformation process is saturated at this 400 mcg dose, and anything higher intake will lead to unmodified PGA appearing in the blood which have unknown toxicity.
[BMJ USA, March 2004;4:127-131. 41556