This is the synthetic form of folate. It requires conversion before it can be used in the body  [7, 8] and must undergo several metabolic steps (figure 1) to be converted into the active tetrahydrofolate (THF) form and 5-methyltetrahydrofolate (5-MTHF) forms. FA is more stable than natural folates and is cheaper to manufacture which may explain why this form is used in fortification of foods and dietary supplements [9-11]. FA must be first reduced to dihydrofolate (DHF) and then to THF by an enzyme dihydrofolate reducatase (DHFR) [10, 12]. This two-step process to convert FA to THF is slow [13] and easily reaches saturation [14, 15]. This saturation leads to a build-up of FA known as unmetabolized folic acid (UMFA) [16, 17]. UMFA has been found to appear in serum plasma following oral intakes of more than 200mcg of FA. Studies have shown that the amount of FA ingested on a daily basis due to food fortification exceeds original projections [15, 16, 18-21]. The significance of this UMFA is currently unclear, however studies in relation to fertility, pregnancy and breastfeeding suggest it may affect 5-MTHF and folate levels.

Folic acid (FA) has been the traditional form of folate prescribed by Australian practitioners for preconception and pregnancy [4]. Fortification of foods with FA was introduced in Australia to reduce neural tube defects (NTD) and has, by all accounts, been successful [22, 23] . Research, however, has identified that people living in countries with FA fortification of food have an intake that exceeds the original intended dose [9, 15, 24].