5-Formyltetrahydrofolate in a Cohort of Pregnant Women Following Folic Acid Supplementation.

Disrupted folate metabolism related to high synthetic folic acid (FA) intake is a matter of contention. FA and its metabolites play a critical role in DNA synthesis and methylation, and inadequate or imbalanced folate status is strongly associated with neural tube defects and other adverse health outcomes. We determined different folate forms using the LC/MS-MS method in maternal blood, cord blood, and breast milk of women (n = 50) following the National Iron-Folic Acid (FA) Supplementation Program. High concentrations of 5-formyltetrahydrofolate (5-formyl-THF) (range: 40.9-222.7 nmol/L) were observed throughout pregnancy, in cord serum, and breast milk. Levels of 5-formyl-THF rapidly increased (mean difference: 181.6 nmol/L) after 4-6 weeks of supplementation with 1 mg of FA/day and subsequently decreased (mean difference: 139.8 nmol/L) upon continuous supplementation at 400 μg of FA/day. The rapid increase in 5-formyl-THF following supplementation was higher (p < 0.001) in women with methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism. 5-methyl-THF (range: 11.4-56.8 nmol/L) and FA (range: 26.8-39.6 nmol/L) were detected only in breast milk. MTHFR 677CT/TT genotypes were associated with lower 5-methyl-THF (p < 0.001) and higher (p < 0.001) 5-formyl-THF in breast milk. At baseline, 48% had low (<340 nmol/L) RBC folate, but the concentrations continuously increased (p < 0.001) across pregnancy despite the different FA doses. The unusual observation of high 5-formyl-THF, the futile folate form, and its modulation with FA dose and genetic polymorphism merit further investigation to elucidate the population dynamics and possible physiological/clinical significance while questioning the utility of RBC folate as a biomarker of usable folate forms.