In Brazil, most folic acid (FA) containing supplements contain 5 mg FA. This dose is usually prescribed for patients with chronic hemolytic anemia and for women planning pregnancy. The effects of high FA doses on vitamin B1, B2 and B6 status including the kynurenine pathway are still unclear.


To assess the effects of a daily intervention with 5 mg FA in healthy subjects on vitamins B1, B2 and B6 serum marker status and serum concentration ok kynurenines.

Material and Methods

Thirty health subjects participated in a 5 mg/day FA intervention. Blood samples were obtained at baseline (D0) and after 45 (D45) and 90 days (D90) of intervention. We assessed serum concentrations of vitamin B6 (pyridoxal-5'-phosphate (PLP), pyridoxal (PL) and 4-pyridoxic acid (PA)), vitamin B2 (riboflavin and flavin mononucleotide (FMN)) and vitamin B1 vitamers (thiamine and thiamine monophosphate (TMP)), as well as tryptophan, kynurenine and several metabolites of tryptophan catabolism in the kynurenine pathway (3-hydroxykynurenine (HK), kynurenic acid (KA), anthranilic acid (AA), xanthurenic acid (XA), 3-hydroxyanthranilic acid (HAA), picolinic acid (Pic) and quinolinic acid (QA)) using LC-MS/MS. PA ratio (PAr) was calculated by PA/(PLP + PL). All variables were normalized by Box-Cox transformation. Comparisons were performed by repeated-measures ANOVA.


Concentrations of all vitamin B6 vitamers (PLP, PL and PA), as well as PAr, were similar at baseline and D45 and D90 of FA intervention. No differences were found among serum vitamin B2 vitamers (riboflavin and FMN) after FA intervention. However, a trend for a decrease in serum TMP concentrations was observed at D90 (P = 0.054). No changes in serum tryptophan and all serum kynurenine pathway metabolites were observed after intervention with FA compared with baseline, except for AA, which was higher at D45 and D90 than baseline (P < 0.001).


Our data suggest that daily use of 5 mg FA by healthy subjects may interfere with vitamin B1 status markers. In addition, serum AA increased with FA intervention, which suggest that the use of high dose FA supplements might affect the kynurenine pathway.

Financing: FAPESP (2016/18854-4) and CNPq (401586/2014-6)


No relevant conflicts of interest to declare.

Author notes


Asterisk with author names denotes non-ASH members.

Sign in via your Institution