The Folic Acid and Creatine Trial: Treatment Effects of Supplementation on Arsenic Methylation Indices and Metabolite Concentrations in Blood in a Bangladeshi Population

BACKGROUND: Chronic arsenic (As) exposure is a global environmental health issue. Inorganic As (InAs) undergoes methylation to monomethyl (MMAs) and dimethyl-arsenical species (DMAs); full methylation to DMAs facilitates urinary excretion and is associated with reduced risk for As-related health outcomes. Nutritional factors, including folate and creatine, influence one-carbon metabolism, the biochemical pathway that provides methyl groups for As methylation. OBJECTIVE: Our aim was to investigate the effects of supplementation with folic acid (FA), creatine, or the two combined on the concentrations of As metabolites and the primary methylation index (PMI: MMAs/InAs) and secondary methylation index (SMI: DMAs/MMAs) in blood in Bangladeshi adults having a wide range of folate status. METHODS: In a randomized, double-blinded, placebo (PBO)-controlled trial, 622 participants were recruited independent of folate status and assigned to one of five treatment arms: a) PBO ([Formula: see text]), b) [Formula: see text] FA/d (400FA; [Formula: see text]), c) [Formula: see text] FA/d (800FA; [Formula: see text]), d) [Formula: see text] creatine/d (creatine; [Formula: see text]), or e) [Formula: see text] ([Formula: see text]; [Formula: see text]) for 12 wk. For the following 12 wk, half of the FA participants were randomly switched to the PBO while the other half continued FA supplementation. All participants received As-removal water filters at baseline. Blood As (bAs) metabolites were measured at weeks 0, 1, 12, and 24. RESULTS: At baseline, 80.3% ([Formula: see text]) of participants were folate sufficient ([Formula: see text] in plasma). In all groups, bAs metabolite concentrations decreased, likely due to filter use; for example, in the PBO group, blood concentrations of MMAs (bMMAs) ([Formula: see text]) decreased from [Formula: see text] at baseline to [Formula: see text] at week 1. After 1 wk, the mean within-person increase in SMI for the [Formula: see text] group was greater than that of the PBO group ([Formula: see text]). The mean percentage decrease in bMMAs between baseline and week 12 was greater for all treatment groups compared with the PBO group [400FA: [Formula: see text] (95% CI: [Formula: see text] , [Formula: see text]), 800FA: [Formula: see text] (95% CI: [Formula: see text] , [Formula: see text]), creatine: [Formula: see text] (95% CI: [Formula: see text] , [Formula: see text]), [Formula: see text]: [Formula: see text] (95% CI: [Formula: see text] , [Formula: see text]), PBO: [Formula: see text] (95% CI: [Formula: see text] , 0.04)], and the percentage increase in blood DMAs (bDMAs) concentrations for the FA-treated groups significantly exceeded that of PBO [400FA: 12.8 (95% CI: 10.5, 15.2), 800FA: 11.3 (95% CI: 8.95, 13.8), [Formula: see text]: 7.45 (95% CI: 5.23, 9.71), PBO: [Formula: see text] (95% CI: [Formula: see text] , 2.63)]. The mean decrease in PMI and increase in SMI in all FA groups significantly exceeded PBO ([Formula: see text]). Data from week 24 showed evidence of a reversal of treatment effects on As metabolites from week 12 in those who switched from 800FA to PBO, with significant decreases in SMI [[Formula: see text] (95% CI: [Formula: see text] , [Formula: see text])] and bDMAs [[Formula: see text] (95% CI: [Formula: see text] , [Formula: see text])], whereas PMI and bMMAs concentrations continued to decline [[Formula: see text] (95% CI: [Formula: see text] , [Formula: see text]) and [Formula: see text] (95% CI: [Formula: see text] , [Formula: see text]), respectively] for those who remained on 800FA supplementation. CONCLUSIONS: FA supplementation lowered bMMAs and increased bDMAs in a sample of primarily folate-replete adults, whereas creatine supplementation lowered bMMAs. Evidence of the reversal of treatment effects on As metabolites following FA cessation suggests short-term benefits of supplementation and underscores the importance of long-term interventions, such as FA fortification. https://doi.org/10.1289/EHP11270