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Background: Selenium is an essential element, but its metabolism in humans is not well characterized. A few small studies indicate that the trimethylselenonium ion (TMSe) is a common selenium metabolite in humans.Objective: This study aimed to elucidate the human metabolism of selenium to TMSe. Design: Study individuals constituted subsamples of 2 cohorts: 1) pregnant women (n = 228) and their 5-y-old children (n = 205) in rural Bangladesh with poor selenium status [median urinary selenium (U-Se): 6.4 mg/L in mothers, 14 mg/L in children] and 2) women in the Argentinian Andes (n = 83) with adequate selenium status (median U-Se: 24 mg/L). Total U-Se and blood selenium were measured by inductively coupled plasma mass spectrometry (ICPMS), and urinary concentrations of TMSe were measured by high-performance liquid chromatography/vapor generation/ICPMS. A genomewide association study (GWAS) was performed for 1,629,299 (after filtration) single nucleotide polymorphisms (SNPs) in the Bangladeshi women (n = 72) by using Illumina Omni5M, and results were validated by using real-time polymerase chain reaction. Results: TMSe "producers" were prevalent (approximately onethird) among the Bangladeshi women and their children, in whom TMSe constituted w10-70% of U-Se, whereas "nonproducers" had, on average, 0.59% TMSe. The TMSe-producing women had, on average, 2-mg U-Se/L higher concentrations than did the nonproducers. In contrast, only 3 of the 83 Andean women were TMSe producers (6-15% TMSe in the urine); the average percentage among the nonproducers was 0.35%. Comparison of the percentage of urinary TMSe in mothers and children indicated a strong genetic influence. The GWAS identified 3 SNPs in the indolethylamine Nmethyltransferase gene (INMT) that were strongly associated with percentage of TMSe (P , 0.001, false-discovery rate corrected) in both cohorts. Conclusions: There are remarkable population and individual variations in the formation of TMSe, which could largely be explained by SNPs in INMT. The TMSe-producing women had higher U-Se concentrations than did nonproducers, but further elucidation of the metabolic pathways of selenium is essential for the understanding of its role in human health. The MINIMat trial was registered at isrctn.org as ISRCTN16581394.Am J Clin Nutr 2015;102:1406-15.

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Background:Hair is a commonly used exposure biomarker for metals and other trace elements, but concern has been raised regarding its appropriateness for assessing the internal dose.Objectives:The aim of the present study was to evaluate children’s hair as biomarker of internal dose for toxic (As, Mn, Cd, Pb) and essential elements (Mg, Ca, Fe, Co, Cu, Zn, Se, Mo).Methods:In 207 children (9–10 years of age), originating from a population-based cohort in rural Bangladesh, we measured concentrations of the selected elements in hair (2cm closest to the scalp) using ICP-MS. We compared these with previously measured concentrations in erythrocytes, urine, and water. For a subset of children (n=19), we analyzed four consecutive 2cm pieces of hair.Results:There were strong associations between hair As and the other biomarkers (erythrocytes: rnormalS=0.73, p<0.001; urine: rnormalS=0.66, p<0.001); and water (rnormalS=0.60, p<0.001); and there were significant correlations between Se in hair and erythrocytes (overall rnormalS=0.38, p<0.001), and urine (rnormalS=0.29, p<0.001). Hair Co and Mo showed weak correlations with concentrations in erythrocytes. Hair Mn was not associated with Mn in erythrocytes, urine, or water, and the geometric mean concentration increased almost five times from the 2cm closest to the head to the 7th–8th cm (p<0.001). Also Mg, Ca, Co, Cd, and Pb increased from the scalp outward (>50% higher in 7th–8th cm compared with 1st–2nd cm, p<0.001).Conclusions:Hair was found to be a useful exposure biomarker of absorbed As and Se only. Of all measured elements, hair Mn seemed the least reflective of internal dose. https://doi.org/10.1289/EHP1239

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Despite decreased water arsenic concentrations in rural Bangladesh, the children still have elevated exposure, largely from food. Considering the known risks of severe health effects in children, additional mitigation strategies are needed.

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