The goal of the present study was to compare the arsenic methylation capacities in elementary school and junior high school students in an area of Taiwan with low arsenic exposure, and explore the influence of both arsenic methylation capacity and obesity on insulin resistance in these children and adolescents using the HOMA-IR index. We recruited 303 elementary school students and 319 junior high school students in Taipei City from September 2007 to November 2011. Concentrations of inorganic arsenic (arsenite + arsenate), monomethylarsonic acid (MMAV) and dimethylarsinic acid (DMAV) were determined by a high-performance liquid chromatography-linked hydride generator and atomic absorption spectrometry. Insulin resistance was determined by HOMA-IR. Elementary school students had significantly lower inorganic arsenic percentage and a higher DMAV percentage than junior high school students. It seems that the former had better arsenic methylation capability than the latter. The HOMA-IR value was significantly and positively related to the sum of the urinary inorganic and methylated arsenic (TotalAs) concentrations and also the BMI Z score, with the regression coefficients (β) being 0.058 (p <0.001) and 0.001 (p = 0.027), respectively. The higher BMI values and higher TotalAs concentration were associated with higher HOMA-IR values in children and adolescents in Taiwan.
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