One-carbon metabolism nutrient intake and the association between body mass index and urinary arsenic metabolites in adults in the Chihuahua cohort.

BACKGROUND: Exposure to inorganic arsenic (iAs) via drinking water is a serious global health threat. Various factors influence susceptibility to iAs-associated health outcomes, including differences in iAs metabolism. Previous studies have shown that obesity is associated with iAs metabolism. It has been hypothesized that this association can be explained by confounding from nutritional factors involved in one-carbon metabolism, such as folate or other B vitamins, whose intake may differ across BMI categories and is known be associated with iAs metabolism. However, no studies have explored whether this association is confounded by nutritional factors.

METHODS: We investigated the relationship between body mass index (BMI) and the distribution of urinary arsenic species in a cross-sectional cohort of 1166 adults living in Chihuahua, Mexico from 2008 to 2013. Nutrient intake related to one-carbon metabolism, including folate, vitamin B2, and vitamin B12, was assessed using a food frequency questionnaire developed for Mexican populations. Multivariable linear regression was used to estimate the association between BMI and the distribution of urinary arsenic metabolites. Effect modification by drinking water iAs level and sex was also examined.

RESULTS: After adjusting for potential confounders, including age, educational attainment, smoking, alcohol consumption, seafood consumption, water iAs, and sex, BMI was negatively associated with the proportion of urinary inorganic arsenic (%U-iAs) and urinary monomethylated arsenic (%U-MMAs) and positively associated with urinary dimethylated arsenic (%U-DMAs). This relationship was not influenced by additional adjustment for folate, vitamin B2, or vitamin B12 intake. Additionally, there was significant effect modification by both drinking water iAs level and sex.

CONCLUSIONS: This study provides further evidence for an association between BMI and arsenic metabolism. However, contrary to previous hypotheses, these results suggest that this association is not confounded by the intake of micronutrients involved in one-carbon metabolism.