Joint effects of urinary arsenic methylation capacity with potential modifiers on arsenicosis: A cross-sectional study from an endemic arsenism area in Huhhot Basin, northern China

A lower arsenic methylation capacity is believed to be associated with various arsenic-related diseases. However, the synergistic effect of the arsenic methylation capacity and potential modifiers on arsenicosis risk is unclear. The current study evaluated the joint effect of the arsenic methylation capacity with several risk factors on the risk of arsenicosis characterized by skin lesions. In total, 302 adults (79 arsenicosis and 223 non-arsenicosis) residing in an endemic arsenism area in Huhhot Basin were included. Urinary levels of inorganic arsenic (iAs), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) were determined, and the percentages of arsenic species (iAs%, MMA%, and DMA%), as well as two methylation indices (primary methylation index, PMI, and secondary methylation index, SMI), were calculated to assess the arsenic methylation capacity of individuals. The results showed that a lower methylation capacity, which is indicated by higher MMA% values and lower DMA% and SMI values, was significantly associated with arsenicosis after the adjustment for multiple confounders. The relative excess risk for interactions between higher MMA% values and older age was 2.35 (95% CI: −0.56, 5.27), and the relative excess risk for interactions between higher MMA% values and lower BMI was 1.08 (95% CI: −1.20, 3.36). The data also indicated a suggestive synergistic effect of a lower arsenic methylation capacity (lower DMA% and SMI) with older age, lower BMI, and male gender. The findings of the present study suggest that a lower arsenic methylation capacity was associated with arsenicosis and that certain risk factors may enhance the risk of arsenic-induced skin lesions.