Associations between urinary arsenic and vitamin D deficiency: a cross-sectional analysis of NHANES 2011-2018.

Arsenic exposure and vitamin D deficiency independently contribute to adverse neurological and systemic outcomes, yet their interplay in the general population has not been thoroughly characterized. We investigated the association between urinary arsenic (total arsenic and dimethylarsinate [DMA]) and vitamin D deficiency and explored how this relationship varies by demographic, behavioral, laboratory, dietary, and neurological comorbidity factors. Using data from 6,148 U.S. adults aged ≥ 18 years in NHANES 2011-2018, we estimated odds ratios (ORs) for deficiency per interquartile‑range increase in each arsenic measure using survey-weighted logistic regression. After full adjustment for demographics, lifestyle, dietary, and clinical factors, the ORs for total urinary arsenic and DMA were 1.30 (95% CI 1.16, 1.45) and 1.50 (95% CI 1.27, 1.78), respectively. Associations were strongest among women; adults aged < 60 years; Non‑Hispanic, highly educated, underweight individuals; as well as current smokers and drinkers. In contrast, participants with stroke or sleep disorders exhibited inverse associations, likely due to routine clinical vitamin D supplementation. These findings demonstrate a robust, dose‑dependent association between arsenic exposure and vitamin D deficiency in U.S. adults. They suggest the importance of integrated public health strategies-combining arsenic mitigation with targeted vitamin D strategies-and highlight the need for longitudinal and interventional studies to establish causality and to determine whether optimizing vitamin D status might potentially modify the adverse health effects of arsenic.