Arsenic Methylation and Body Composition among Pregnant Women in Rural Northern Bangladesh: The Pregnancy, Arsenic, and Immune Response (PAIR) Study

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BACKGROUND AND AIM: Arsenic methylation—the conversion of inorganic arsenic (iAs) to less toxic monomethyl (MMA) and dimethyl (DMA) species—could modify the developmental and reproductive toxicity of this metalloid. However, variability in arsenic methylation among pregnant women remains poorly understood. Arsenic methylation efficiency—the percentage of urinary arsenic methylated to DMA (DMA%)—is positively associated with body mass index (BMI) in pregnant women, but BMI is an ambiguous measure of body composition. We estimated arsenic methylation by body fat percentage as well as BMI in pregnant women in Bangladesh. METHODS: We collected spot urine samples from pregnant women (n=784) in gestational weeks 11-17 and measured weight, height, and subscapular and triceps skinfolds. Urinary arsenic was speciated by HPLC-ICPMS. Arsenic metabolism was assessed by urinary iAs, MMA, and DMA, which were specific gravity-corrected, divided by their sum (∑As), and multiplied by 100 (iAs%, MMA%, and DMA%). Body fat (%) was estimated using Siri’s equation with body density estimated from skinfolds. We fit linear models of iAs%, MMA%, or DMA% by body fat or BMI (kg/m2), adjusting for ln ∑As (µg/L), age (years), and gestational week. RESULTS:In complete cases (n=771), median (IQR) iAs%, MMA%, DMA%, and ∑As were 12.1% (5.8%), 6.6% (3.0%), 81.0% (7.5%), and 33.3 µg/L (37.2 µg/L). Median (IQR) body fat and BMI were 28.4% (9.1%) and 21 kg/m2 (4.4 kg/m2), and were highly correlated (Spearman’s rho=0.83). Before adjustment, body fat was negatively associated with iAs% (beta per IQR-unit increase: -1.00, 95%CI: -1.50,-0.50) and MMA% (-0.65, 95%CI: -0.90,-0.39) and positively associated with DMA% (1.65, 95%CI: 1.00,2.30). BMI was negatively associated with iAs% (beta per IQR-unit increase: -0.85, 95%CI: -1.29,-0.41) and MMA% (-0.69, 95%CI: -0.91,-0.47) and positively associated with DMA% (1.54, 95%CI: 0.98,2.10). After adjustment, results were similar. CONCLUSIONS:Arsenic methylation efficiency was positively associated with body fat and BMI among pregnant women in Bangladesh. KEYWORDS: Biomarkers of exposure, Chemical exposures, Female, Heavy metals, Obesity and metabolic disorders, Pregnancy outcomes

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