Table 2.

Geometric mean ratio (95% CI) of HOMA2–IR at baseline and follow-up by inorganic arsenic exposure and arsenic metabolism biomarkers.

Arsenic exposure/biomarker	Biomarker	Baseline effect	Annual change	5-y follow-up
Arsenic exposure ($n=\mathrm{1,838}$)
$\mathrm{\Sigma }\mathrm{As}$, $\mathrm{\mu }\mathrm{g}/\mathrm{g}$ (6.9 vs. 2.9)		1.04 (1.01, 1.08)	0.98 (0.97, 0.99)	0.95 (0.92, 0.98)
Arsenic metabolism ($n=\mathrm{1,774}$)
Conventional approach	iAs%	0.99 (0.97, 1.01)	1.00 (0.99, 1.00)	0.97 (0.95, 0.99)
(5% increase)	MMA%	0.91 (0.88, 0.93)	1.00 (1.00, 1.01)	0.93 (0.91, 0.95)
	DMA%	1.04 (1.02, 1.05)	1.00 (1.00, 1.00)	1.04 (1.02, 1.05)
Leave-one-out approach
iAs% (5% increase)	MMA% (5% decrease)	1.10 (1.06, 1.14)	1.00 (0.99, 1.00)	1.08 (1.04, 1.12)
	DMA% (5% decrease)	1.01 (0.98, 1.03)	1.00 (0.99, 1.00)	0.99 (0.97, 1.01)
MMA% (5% increase)	iAs% (5% decrease)	0.91 (0.88, 0.94)	1.00 (1.00, 1.01)	0.93 (0.90, 0.96)
	DMA% (5% decrease)	0.91 (0.88, 0.93)	1.00 (1.00, 1.01)	0.93 (0.91, 0.95)
DMA% (5% increase)	iAs% (5% decrease)	1.00 (0.98, 1.02)	1.00 (1.00, 1.00)	1.00 (0.98, 1.02)
	MMA% (5% decrease)	1.09 (1.06, 1.12)	1.00 (1.00, 1.00)	1.09 (1.06, 1.12)

Note: In arsenic exposure analysis, the geometric mean ratio (95% CI) are reported per an increase equal to the IQR in $\mathrm{\Sigma }\mathrm{As}$ distribution. Arsenic metabolism analyses were conducted in two ways. In the conventional approach, each arsenic metabolism biomarker is entered alone in the model and the geometric mean ratios (95% CI) are reported per a 5% increase in that specific biomarker. In the leave-one-out approach, two arsenic metabolism biomarkers are entered together in the model. In that model, a 5% increase in one of the modeled biomarkers corresponds to a 5% decrease of the biomarker that is left outside the model. Models were stratified by study region and adjusted for sex, age at baseline, baseline education ($<12\mathrm{y}$, $\ge 12\mathrm{y}$), body mass index (${\mathrm{kg}/\mathrm{m}}^2$), waist circumference, smoking status (never, former, current smoker), estimated glomerular filtration rate ($\mathrm{mL}/\text{min}\text{per}1.73{\mathrm{m}}^2$), fasting glucose status at baseline (normal, impaired), estimated dietary vitamin B2, vitamin B6, and folate and AS3MT genotype. All arsenic metabolism models were also adjusted for log-transformed $\mathrm{\Sigma }\mathrm{As}$ concentrations ($\mathrm{\mu }\mathrm{g}/\mathrm{g}$). CI, confidence interval; DMA%, proportion of dimethylarsinate; HOMA2-IR, homeostasis model assessment for insulin resistance; iAs%, proportion of inorganic arsenic; IQR, interquartile range; MMA%, proportion of monomethylarsonate; $\mathrm{\Sigma }\mathrm{As}$, sum of iAs, MMA, and DMA urine concentrations.