Arsenic exposure and incidence of type 2 diabetes in Southwestern American Indians

Abstract

Association of urinary arsenic concentration with incident diabetes was examined in American Indians from Arizona who have a high prevalence of type 2 diabetes and were screened for diabetes between 1982 and 2007. The population resides where drinking water contains arsenic at concentrations above federally recommended limits. A total of 150 nondiabetic subjects aged ≥25 years who subsequently developed type 2 diabetes were matched by year of examination and sex to 150 controls who remained nondiabetic for ≥10 years. Total urinary arsenic concentration, adjusted for urinary creatinine level, ranged from 6.6 µg/L to 123.1 µg/L, and inorganic arsenic concentration ranged from 0.1 µg/L to 36.0 µg/L. In logistic regression models adjusted for age, sex, body mass index, and urinary creatinine level, the odds ratios for incident diabetes were 1.11 (95% confidence interval (CI): 0.79, 1.57) and 1.16 (95% CI: 0.89, 1.53) for a 2-fold increase in total arsenic and inorganic arsenic, respectively. Categorical analyses suggested a positive relationship between quartiles of inorganic arsenic and incident diabetes (P = 0.056); post-hoc comparison of quartiles 2-4 with quartile 1 revealed 2-fold higher odds of diabetes in the upper quartiles (OR = 2.14, 95% CI: 1.19, 3.85). Modestly elevated exposure to inorganic arsenic may predict type 2 diabetes in American Indians. Larger studies that include measures of speciated arsenic are required for confirmation.

Keywords: Indians, North American; arsenic; diabetes mellitus, type 2; incidence; nested case-control studies.

Figure 1.

Distributions of total and inorganic urinary arsenic concentrations on a logarithmic scale, adjusted for urinary creatinine concentration and sample date, among southwestern American Indians in Arizona who were screened for diabetes between 1982 and 2007. Black bars, type 2 diabetes cases; white bars, controls.

Figure 2.

Odds ratios for incident type 2 diabetes among southwestern American Indians in Arizona who were screened for diabetes between 1982 and 2007, by quartiles of total arsenic (black bars) and inorganic arsenic (white bars) concentration, relative to the lowest quartile. Results were obtained from logistic regression models that controlled for age, sex, body mass index, and urinary creatinine concentration. Neither relationship was statistically significant, but there was a suggestion of higher incidence of diabetes in persons with higher arsenic concentrations, particularly for inorganic arsenic (P = 0.12 for total arsenic; P = 0.056 for inorganic arsenic). The P values (2-sided) were based on the Wald χ² test.