Low-level exposure to arsenic in drinking water and incidence rate of stroke: A cohort study in Denmark

Introduction: High arsenic concentration in drinking water is associated with a higher incidence rate of stroke, but only few studies have investigated an association with arsenic in drinking water at low concentration (<50 μg/L). Objective: To examine if arsenic in drinking water at low concentration was associated with higher incidence rate of stroke in Denmark. Methods: A total of 57,053 individuals from the Danish Diet, Cancer, and Health cohort was included in the study (enrolment in 1993–1997, age 50–64 years), of which 2195 individuals had incident stroke between enrolment and November 2009. Individuals were enrolled in two major cities (Copenhagen and Aarhus). Residential addresses in the period 1973–2009 were geocoded and arsenic concentration in drinking water at each address was estimated by linking addresses with water supply areas. Associations between arsenic concentration and incidence rate of stroke were analysed using a generalized linear model with a Poisson distribution. Incidence rate ratios (IRR) were adjusted for differences in age, sex, calendar-year, lifestyle factors, and educational level. Results: Median arsenic concentration in drinking water was 0.7 μg/L at enrolment addresses (range: 0.03 to 25 μg/L), with highest concentrations in the Aarhus area. The adjusted IRRs were 1.17 (95% CI: 1.04–1.32) for the highest arsenic quartile (1.93–25.3 μg/L) when compared with the lowest quartile (0.049–0.57 μg/L), but the highest IRR was seen in the second quartile (0.57–0.76 μg/L) (IRR = 1.21; 95% CI: 1.07–1.36). The highest IRR in the upper quartile was seen in the Aarhus area (IRR = 1.79; 95% CI: 1.41–2.26). Having ever been exposed to10 μg/L or more arsenic in drinking water resulted in an IRR at 1.44 (95% CI: 1.00–2.08) for all strokes and 1.63 (95% CI: 1.11–2.39) for ischemic strokes. Conclusion: The results indicate that arsenic in drinking water even at low concentration is associated with higher incidence rate of stroke.