Lifetime exposure to arsenic in drinking water and bladder cancer: a population-based case-control study in Michigan, USA

Arsenic in drinking water has been linked with the risk of urinary bladder cancer, but the dose-response relationships for arsenic exposures below 100 mu g/L remain equivocal. We conducted a population-based case-control study in southeastern Michigan, USA, where approximately 230,000 people were exposed to arsenic concentrations between 10 and 100 mu g/L. This study included 411 bladder cancer cases diagnosed between 2000 and 2004, and 566 controls recruited during the same period. Individual lifetime exposure profiles were reconstructed, and residential water source histories, water consumption practices, and water arsenic measurements or modeled estimates were determined at all residences. Arsenic exposure was estimated for 99% of participants' person-years. Overall, an increase in bladder cancer risk was not found for time-weighted average lifetime arsenic exposure > 10 mu g/L when compared with a reference group exposed to < 1 mu g/L (odds ratio (OR) = 1.10; 95% confidence interval (CI): 0.65, 1.86). Among ever-smokers, risks from arsenic exposure > 10 mu g/L were similarly not elevated when compared to the reference group (OR = 0.94; 95% CI: 0.50, 1.78). We did not find persuasive evidence of an association between low-level arsenic exposure and bladder cancer. Selecting the appropriate exposure metric needs to be thoughtfully considered when investigating risk from low-level arsenic exposure.