Amyotrophic lateral sclerosis after long-term exposure to drinking water with high selenium content

We examined 9 years' incidence of amyotrophic lateral sclerosis, a disease previously associated with a high-selenium environment, in a cohort of 5,182 residents of Reggio Emilia, Italy. This cohort had accidentally been exposed to drinking water with high selenium content. Four cases were diagnosed during the follow up. Using the remainder of the municipal population as the reference group, the standardized incidence ratio was 4.22 (95% confidence interval=1.15-10.80). The standardized incidence ratio was higher after limiting the analysis to the subcohort with the longest ascertainable exposure period. The findings appear to confirm a causal association between overexposure to environmental selenium and amyotrophic lateral sclerosis.