Parkinson's disease and other neurodegenerative disorders among welders: a Danish cohort study

It has been hypothesized that welders are at increased risk for neurological disorders, including Parkinson's disease, but few well-designed cohort studies have been conducted. The risk for Parkinson's disease and other neurodegenerative disorders was examined in an updated follow-up study based on a previous cohort of 5867 Danish welders and 1735 nonwelding metal workers exposed to welding fume. Occupational history and information on smoking were obtained from questionnaires, supplemented by information from the compulsory Danish Supplementary Pension Fund. Hospital contacts, including outpatient data from 1994, for Parkinson's disease and other neurological disorders were ascertained from the Danish National Hospital Register. Based on first-time hospital contacts, standardized hospitalization ratios (SHRs) were calculated for the entire cohort and for welders, metal workers, and nonresponders separately and for the general Danish population in 1987-2008. In an internal analysis of welders, Cox proportional hazard models were used to estimate hospitalization rate ratios (HRRs) for Parkinson's disease associated with lifelong exposure to welding. Overall, 45 cohort members had a hospital contact for Parkinson's disease (SHR, 1.12; 95% confidence interval [CI], 0.82-1.50), of whom 25 were welders (standardized incidence rate ratio, 1.05; 95% CI, 0.68-1.55). When duration of welding was compared among 5736 welders, the HRR was 0.83 (95% CI, 0.59-1.16) per 10 years' welding, after adjustment for smoking. The results of this study do not support the hypothesis that welders are at increased risk for Parkinson's disease; these findings are consistent with those of our previously published analysis. © 2012 Movement Disorder Society.