Chapter 20: Epidemiological Studies of Parkinsonism in Welders

Welders have been the focus of numerous epidemiological studies addressing possible etiologic relations between manganese (Mn) and Parkinson disease (PD). These include investigations of defined cohorts of welders, which we regard as most informative, general population surveys of welding occupations, and population-based case-control studies. With a few notable exceptions among the studies of defined cohorts of welders, there is little evidence that welders are at increased risk of PD. However, most prior research has suffered from severe limitations due to incomplete ascertainment of incident cases, questionable diagnostic accuracy, and non-specific Mn exposure assessment that precludes quantitative dose–response estimation. A potential etiologic relation between environmental Mn exposure and PD continues to be an important scientific and public health topic, given the ubiquitous nature of Mn exposure. Investigations of welders, who experience some of the highest Mn doses in the population, should remain a priority. Recommended future epidemiological research should involve longitudinal assessments of risk, severity, and progression of clinically diagnosed PD among well-characterized cohorts of welders, whose exposures to Mn and potential confounders can be assessed quantitatively.