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Employment as a Welder and Parkinson Disease Among Heavy Equipment Manufacturing Workers

Marsh, Gary M. PhD; Gula, Mary Jean MS

Journal of Occupational and Environmental Medicine: October 2006 - Volume 48 - Issue 10 - p 1031-1046
doi: 10.1097/01.jom.0000232547.74802.d8
Original Articles

Objective: We investigated whether employment as a welder with potential exposure to manganese and other substances is associated with Parkinson disease (PD), parkinsonism or related neurological disorders, or accelerates the age of onset of PD.

Methods: We selected cases and controls from 12,595 persons ever employed at three Caterpillar Inc. (CAT) plants between 1976 and 2004 with potential to make a medical insurance claim between 1998 and 2004. Cases had filed a claim for 1) PD, 2) “secondary parkinsonism”, 3) “other degenerative diseases of the basal ganglia” or 4) “essential and other specific forms of tremor”. Cases were grouped by claims: Group 1-claims 1 and 2 and Group 2-claims 1 to 4, and as study period incident (SPI) or prevalent. Each case was matched to two series of 10 controls each on date of case’s first claim, year of birth, race and sex. Series I was also matched on plant.

Results: Odds ratios (OR) and 95% confidence intervals (CI) for the variable, “ever welder in any CAT plant” were: Group 1-SPI Cases: Series I (OR = .76, CI = .26–2.19), Series II (OR = .81, CI = .29–2.25); Group 1- Prevalent Cases: Series I (OR = .82, CI = .36–1.86), Series II (OR = .97, CI = .42–2.23); Group 2- SPI Cases: Series I (OR = 1.03, CI = .57–1.87), Series II (OR = 1.21, CI = .67–2.20) Group 2-Prevalent Cases: Series I (OR = 1.02, CI = .62–1.71), Series II (OR = .86, CI = .51–1.43). Our finding of no statistically significant associations for welding employment was maintained following adjustment for potential confounding and evaluation of possible effect modification. Employment as a welder did not accelerate the age of onset of PD.

Conclusions: Our study supported the conclusion that employment as a welder is not associated with Parkinson disease, parkinsonism or a related neurological disorder.

From the Department of Biostatistics (Dr Marsh), Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania; and a consultant, Verona, Pennsylvania (formerly, Department of Biostatistics, University of Pittsburgh) (Ms Gula).

This research was funded through Caterpillar Inc. Gary Marsh performed this work as a consultant to Caterpillar, Inc. The research protocol was approved by the Institutional Review Board (IRB) of the University of Pittsburgh, which considers this consulting work a usual professional activity. There are pending legal cases against Caterpillar, and Dr. Marsh may be asked to serve as an expert witness given his role as director of this research project.

Address correspondence to: Gary M. Marsh, PhD, Department of Biostatistics Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261; E-mail:

©2006The American College of Occupational and Environmental Medicine