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. 2020 Jan;63(1):36-43.
doi: 10.1002/ajim.23060. Epub 2019 Oct 24.

Manganese exposure, parkinsonian signs, and quality of life in South African mine workers

Wendy W Dlamini  1   2 , Gill Nelson  1   3 , Susan Searles Nielsen  2 , Brad A Racette  1   2
Affiliations

Manganese exposure, parkinsonian signs, and quality of life in South African mine workers

Wendy W Dlamini et al. Am J Ind Med. 2020 Jan.

Abstract

Background: Manganese (Mn) neurotoxicity is associated with parkinsonism; the associated motor deficits can affect individuals' quality of life (QoL). We investigated associations between Mn exposure, parkinsonian signs, and QoL in Mn mine workers.

Methods: We assessed parkinsonian signs and QoL in 187 black South African Mn mine workers, using the Unified Parkinson Disease Rating Scale motor subsection 3 (UPDRS3) and the Parkinson Disease Questionnaire (PDQ-39), respectively. We estimated cumulative Mn exposure in mg Mn/m3 -years using complete occupational histories and a job-exposure matrix. We investigated the cross-sectional association between cumulative Mn exposure and UPDRS3 score, and the UPDRS3 score and PDQ-39, adjusting for age, using linear regression.

Results: Participants' mean age was 41.8 years (range, 21-67 years); 97.3% were male. Estimated mean cumulative Mn exposure at the time of examination was 5.4 mg Mn/m3 -years, with a mean of 14.0 years working in a Mn mine. The mean UPDRS3 score was 10.1 and 25.7% of the workers had a UPDRS3 score greater than or equal to 15. There was a U-shaped dose-response relation between cumulative Mn exposure and UPDRS3 score, with a positive association up to 15 mg Mn/m3 -years of exposure and an inverse association thereafter. Greater UPDRS3 scores were associated with poorer self-reported QoL.

Conclusion: In this cohort of employed Mn mine workers, parkinsonian signs were common and were associated with both estimated cumulative Mn exposure and poorer QoL.

Keywords: manganese; miners; parkinsonian disorders.

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Conflict of interest statement

Disclosure (Authors): The authors declare no conflicts of interest.

Figures

Figure 1:
Figure 1:. Directed acyclic graph (DAG) for manganese, parkinsonism, quality of life, and potential confounders
The DAG illustrates the hypothesised causal relationships between manganese exposure, parkinsonism, and QoL, and the associations between potential confounders (age, smoking, and alcohol) and both manganese exposure and parkinsonism. (Note: Age is also a potential confounder in the association between parkinsonism and QoL.) Abbreviations: UPDRS3 = Unified Parkinson’s Disease Rating Scale motor subsection part 3; PDQ-39 = Parkinson’s Disease Questionnaire-39.
Figure 2:
Figure 2:. Participating South African Mn mine workers (N = 187)
We included all Mn mine workers who had a complete UPDRS3 score (examination), who were not missing Mn exposure data (work history data as of the date of the UPDRS3 exam), and who were not missing the PDQ-39 questionnaire data. Abbreviations: Mn = manganese; UPDRS3 = Unified Parkinson’s Disease Rating Scale motor subsection part 3; PDQ-39 = Parkinson’s Disease Questionnaire-39.
Figure 3:
Figure 3:. Association between cumulative Mn exposure (mg Mn/m3-years) and UPDRS3 score (N = 187)
LOWESS demonstrated a U-shaped association between cumulative Mn exposure (mg Mn/m3-years) and the UPDRS3 score, with a positive association in approximately the lowest 15 mg Mn/m3-years of exposure and an inverse association when cumulative Mn exposure was > 15 mg Mn/m3-years of exposure. Abbreviations: LOWESS = Locally weighted scatterplot smoothing graph; UPDRS3 = Unified Parkinson’s Disease Rating Scale motor subsection 3.
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