Occupational exposures and Parkinson's disease mortality in a prospective Dutch cohort
Brouwer M, Koeman T, van den Brandt PA, Kromhout H, Schouten LJ, Peters S, Huss A, Vermeulen R. Occupational exposures and Parkinson's disease mortality in a prospective Dutch cohort. Occup Environ Med. 2015 Feb 23. pii:oemed-2014-102209. doi: 10.1136/oemed-2014-102209. [Epub ahead of print]
OBJECTIVES: We investigated the association between six occupational exposures (ie, pesticides, solvents, metals, diesel motor emissions (DME), extremely low frequency magnetic fields (ELF-MF) and electric shocks) and Parkinson's disease (PD) mortality in a large population-based prospective cohort study.
METHODS: The Netherlands Cohort Study on diet and cancer enrolled 58 279 men and 62 573 women aged 55-69 years in 1986. Participants were followed up for cause-specific mortality over 17.3 years, until December 2003, resulting in 402 male and 207 female PD deaths. Following a case-cohort design, a subcohort of 5 000 participants was randomly sampled from the complete cohort. Information on occupational history and potential confounders was collected at baseline. Job-exposure matrices were applied to assign occupational exposures. Associations with PD mortality were evaluated using Cox regression.
RESULTS: Among men, elevated HRs were observed for exposure to pesticides (eg, ever high exposed, HR 1.27, 95% CI 0.86 to 1.88) and ever high exposed to ELF-MF (HR 1.54, 95% CI 1.00 to 2.36). No association with exposure duration or trend in cumulative exposure was observed for any of the occupational exposures. Results among women were unstable due to small numbers of high-exposed women.
CONCLUSIONS: Associations with PD mortality were observed for occupational exposure to pesticides and ELF-MF. However, the weight given to these findings is limited by the absence of a monotonic trend with either duration or cumulative exposure. No associations were found between PD mortality and occupational exposure to solvents, metals, DME or electric shocks.
What this paper adds
- Different occupational exposures have been associated with an increased risk of Parkinson's disease (PD), but evidence from prospective cohort studies is limited.
- The Netherlands Cohort Study on Diet and Cancer is a large prospective cohort study with complete occupational histories up to baseline and 17.3 years of follow-up, enabling a comprehensive study on the association between different occupational exposures and PD mortality.
- This study found associations between PD mortality and exposure to pesticides and extremely low frequency magnetic fields, but neither association with exposure duration nor a trend in cumulative exposure was observed.
- No association between PD mortality and occupational exposure to solvents, metals, diesel motor emissions or electric shocks was found.
- This study does not support the hypothesis that the investigated occupational exposures increase PD mortality, although we cannot exclude that small risks may exist.
... Other neurodegenerative diseases (ie, AD and amyotrophic lateral sclerosis (ALS)) have been associated primarily with electrical occupations rather than extremely low frequency magnetic field (ELF-MF) exposure and it has been hypothesised that this association may be related to electric shocks rather than to magnetic fields.18 ,19 Few studies have reported on a positive association between occupational exposure to ELF-MF and PD 20 but it is possible that electric shocks are involved as little knowledge exists regarding a potential association between electric shocks and PD....
... ELF-MF exposure was determined with an adapted version of the ELF-MF JEM of Bowman et al.26 ,27 Furthermore, risk of electric shocks at work was assigned with a newly developed shock-JEM based on electrical injury registration data.28 ...
... For men, the percentage of cases ever exposed (ever only low or ever high) varied between 10% (herbicides) and 52% (ELF-MF) (table 2). Women had shorter occupational histories than men (13 vs 36 years on average) and very few women were ever high exposed to any of the occupational exposures, with ever high exposure to pesticides being most prevalent. Owing to the overall low prevalence of (high) exposed women, we only present the results for men here ...
... Ever high exposure to ELF-MF was significantly associated with PD mortality (HR 1.54, 95% CI 1.00 to 2.36), but there was no trend with increasing cumulative exposure (p=0.79). Decreased HRs were observed for the first tertile of aromatic solvent exposure (HR 0.62, 95% CI 0.40 to 0.97), and for risk of electric shocks (ever high, HR 0.79, 95% CI 0.59 to 1.06), of which the latter association was non-significant ...
... When analysing exposure to pesticides, insecticides, aromatic solvents, ELF-MF, electric shocks or DME, pairwise adjusted for the other occupational exposures, the HRs for exposure to pesticides, insecticides and ELF-MF only changed marginally (see online supplementary table S3) ...
... Elevated HRs for PD mortality were observed for exposure to pesticides and ELF-MF, which remained so even after adjusting for the other occupational exposures. However, we found no association with exposure duration and no trend in cumulative exposure for these two exposures. No associations between PD mortality and occupational exposure to solvents, metals, DME or risk of electric shocks were observed....
A significant increased HR was observed for PD mortality among men ever high exposed to ELF-MF. Literature on the association between ELF-MF exposure and PD primarily shows null findings, 20 which is strengthened by the absence of knowledge on possible biological mechanisms involved. Studies focusing on occupations with potentially high ELF-MF exposure did find weak associations with other neurodegenerative diseases, such as AD and ALS, but generally not with PD.19,20 As no effect of cumulative exposure or exposure duration was observed in our study, the weight given to this finding is limited, but we cannot rule out that high exposures to ELF-MF may be related to PD. In this study we did not observe an association between the risk of electric shocks and PD mortality. Little knowledge exists regarding a potential association between electric shocks and PD, but this occupational factor was included because for ALS the suggested association with ELF-MF has been hypothesised to be related to electric shocks, rather than the magnetic fields. 20 When the analysis of ELF-MF exposure was adjusted for risk of electric shocks, the association between ever high exposure to ELF-MF and PD mortality became stronger (HR 1.81, 95% CI 1.15 to 2.85). This suggests that, if the observed association between high exposure to ELF-MF and PD risk is true, this is likely not driven by electric shocks.
In this large prospective population-based cohort study of Dutch men and women, with 17.3 years of follow-up, we found some suggestions for an association between PD mortality and occupational exposure to pesticides and ELF-MF. However, the weight given to these findings is limited by the absence of a monotonic trend with either duration of exposure or cumulative exposure. We found no evidence for associations between PD mortality and occupational exposure to solvents, metals, DME or risk of electric shocks. This study does not support the hypothesis that the investigated occupational exposures increase PD mortality, although we cannot exclude that small risks do exist.
18. Li C, Sung F. Association between occupational exposure to power frequency electromagnetic fields and amyotrophic lateral sclerosis: a review. Am J Ind Med 2003;43:212–20. doi:10.1002/ajim.10148
19. Vergara, Kheifets L,Greenland S, et al. Occupational exposure to extremely low-frequency magnetic fields and neurodegenerative disease: a meta-analysis. J Occup Environ Med 2013;55:135–46. doi:10.1097/JOM.
20. Kheifets L,Bowman JD, Checkoway H, et al. Future needs of occupational epidemiology of extremely low frequency electric and magnetic fields: Review and recommendations. Occup Environ Med 2009;66:72–80. doi:10.1136/oem.2007.037994
Joel M. Moskowitz, Ph.D., Director
Center for Family and Community Health
School of Public Health
University of California, Berkeley
Electromagnetic Radiation Safety
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