Besides aerotoxicity and chronic traumatic encephalopathy (CTE), as emerging employers’ liability (EL) risks in the aviation and professional sport sectors, neurodegeneration, as a wide-spanning occupational health risk, has been the subject of multiple articles in BC Disease News.
For example, in edition 180 (here), we analysed the results of a Dutch study, which associated amyotrophic lateral sclerosis (ALS), a rare brain disorder, with exposure to extremely low frequency electromagnetic radiation (ELF-MF):
‘Men who were occupationally exposed to high levels of ELF-MFs were 2.19 times more likely to develop ALS than those who had never been exposed to them’.
Elsewhere, in edition 205 (here), we revealed exposure to paraquat, a commonly used herbicide in the UK from 1960 to 2007, was capable of causing Parkinson’s disease in humans with a specific genetic predisposition.
Until recently, however, there has been limited (both in quality and in volume) appreciation of the potentially far-reaching impact of work-related neurodegenerative disease on global workforces.
Filling this void, Gunarsson et al (2019) recently published a comprehensive meta-analysis on occupational exposure to electromagnetic fields (EMFs), metals and pesticides and the effect(s) on relative risk of developing ALS, Parkinson's disease and Alzheimer's disease.[i]
This study was based on 66 separate publications of ‘good scientific epidemiological standard’, unlike preceding meta-analyses.
Examination of 19 publications on exposure to EMF were indicative of a 26% increase in risk of ALS, a 33% increase in risk of Alzheimer's disease and a 2% increase in risk of Parkinson's disease.
Further, reflecting on 31 publications concerned occupational pesticide exposure, it was calculated that there was a 35% increase in risk of ALS, a 50% increase in Alzheimer's disease and a 66% increase in Parkinson's disease.
In addition, after having inspected 14 publications on metal exposure, the researchers concluded that neither welding, nor exposure to a mixture of metals, were involved with neurodegenerative progression.
The same could not be said for exposure to lead-only, however, which carried a 57% increase in risk of ALS or Parkinson’s disease.
On the back of this finding, exploration into a promising link between occupational lead exposure and Alzheimer’s disease may be advisable, as there is currently no epidemiological data to support or oppose an assumption of risk.
The study authors summarised their most significant observations, as follows:
‘Exposure to pesticides increased the risk of getting the mentioned neurodegenerative diseases by at least 50%. Exposure to lead was only studied for ALS and Parkinson's disease and involved 50% increased risk. Occupational exposure to EMFs seemed to involve some 10% increase in risk for ALS and Alzheimer's disease only’.
In respect of study limitations, the researchers accepted that the lack of uniformity between separate publications (e.g. ‘In some studies exposure is graded Yes or No, in others the dosage is graded into 3–4 levels’) could encumber validity, but this risk is almost unavoidable when conducting meta-analyses.
[i] Gunnarsson LG et al., Occupational Exposures and Neurodegenerative Diseases-A Systematic Literature Review and Meta-Analyses. Int J Environ Res Public Health. 2019 Jan 26;16(3). <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6388365/pdf/ijerph-16-00337.pdf> accessed 9 October 2019.