Occupational exposure and brain diseases

Progressive brain diseases such as Parkinson's disease, amyotrophic lateral sclerosis (ALS) and Alzheimer's disease are regularly associated with exposure to environmental factors. They are disorders that mainly occur in older people and despite much research it is not entirely clear how they occur.

Parkinson's, ALS and Alzheimer's

Possible mechanism

In all three brain diseases mentioned, large molecules - usually proteins - play a role that ensure that the brain and nerve cells function normally. These molecules are made over and over again and different enzyme systems influence their production and breakdown. One of the essential features for their functioning is the way they are folded. With age, the number of molecules that are improperly folded or damaged also increases. These “wrong” molecules are stored as waste in cells between the neurons. Over time this disrupts the normal functioning of the nerve cells.

Damage to the protein molecules is promoted by hereditary factors and by exposure to chemical substances. In addition, stress and the influence of metabolism can also play a role. Various systematic literature reviews and meta-analyzes have appeared on a link between occupational exposure and neurodegenerative diseases. The most studied exposures are pesticides, metals and exposure to low-frequency electromagnetic fields (LF-EMF).

Qualitatively good studies on a services

Swedish researchers have now reviewed these systematic reviews and meta-analysis, including only qualitatively good studies in the end result. In this way they want to avoid the influence of publication bias. They conducted the research in accordance with the Meta-analysis of Observational Studies in Epidemiology (MOOSE) and the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) guidelines.

Good quality 66 studies have been included in the meta-analysis that were all aimed at exposure to pesticides, metals or LF-EMF with the resultant of the three brain diseases mentioned: Parkinson's disease, ALS or Alzheimer's disease.

Results

On the basis of 19 studies is the weighted relative risk for exposure to LF-EMF determined. This yielded the following outcomes for the three diseases:

  • ALS; RR = 1,26 (95% confidence interval (BI) 1,07 – 1,50)
  • Alzheimer's disease; RR = 1,33 (95% BI 1,07 – 1,64)
  • Parkinson's disease; RR = 1,02 (95% BI 0,83 – 1,26)

On the basis of 31 studies is the weighted relative risk for exposure to pesticides determined. This yielded the following outcomes for the three diseases:

  • ALS; RR = 1,35 (95% BI 1,02 – 1,79)
  • Alsheimer's disease; RR = 1,50 (95% BI 0,98 – 2,29)
  • Parkinson's disease; RR = 1,66 (95% BI 1,42 – 1,94)

On the basis of 14 studies is the weighted relative risk for exposure to metal, of which only the five studies on exposure to lead showed an increased risk for ALS and Parkinson's disease: RR = 1,57 (95% BI 1,11 – 2,20). The weighted RR for non-lead exposure to metals was 0,97 (95% BI 0,88 – 1,06).

Conclusion

The researchers then conclude that exposure to pesticides increases the risk of getting a neurodegenerative disorder by at least 50%. Exposure to lead has only been investigated for ALS and Parkinson's disease and here too there appears to be an increase in risk with 50%. Occupational exposure to LF-EMF appears to increase the risk of ALS and Alzheimer's disease by around 10%.

Source: Lars-Gunnar Gunnarsson and Lennart Bodin Occupational Exposures and Neurodegenerative Diseases — A Systematic Literature Review and Meta-Analyzes Int. J. Environ. Res. Public Health 2019, 16, 337; doi: 10.3390 / ijerph16030337

Read also Pesticides and Parkinson's disease

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