Paraquat and Parkinson’s Disease: A Systematic Assessment of Recent Epidemiologic Evidence

Abstract

A systematic assessment of recent evidence of the possible relationship between exposure to paraquat and Parkinson’s disease was undertaken. A literature search was performed to identify all recently published relevant papers investigating, reviewing, or commenting upon the potential relationship between exposure to paraquat and Parkinson’s Disease. MEDLINE via PubMed and EMBASE library databases were searched from 2019 to 2024 using search terms “paraquat” and “Parkinson.” PRISMA guidelines for reporting systematic reviews were consulted along with the AMSTAR2 evaluation tool used to assess the quality of reviews. A total of 517 publications were identified in the first search and 923 publications in the broader search. After removal of duplicates, 21 publications were determined to be potentially relevant. Identified cohort studies were published between 2019 and 2021 and represented analyses using data from the Agricultural Health Study (AHS) a study designed and funded by the U.S. National Institutes of Health. These studies revealed no association between paraquat exposure and Parkinson’s disease. With the results of the most recent analyses, there is no compelling scientific argument for claiming causality. These studies examined not only general population groups but especially occupationally exposed populations and found no statistically significant increased risk and no evidence of an exposure-response relationship. In the absence of these key causal considerations, the fact that these studies contribute to the inconsistency of the entire epidemiologic database, nonexistent risk increases and dose-response relationships, a lack of experimental evidence, and the absence of a similar—analogous—example in the practice of causal inference, there is no scientific justification for a causal claim. Organizational conclusions are consistent.