No Link Found Between Drinking Well Water, Parkinson’s Risk

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by Steve Bryson PhD |

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No significant correlation was found between the consumption of well water and the risk of developing Parkinson’s disease, according to the results of a pooled analysis of multiple studies.

However, there was a high degree of variability — what scientists call heterogeneity — between the selected studies, with some suggesting that the risk of drinking well water may vary in different geographical locations, the investigators noted.

“We found reliance on well water does not appear to increase risk of [Parkinson’s disease] in general, which is contrary to the mainstream notion,” the researchers wrote. “We pointed out the reasons why previous studies have reached different conclusions, hopefully it will remind researchers who are engaged in similar research to heed.”

While no increased risk was found with the consumption of well water in North America, the team did note that “rural residence and pesticide use have been proved in many studies to have a positive correlation with [Parkinson’s disease].”

“We hope to encourage people and public management departments to pay attention to the impact of pesticides and other pollution on land and water sources,” the team wrote.

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The study, “Well-Water Consumption and Risk of Parkinson’s Disease: A Meta-Analysis of 15 Observational Studies,” was published in the journal Neuropsychiatric Disease and Treatment.

Parkinson’s disease is characterized by the loss of neurons that communicate with other nerve cells by releasing the signaling molecule dopamine. The exact mechanism that leads to the death of these cells is not fully understood, but both genetic and environmental factors are thought to play a role. There is a growing body of evidence that Parkinson’s may be influenced by exposure to pesticides and pollution.

The consumption of well water is among such suggested possible environmental disease risk factors and has been extensively studied, due to the potential presence of substances used in industry or run-off of farming pesticides.

However, while some reports suggest well water use increases the risk of Parkinson’s, others have found the opposite or no correlation. This heterogeneity between studies may reflect different well water contaminants and/or the varying geographical locations, and it remains unclear whether well water consumption can cause Parkinson’s or impact a person’s risk of developing the progressive disorder.

To investigate further, researchers based at the Nanjing Medical University, in China, conducted an analysis of current published studies — a meta-analysis — from Asia, Europe, and North America that examined the role of well water consumption and Parkinson’s risk.

The team searched the medical literature for related research published through October 2021 and selected a total of 15 case-control studies. Each compared Parkinson’s patients with people who do not have the nervous system disease.

Among the selected studies, 12 specifically evaluated the association between any well water consumption and Parkinson’s risk. Here, there was a 25% relative increase in disease risk. Notably, however, statistical analysis showed the variability between the selected reports was significant.

Examining hospital-based, case-control (HCC) studies alone found a 47% relative increase of Parkinson’s risk with well water consumption, but no association in population-based studies (PCC). The variability in the population studies was low but still high in hospital-based studies, according to the researchers, who say the results suggest “there may be other confounding factors leading to the heterogeneity.”

Assessed based on geographic area, studies in North America indicated no correlation between Parkinson’s and drinking well water. In contrast, Asian studies showed a 29% relative increase in risk, and in Europe, an 80% relative increased risk.

The variability in the North American and Asian studies was low but high in the European studies. “We considered that other heterogeneities were present in the included literature,” the team wrote.

A sensitivity assessment showed one study had a considerable influence on heterogeneity and, as such, it was removed from the analysis. Although heterogeneity was reduced after removing this study, it was still statistically significant. The pooled analysis of the remaining 11 reports showed a 16% relative increase in disease risk.

Hospital-based studies suggested a 31% relative increased risk of Parkinson’s in those exposed to well water. Again, there was no correlation found in population-based studies.

“As controls in HCC-design studies were more likely to go to a hospital, HCC-design studies can be more biased than PCC-design studies, which may lead to different conclusions,” the researchers wrote.

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Within this new analysis and according to geographical location, studies from North America did not find that the use of well water was related to Parkinson’s risk. Asian studies showed an increased risk of 29%, but studies from Europe were considered “unreliable owing to the high degree of heterogeneity,” the scientists wrote.

“When it comes to subgroup analysis by geographic area, although we consider that an association between well-water exposure and [Parkinson’s disease] risk cannot be established, we assume that the association between well-water use and [Parkinson’s disease] cannot be ruled out in a specific, small geographic area,” the scientists added.

A final test indicated there was no evidence of publication bias — when studies with positive findings are more likely to be published than those with negative results.

“It is not our final purpose to simply conclude that there is no significant correlation between well-water consumption and [Parkinson’s disease] risk, but why the impact of well water in different regions on [Parkinson’s disease] is different is what we most want to remind the public,” they added.

“This conclusion can be used as a reference for health systems when making policies,” the team concluded.

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