Canadian researchers have found a higher risk of developing Parkinson's disease in people predisposed to the condition who are exposed to pesticides used in agriculture.
A link between exposure to pesticides and the onset of Parkinson's has been demonstrated by several studies over the past few decades. The first time this occurred was by chance in 1983, when a group of Californian scientists, analysing some cases of Parkinson's among drug users, noticed that many of them had used a drug adulterated with MPTP, a neurotoxin that causes the permanent symptoms of the disease. The researchers also noticed that the structure of MPTP was very similar to that of a herbicide, paraquat. Now the correlation between pesticides and Parkinson's is further confirmed by new research from the University of Guelph in Ontario, Canada.
The researchers revealed how pesticides such as paraquat and maneb can cause genetic mutations that lead to neurodegenerative diseases such as Parkinson's in predisposed individuals, doing so by investigating human cells — whereas until now the link between pesticides and the disease had been based primarily on animal studies and epidemiological research showing an increased risk among those exposed to agricultural chemicals. From two types of stem cells, the scientists created dopamine-producing neurons — the specific neurons affected by Parkinson's disease — and exposed them to the two chemicals. This exposure prevented the energy-producing mitochondria from moving to where they were needed within the cell, depleting energy in the neurons. The results of the study were published in the journal Federation of American Societies for Experimental Biology (Faseb): "For people who have a predisposition to the disease and who are exposed to these chemicals, a risk more than 250 per cent higher of developing Parkinson's disease compared to the rest of the population can be quantified," explained Scott Ryan, one of the study's authors and professor of molecular and cellular biology at the University of Guelph.
In 2012, France recognised Parkinson's as an occupational disease for farmers, establishing a causal link between the condition and exposure to pesticides. But studies on the subject continue: in 2017, researcher Sofiane Kab with the Institut national de la santé et de la recherche médicale (Inserm) became the first to calculate the incidence of the disease among farmers by comparing data from the Autorité Sociale Agricole, a health insurance system specific to the agricultural sector, with health insurance data from other sectors. The comparison revealed that farmers have a slightly higher risk — 13 per cent — of being affected by this neurodegenerative disease. Among retired farmers, this difference is even more pronounced, with 18 per cent more suffering from the disease compared to people of the same age group who worked in other occupations.
The study then sought to assess the risk associated with exposure to pesticides for people living in agricultural areas. "The frequency of this disease is indeed slightly higher among residents living near crops, especially in areas where the proportion of agricultural land devoted to viticulture is greater (+8.5 per cent)," Alexis Elbaz, neurologist and epidemiologist at Inserm and supervisor of Kab's thesis, explained to Le Figaro. "These results must, however, be confirmed by more specific studies on individuals, because there are numerous other risk factors for the disease."