The link between Parkinson’s disease and farming or occupational exposure to pesticides is well documented in the scientific literature. This is why, in France, since 2012, Parkinson’s disease can, under certain conditions, be recognized as an occupational disease among farmers. However, there were no national French studies available to estimate the excess risk of Parkinson’s disease in this population. As for motor neuron disease, studies on the role of pesticide exposure or farming are much fewer in number, and their results are inconsistent. We focused on the farming population because it is characterized by frequent occupational use of pesticides, some of which may have neurotoxic properties.

Furthermore, it is possible to study the agricultural population using medical-administrative data because there is a health insurance system specific to the agricultural sector managed by the Mutualité sociale agricole (MSA). In 2012, the MSA covered approximately 3.4 million people (5% of the French population), of whom 48% were farm owners and 52% were employees (one-third of whom were agricultural workers).

Using health insurance data (drug reimbursements, long-term conditions) and hospitalization records, we identified, in a consistent manner across the entire metropolitan territory, individuals with these two neurodegenerative diseases (Parkinson’s disease in 2011 and 2012, motor neuron diseases between 2010 and 2014). The validity of this approach has been evaluated in previous specific studies.

The objective of the study was to determine whether there was an association between working as a farmer and the onset of Parkinson’s disease or motor neuron diseases. To do this, we compared the incidence (number of new cases per year relative to the at-risk population) of these two neurodegenerative diseases among MSA members with that of other health insurance schemes.

Among the farming population, we identified approximately 2,500 new cases of Parkinson’s disease and 150 new cases of motor neuron disease each year.

Our study confirms the association between farmer status and Parkinson’s disease.
The incidence of the disease was 13% higher among farmers affiliated with the MSA than among those affiliated with other schemes, after adjusting for differences in age and sex between these two populations. This difference was even more pronounced (+18%) among individuals aged 60–84. It was also higher (+10%) among farmers compared to MSA employees.

The incidence of the disease among MSA employees was similar to that among those affiliated with other health insurance plans.

These differences persisted after accounting for smoking. Our interpretation is that these results are, at least in part, explained by the role of occupational exposure to pesticides.
However, we cannot rule out the possibility that other characteristics of farm owners play a role.

Farmers are, on average, more exposed to pesticides than agricultural employees.
The latter constitute a very heterogeneous group. About one-third are farm laborers. The others hold administrative positions (for example, administrative staff at agricultural cooperatives) and, for the most part, are not exposed to pesticides in the course of their work.

As for motor neuron diseases, our results suggest a weaker association than for Parkinson’s disease. The incidence of these conditions was 8% higher among farmers than among individuals enrolled in other health insurance schemes (a result bordering on statistical significance). As before, the role of occupational exposure to pesticides could be considered. For these analyses, we faced two challenges.
On the one hand, given the low incidence of these conditions and despite the study’s national scope, the analyses were based on a smaller number of cases than for Parkinson’s disease; it will therefore be worthwhile to replicate this analysis when more data become available. On the other hand, it has been shown that farmers smoke less than the rest of the population. However, there is uncertainty regarding the existence of an association between smoking and motor neuron diseases.
Having more precise data on this issue would allow for more robust conclusions.

The study’s findings confirm that the agricultural workforce is at a higher risk for Parkinson’s disease and motor neuron diseases. With regard to Parkinson’s disease, the results underscore the importance of recognizing Parkinson’s disease as an occupational disease among agricultural workers exposed to pesticides.

Further studies will be launched in collaboration with Inserm to assess whether epidemiological tools such as crop/exposure matrices (tools that track the evolution of pesticide treatments over time and space according to crop type) could help identify one or more substances associated with an increased risk of Parkinson’s disease among agricultural workers. These results will be essential for identifying preventive measures to be implemented.

Furthermore, the issue of pesticide exposure led us to examine the role of pesticide exposure in a non-occupational context. To better characterize potentially at-risk situations or populations, we studied the association between types of agricultural crops and the incidence of Parkinson’s disease. We found a slightly higher incidence among people living in the most agricultural cantons, particularly in those where the proportion of farmland allocated to viticulture is highest. This finding highlights the issue of pesticide exposure among residents living near agricultural areas, which Santé publique France is addressing through a study aimed at characterizing multi-site exposure among residents living near agricultural crops.