30
Jun
Study Associates Exposure to Pesticide Mixtures with an Increase in Alzheimer’s Disease Prevalence
(Beyond Pesticides, June 30, 2026) A peer-reviewed article, published in Scientific Reports, focuses on the link between exposure to pesticide mixtures and Alzheimer’s Disease (AD) prevalence at the county-level across the United States. Alzheimer’s, a type of dementia that affects memory, thinking, and behavior, accounts for 60-80% of dementia cases.
In conducting a novel cross-sectional analysis of data on pesticide application intensity and disease prevalence, the researchers, from the Medical University of South Carolina, are able to identify exposure clusters with significant associations to the occurrence of AD. The strongest positive associations, where AD prevalence increases as pesticide exposure increases, are “observed for a soil fumigation/nematicide system, an herbicide-dominant vegetation control regime, and a neuroactive insecticide system,” the authors note. These findings link pesticide mixtures to increased AD rates. (See the full PDF of the study here.)
Study Importance and Background
AD is a condition that gradually damages and destroys neurons in the brain, with disproportionate risks across the U.S. in certain geographical areas. (See here and here.) “These spatial patterns suggest that contextual and environmental determinants may contribute to disparities in dementia burden beyond established individual-level risk factors,” the researchers state. They continue, “Although AD dementia is the leading cause of dementia worldwide and currently affects more than seven million older adults in the U.S., its environmental drivers remain incompletely characterized.”
The existing literature focuses on individual active ingredients, while an agricultural pesticide application rarely occurs in isolation, and these analyses fail to evaluate the additive or synergistic effects of mixtures. As the authors highlight: “[M]odern agricultural datasets include hundreds of active ingredients, creating an exposure space characterized by significant intercorrelation… As a result, associations attributed to individual compounds may instead be indicative of unaccounted for co-application schemes and regional agricultural practices.”
To address this data gap, the current study uses county-level pesticide exposure patterns across the U.S. in relation to AD dementia prevalence to analyze pesticide mixtures. “Through this mixture-aware approach, we seek to provide a structured understanding of how agricultural pesticide exposures may contribute to geographic variation in AD dementia prevalence across the U.S. and highlight potentially modifiable environmental risks relevant to public health policy and prevention strategies,” the researchers state.
Methodology and Results
Over 3,000 data points for county-level estimates of AD dementia prevalence are utilized in this study, derived from the neuropsychological assessments through the Chicago Health and Aging Project (CHAP), while county-level agricultural pesticide use data was obtained from the U.S. Geological Survey National Pesticide Synthesis Project. Pesticide estimates from 2010 to 2018 are incorporated, capturing 462 unique pesticide active ingredients.
After assembling the data on disease prevalence and pesticide exposures, the pesticides were screened and analyzed for consistent associations with AD. The selected pesticides were then grouped into correlated exposure clusters for further analysis. As a result, 20 clusters are significantly associated with AD dementia prevalence.
AD develops over decades, which the authors point out is a limitation of the study, saying, “[T]he current cross-sectional analysis may not fully capture the long-term neurodegenerative effects of pesticide exposure, and observed associations may reflect both recent and historical exposures.” While potentially underestimated, the findings do show a nationwide association between pesticide mixtures and AD prevalence. “Our findings demonstrate that by evaluating pesticide exposures as coordinated mixtures instead of individual compounds, we can better resolve the agricultural and land-use contexts that shape real world exposures,” the authors conclude.
Previous Research
As cited in the current study, a growing body of evidence “suggests that broader environmental factors may contribute to population-level patterns of cognitive decline.” Research shows that environmental contaminants are associated with an elevated risk of AD. (See scientific literature here.) “Within this environmental context, exposure to pesticides is of particular concern because of their widespread agricultural use and neurotoxicity,” the authors state.
As pesticides are often designed to disrupt critical neurobiological processes such as neurotransmission, mitochondrial function, and cell division, these compounds are linked to deleterious effects such as oxidative stress, neuroinflammation, and direct neuronal damage. (See here and here.) Studies examining pesticide mixtures also find that combined exposures lead to synergistic neurotoxicity that is greater than effects from individual compounds. (See research here and here.)
Research on population-based investigations, such as the French PAQUID (“Personnes Âgées Quid” or elderly) cohort (landmark epidemiologic study) and the U.S. Agricultural Health Study, report “significant associations between occupational pesticide exposure and neurodegenerative outcomes in extended follow-up analyses.” (See studies here, here, here, and here.) In another study of AD risk, increased risks among individuals with occupational organophosphate and organochlorine pesticide exposure are seen in an agricultural community cohort. Analyses of biomarkers “have linked elevated serum organochlorine pesticide levels to a higher likelihood of AD dementia diagnosis.”
As shared in recent Daily News coverage, entitled Pesticide Exposure Again Linked to Neurotoxic Effects in Humans and Wildlife in Comprehensive Review, a study in Discover Toxicology highlights neurotoxic pollutants as significant environmental threats, showcasing the adverse impacts on vertebrates’ neurological health from pesticides, including organophosphates, carbamates, and organochlorines. “These substances disrupt normal neurophysiological functions by impairing neurotransmission, generating oxidative stress, provoking neuroinflammation, and initiating neuronal cell death,” the authors say. They continue, “Such disturbances are linked to cognitive deficits, motor impairments, and abnormal neural development.”
This review mentions the “cocktail effect,” which refers to the combined or interactive effects of multiple contaminants that can be additive (total effect equals the sum of each individual effect) or synergistic (total effect is greater than the sum, amplifying toxicity). With this increase in toxicity as multiple pesticides are encountered as mixtures, further health threats occur.
Daily News, Cross-Sectional Study Finds Connection Between Pesticide Exposure and Alzheimer’s Disease, documents a 2024 study published in Psychiatry Research of individuals living near chemical-intensive agricultural environments with heightened risks of Alzheimer’s disease relative to the general population. This finding builds on existing peer-reviewed studies that document the relationship between chronic pesticide exposure and elevated risk of neurodegenerative disorders including Alzheimer’s disease, as well as Parkinson’s disease, dementia, multiple sclerosis (MS), and Huntington’s disease. (See additional coverage on Alzheimer’s here.)
A Path Forward
As documented in the Pesticide-Induced Diseases Database, the nervous system is an integral part of the human body and includes the brain, spinal cord, a vast network of nerves and neurons, all of which are responsible for a majority of bodily functions—from senses to movement. However, exposure to certain chemicals, like pesticides, can cause neurotoxic effects or exacerbate preexisting chemical damage to the nervous system. The impacts of pesticides on the nervous system, including the brain, are extremely hazardous, especially for chronically exposed individuals or during critical windows of vulnerability and development. With the mounting evidence of pesticide-induced neurological diseases, including amyotrophic lateral sclerosis (ALS) and Parkinson’s disease, along with cognitive function and dementia-like diseases like Alzheimer’s, the solution lies in the elimination of petrochemical pesticides and synthetic fertilizers.
Join the organic movement by buying organic products (on a budget!), growing your own organic food, and taking action through Action of the Week, where you can have your voice heard on governmental actions that are harmful to the environment and public and worker health, increase overall pesticide use, or undermine the advancement of organic, sustainable, and regenerative practices and policies. >> Tell Congress, FDA, and EPA that it is past time to stop the manufacture and use of all organophosphate pesticides, which damage the nervous system and brain at low levels.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Wang, L. et al. (2026) Agricultural pesticide use and Alzheimer’s disease dementia prevalence across US counties in a mixed supervised–unsupervised analysis, Scientific Reports. Available at: https://www.nature.com/articles/s41598-026-55678-4.
