Growing Evidence That Pesticides Are Linked to Parkinson’s Disease

March 8, 2024
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Agricultural pesticides and herbicides have been tied to an increased risk of Parkinson’s disease in the Rocky Mountain and Great Plains region of the United States, according to a study that will be presented at the 76th annual meeting of the American Academy of Neurology in April.

Fourteen pesticides identified to have strong associations with Parkinson’s disease are most used in Colorado, Idaho, Kansas, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, Utah, and Wyoming.

Simazine, lindane, and atrazine were the most closely linked with Parkinson’s disease. The herbicide atrazine and insecticide lindane were associated with a 31 percent and 25 percent increased risk of developing the condition, respectively. Use of the herbicide simazine was linked to a 36 percent increased risk.

Researchers came to these conclusions by looking at nationwide data from 21.5 million Medicare beneficiaries who were at least 67 years old in 2009 and 465 pesticides included in the U.S. Geological Survey. They then zeroed in on 65 pesticides and determined their average annual application between 1992 and 2008 by county.

The more pesticides like simazine, lindane, and atrazine were used, the higher the rates of Parkinson’s disease among people living in those areas, the research team found.Parkinson’s Disease Prevalence on the RiseParkinson’s disease is one of the fastest-growing neurological disorders in the world. According to the Parkinson’s Foundation, nearly 90,000 people are diagnosed with Parkinson’s each year. The number has steeply increased from the previous 1980s diagnosis rate of 60,000 people per year. It is estimated that 1.2 million people will be living with Parkinson’s disease by 2030. The risk for Parkinson’s increases with age, and men are more often diagnosed than women.

The Parkinson’s Foundation reports that incident rates are higher in Rust Belt states and southern California, southeastern Texas, central Pennsylvania, and Florida. “Knowing this information will allow us to better serve people with Parkinson’s and their families and plan for adequate health care services in the future,” said Parkinson’s Foundation Chief Scientific Officer James Beck in a 2022 press release on the updated rates.Pesticides Long Known to Be Linked to Parkinson’s DiseaseThis latest study adds to an already growing body of evidence linking pesticides to Parkinson’s. A May 2023 study published in Nature Communications implicated long-term exposure to pesticides in Parkinson’s disease cases among cotton farm workers. The study, conducted by University of California–Los Angeles (UCLA) and Harvard University researchers, identified 10 pesticides directly toxic to specific neurons in the brain responsible for voluntary movement. Death of these neurons is a hallmark of Parkinson’s disease, according to a press release from UCLA Health.

According to the research team, since the discovery of a toxin called MPTP in 1976, much research has gone into how environmental pollutants, especially pesticides, affect Parkinson’s. MPTP is a neurotoxin that deteriorates the part of the brain responsible for motor movement and reward functions. This deterioration is likely responsible for the classic symptoms of Parkinson’s disease, including tremors, stiffness, and slowed movements. MPTP shares structural similarities to pesticides such as paraquat.

Despite pesticides’ known toxicity and risk to human health, many are used readily in the United States today. According to the Environmental Protection Agency (EPA), which regulates pesticide use, “The health effects of pesticides depend on the type of pesticide. Some, such as the organophosphates and carbamates, affect the nervous system. Others may irritate the skin or eyes. Some pesticides may be carcinogens. Others may affect the hormone or endocrine system in the body.” The EPA determines if a pesticide is harmful and publishes the amount allowed in water in its Human Health Benchmarks for Pesticides table online.

Amie Dahnke

Amie Dahnke is a freelance writer and editor residing in California. She has covered community journalism and health care news for nearly a decade, winning a California Newspaper Publishers Award for her work.

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