A common pesticide is linked to a higher risk of Parkinson's disease

If you have lived or worked near farmland for many years, the chemicals used on crops may affect your health in ways that only appear later. A study from UCLA Health, published in the journal Molecular Neurodegeneration, found that people with long-term residential exposure to a widely used pesticide called chlorpyrifos had more than 2.5 times the risk of developing Parkinson's disease compared with those who were not exposed.

Parkinson's disease gradually damages brain cells involved in movement. It often causes tremors, muscle stiffness, slowed movement, and difficulties with coordination. To understand this link, researchers examined information from 829 people diagnosed with Parkinson's disease and 824 people without the condition. They combined detailed pesticide application records from California with participants' address histories to estimate their exposure over time.

How does this pesticide harm the brain?

To see what happens inside the body, the team ran laboratory experiments on animals. They exposed mice to chlorpyrifos in aerosol form for 11 weeks to mimic how people might breathe in pesticides. The mice developed movement difficulties and lost neurons responsible for producing dopamine — a chemical messenger that helps the brain coordinate smooth movements.

Using zebrafish, the scientists discovered that chlorpyrifos disrupts autophagy, a natural cellular cleanup process. Think of autophagy as an internal recycling system that removes damaged proteins. When the pesticide blocked this system, harmful material accumulated inside nerve cells. However, when researchers restored the cleanup process or removed the abnormal protein buildup in their experiments, the neurons were protected from damage.

Does this mean the pesticide causes Parkinson's?

This population analysis shows an association, meaning it cannot prove that the pesticide directly caused the disease in these people. The protective effects seen in the laboratory models still need additional research to determine if they work in humans.

Chlorpyrifos has been used extensively in agriculture for decades. Its residential use was banned in the United States in 2001, and agricultural applications faced additional restrictions there in 2021. However, the pesticide remains in use on many crops in the United States and continues to be widely applied in other countries.

"This study establishes chlorpyrifos as a specific environmental risk factor for Parkinson's disease, not just pesticides as a general class," said Dr. Jeff Bronstein, professor of neurology at UCLA Health and the study's senior author. "By showing the biological mechanism in animal models, we've demonstrated that this association is likely causal. The discovery that autophagy dysfunction drives the neurotoxicity also points us toward potential therapeutic strategies to protect vulnerable brain cells."

Identifying specific chemicals linked to Parkinson's could help doctors monitor exposed individuals more closely and guide future treatments. If you notice unexplained tremors, unusual muscle stiffness, or new difficulties with coordination, talk to a doctor for an evaluation.