Enthusiastic golfers may unknowingly face an increased risk of a serious neurological condition due to their pastime.

Recent research indicates that exposure to a pesticide commonly applied on golf courses could potentially double the likelihood of developing Parkinson’s disease.

Affecting around one million individuals in the United States, Parkinson’s disease is a degenerative neurological disorder. It results from the deterioration of dopamine-producing nerve cells in the brain, leading to symptoms such as tremors, balance difficulties, muscle stiffness, and speech problems, all of which progressively worsen.

This condition appears to be becoming more prevalent in the U.S., with experts attributing the rise to environmental factors such as particulate matter (PM2.5) and pesticides.

Researchers from the University of California, Los Angeles (UCLA) have focused on the pesticide chlorpyrifos, which is utilized in agriculture, forestry, and maintained areas like golf courses.

The study examined over 800 individuals diagnosed with Parkinson’s and compared them to a similar number of people without the disease residing in California. Researchers assessed their historical exposure to pesticides and also tested the effects of inhaled chlorpyrifos on mice and zebrafish, the latter sharing approximately 70 percent of their genetic makeup with humans.

Researchers found long-term chlorpyrifos exposure led to a 2.5-fold increased risk of developing Parkinson’s disease compared to those who were not exposed. 

They also found mice exposed to the chemical developed movement issues and lost dopamine-producing neurons, both of which occur in Parkinson’s disease. 

Exposure to a pesticide used on US golf courses may double your risk of developing Parkinson’s disease, a new study suggests (stock image)

By exposing zebrafish models to the pesticide, researchers believe chlorpyrifos damages neurons by interrupting autophagy, the body’s natural cell recycling process that breaks down old cells to form new ones. 

Dr Jeff Bronstein, senior study author and professor of neurology at UCLA Health, said: ‘This study establishes chlorpyrifos as a specific environmental risk factor for Parkinson’s disease, not just pesticides as a general class.

‘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.’

The Parkinson’s Foundation estimates 1.2million Americans will be diagnosed with Parkinson’s by 2030, and 90,000 are struck by the disease every year. 

This is a 50 percent increase from the previously estimated rate of 60,000 a decade ago, the foundation estimates. 

There are roughly 35,000 deaths annually from the condition, often from aspiration pneumonia, caused by trouble swallowing, and severe injuries from falling.

Introduced in 1965, chlorpyrifos is one of the most widely used pesticides in the US. But in April 2021, the Environmental Protection Agency (EPA) announced it would ban the pesticide on food amid a mountain of studies suggesting even small amounts increased the risk of neurological conditions. 

However, a 2023 court ruling overturned the ban and allows agricultural use to continue, but states such as California, Hawaii and New York have introduced their own bans.

In California, where the new study took place, Governor Gavin Newsom in 2019 gave farmers until the end of 2020 to use up their remaining stock of chlorpyrifos. But because Parkinson’s largely affects older Americans, those in the study were likely exposed long before the state’s ban.

Chlorpyrifos is still permitted for use on US golf courses.

The European Union banned the use of chlorpyrifos in 2020, while the UK banned it in 2016.

Michael J Fox was diagnosed with Parkinson’s disease in 1991, revealing his diagnosis in 1998. In 2000, he founded the Michael J Fox Foundation to help fund Parkinson’s research

The new study, published last month in the journal Molecular Neurodegeneration, looked at data from 829 people with Parkinson’s disease and 824 without it, all of whom were part of UCLA’s long-running Parkinson’s Environmental and Genes study.

The team compared California’s state pesticide use reports along with participants’ home and work addresses to estimate their individual chlorpyrifos exposure over at least 30 years.

Participants were from three counties in central California: Kern, Fresno and Tulare. All of those with Parkinson’s were enrolled early in the disease progression, roughly three years on average after their diagnosis. 

Overall, there was a 2.5-fold increased risk of Parkinson’s in people who were exposed to chlorpyrifos the most compared to those with the least exposure over up to 30 years. 

The team also found that exposures occurring 10 to 20 years before disease onset were more strongly linked to Parkinson’s disease than the 10-year period prior to onset. 

In the mice studies, the rodents were exposed to aerosolized, or sprayed, chlorpyrifos in whole-body chambers for six hours per day, five days per week, over the course of 11 weeks. 

Football legend Brett Favre revealed he is battling Parkinson’s disease while speaking in front of Congress in 2024

The above graph shows the increase in Parkinson’s cases and deaths in the US 

They also underwent behavioral testing before exposure and three days after the last day of being in the pesticide chamber. Mice exposed to the pesticide performed worse on two out of the three behavioral tests than those in the control group, suggesting neurological issues.

Mice that inhaled chlorpyrifos on average suffered a 26 percent loss of tyrosine hydroxylase (TH) positive dopaminergic neurons, the main cells that produce dopamine. 

They also had inflammation in their brains and an accumulation of the protein alpha-synuclein, which clumps in Parkinson’s disease. 

Because chlorpyrifos exposure disrupted autophagy, the team believes treatments that target this process could prevent pesticide damage in the brain. 

The researchers also suggest people with known historical exposure to chlorpyrifos should be closely monitored for neurological conditions such as Parkinson’s.

The new study is one of several to suggest environmental factors could partly be to blame for the rise of Parkinson’s disease in the US. 

Researchers in Minnesota, for example, found exposure to the pollutant particulate matter, PM2.5, raised the risk of Parkinson’s disease by 36 percent. PM2.5, or fine particulate matter, refers to microscopic particles made of dust, soot, smoke and other chemicals which come from vehicle exhaust, industrial emissions and fires.

And Chinese scientists last year found being exposed to loud noises between 85 and 100 decibels, about as loud as a lawnmower or blender, for an hour a day could worsen signs of Parkinson’s such as movement difficulties and poor balance.  

There is no cure for Parkinson’s disease, but medications and other treatments can help replace lost dopamine and keep symptoms at bay. The most common, Levodopa, crosses the blood-brain barrier to convert itself into dopamine, controlling balance issues and tremors.