This common pesticide may have a link to Parkinson’s disease, study says

Researchers from UCLA looked at patients in California’s Center Valley.
Tractor on farm

A common pesticide called paraquat may lead to Parkinson's disease, according to UCLA researchers. Their recent study suggests that paraquat, used in places such as California's Central Valley, can cause the movement disorder.

The idea that paraquat may cause Parkinson's disease is not a new one. It has been studied since the late 1980s, notes Beate Ritz, MD, PhD. Dr. Ritz, the study's senior author, is a distinguished professor of epidemiology, environmental health and neurology, and holds co-appointments at the David Geffen School of Medicine and UCLA’s Fielding School of Public Health.

Many studies have shown that paraquat can harm animals, says Dr. Ritz. But there have been fewer human studies.

Study details

California farmers have long used paraquat, notes Dr. Ritz. 

"Our study is based on pesticide application records and proximity of residents and workers to such applications," she explains.

As well as putting out calls for patients with Parkinson's disease for the study, researchers also used data from a California Parkinson's disease registry pilot program from 2009 to 2016.

The study included 829 patients with Parkinson's disease and 824 people living in the same counties who don't have Parkinson's disease. The researchers looked to see if paraquat was used at or near their homes and workplaces.

"We included applications on fields within 500 meters of the addresses between 1974 and the year they got Parkinson's disease," says Dr. Ritz. "We used a similar date for the people who don't have Parkinson's disease."

Finding an increased risk

The researchers found a strong connection between the pesticide and Parkinson's disease risk. The risk went up the longer they were exposed and also with the amount of pesticide that was applied on fields.

"The effect estimates were particularly strong for patients who got Parkinson's disease before the age of 60. It was also seen for those who got it later in life," Dr. Ritz says.

The results were consistent no matter how they looked at the data, says Dr. Ritz. "In smaller studies, we often see effects fluctuate more when we slice the data in different ways," she notes.

Dr. Ritz hopes the Environmental Protection Agency will ban paraquat in the U.S. Most other countries have long banned its use, she notes.

"In fact, it has been banned from use in the U.K., where it is being made.”

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