Pesticides, Head Injury Possible Contributors to Parkinson's

--by Jenara Nerenberg

The Gist

If a family member of yours has Parkinson's disease, you may want to look into his or her history and ask about pesticide exposure and head injury. A new study appearing in the November 13, 2012, issue of Neurology suggests that people with these specific risk factors are three times more likely to develop Parkinson's.

The pesticide in question is called paraguat. It is a common herbicide used to control weeds, so people who live in agricultural areas are particularly at risk for toxic exposure. But when a person experiences a head injury in addition to pesticide exposure, that injury increases the person's susceptibility to Parkinson's because their body's cellular response to the pesticide is weakened.

The Expert Take

"While each of these two factors is associated with an increased risk of Parkinson's on their own, the combination is associated with greater risk than just adding the two factors together," said lead study author Dr. Beate Ritz, MD, PhD, of UCLA's Fielding School of Public Health.

Researchers do not know precisely which of the two risk factors first creates this vulnerability to Parkinson's, but their combined effect can be devastating for the human brain.

"This study suggests that the physiological process that is triggered by a head injury may increase brain cells' vulnerability to attacks from pesticides that can be toxic to the brain, or the other way around," Ritz said. "For example, chronic low dose exposure to pesticides may increase the risk of Parkinson's after a head injury."

The Takeaway

If you live near an agricultural area, be sure to check your local health department's website for a list of pesticides used on local crops. You and your family may be at risk for toxic exposure to paraguat. Furthermore, try to avoid situations where head injury may occur, and take precautions to protect your head, such as wearing a helmet when engaging in sports. 

Source and Method

A group of participants who lived in an agricultural area in Central California—357 people with Parkinson's and 754 people without—were involved in the study. Head injury was defined as loss of consciousness for more than five minutes, and exposure to paraquat was determined using a geographic information system (GIS) that measured the 500-meter area surrounding the homes and workplaces of the participants.

"People with Parkinson's disease were 36 percent more likely to have exposure to paraquat than those who did not have the disease," the study authors note. 

Other Research

A 2007 study conducted in five European countries and published in Occupational and Environmental Medicine concludes the same as above—that head injury and pesticide exposure can both lead to Parkinson's.

And a report published in October 2012 in Movement Disorders suggests that paraquat—the same pesticide examined in the above study—interacts with certain genes and increases the risk of Parkinson's. A second report followed in October 2012 that reinforces the theory of gene-environment interactions, but calls for increased research into the role of pesticides.