Washington, DC–(ENEWSPF)–November 14, 2012. For years, scientists have shown that pesticide exposures are linked to the onset of Parkinson’s disease. Now a new study by researchers at University of California, Los Angeles, (UCLA) finds that exposure to pesticides and suffering a head injury are associated with a three-fold increase in one’s chances of developing Parkinson’s disease.
Parkinson’s disease is the second most common neurodegenerative disease, and occurs when nerve cells in the substantia nigra region of the brain are damaged or destroyed and can no longer produce dopamine, a nerve-signaling molecule that helps control muscle movement. People with Parkinson’s disease have a variety of symptoms, including loss of muscle control, trembling and lack of coordination. Over time, symptoms intensify. At least one million Americans have Parkinson’s and about 50,000 new cases are diagnosed each year.
The study, “Traumatic brain injury, paraquat exposure, and their relationship to Parkinson disease,” published in the journal Neurology surveyed more than 1,000 adults ages 35 and older who lived in central California. Some 357 of the participants were diagnosed with Parkinson’s disease. Participants with the disease were nearly twice as likely as those without the disease to report having had a head injury in which they lost consciousness for more than five minutes. Forty-two Parkinson’s patients, or 12 percent of that group, reported receiving a head injury that knocked them unconscious for five or more minutes, as compared to 50 people in the non-Parkinson’s group, or seven percent. The Parkinson’s patients are nearly twice as likely to have had such injuries. Using a geographical tracking system, the researchers also found that those with Parkinson’s disease were also more likely to live within 500 meters of a spot where the herbicide paraquat was used. Parkinson’s patients are 36 percent more likely to be exposed to paraquat, which is toxic to both humans and animals. Nearly half of the study subjects with Parkinson’s had been exposed to paraquat, as opposed to 39 percent of the non-Parkinson’s subjects.
“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,” Beate Ritz, MD, PhD, lead author of the study, said in a public statement. Dr. Ritz says her work suggests that a head injury may trigger a physiological process that increases brain cells’ vulnerability to attacks from toxic pesticides, or vice versa. Constant low-dose exposure to pesticides could place a person at greater risk for Parkinson’s to strike after a head injury.
While there are no definitive causes for Parkinson’s disease, this study is one of many to suggest that environmental influences, like exposure to pesticides, not just genetic variations, may be likely triggers in some cases. Pesticides are long suspected of being tied to Parkinson’s, at least in part, because of the high rate of the disease among farmworkers. Farmworkers have nearly double the risk for the disease if exposed to pesticides, with a dose-effect for the number of years of exposure. Exposure to the pesticides, paraquat and maneb, within 500 meters of an individual’s home, has been shown to increase the risk of developing Parkinson’s by 75 percent, according to a University of California, Berkeley study. The Institute of Medicine (IOM) found suggestive but limited evidence that exposure to Agent Orange and other herbicides used during the Vietnam War is associated with an increased chance of developing ischemic heart disease and Parkinson’s disease in Vietnam veterans. Another publication found that rural residents who drank contaminated well water had an increased (up to 90 percent) risk of developing Parkinson’s. French researchers also found that among men exposed to pesticides such as DDT, carriers of the gene variants are three and a half times more likely to develop Parkinson’s than those with the more common version of the gene. Last year, researchers at the University of Missouri School of Medicine took some of the first steps toward understanding the link between pesticides and Parkinson’s, and unraveling the molecular dysfunction that occurs when proteins are exposed to environmental toxicants.
Previous work has shown a link between the pesticides, rotenone and paraquat, and Parkinson’s disease. One study found that people who used either pesticide developed Parkinson’s disease approximately 2.5 times more often than non-users. Scientists have also been aware for many years that both paraquat and rotenone are neurotoxicants that, when given to animals, reproduce features of Parkinson’s in the brain. Paraquat is known to increase the production of certain proteins in the brain that damages cells that produce dopamine. People with Parkinson’s have a dopamine shortage that causes the motor problems, muscle tremors, and rigidity that characterize Parkinson’s. Rotenone inhibits the function of mitochondria in the brain, which is responsible for regenerating certain brain cells. Both pesticides are largely restricted, due to concerns about links to Parkinson’s. Paraquat is restricted to certified applicators and rotenone is only permitted to kill invasive fish species.
For more information, read Beyond Pesticides’ report “Pesticides Trigger Parkinson’s Disease,” a review of published toxicological and epidemiological studies that link exposure to pesticides, as well as gene-pesticide interactions, to Parkinson’s disease.
The Pesticide-Induced Diseases Database captures the range of diseases linked to pesticides through epidemiologic studies. The database, which currently contains hundreds of entries of epidemiologic and laboratory exposure studies, will be continually updated to track the emerging findings and trends.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.