(HealthDay News) – The risk of developing Parkinson’s disease (PD) is higher for those with a traumatic brain injury (TBI) or exposure to the pesticide paraquat, and is three times higher for individuals with both TBI and paraquat exposure, according to a study published in the Nov. 13 issue of Neurology.

Noting that the combination of TBI with subthreshold paraquat exposure has been suggested to increase dopaminergic neurodegeneration in animals, Pei-Chen Lee, PhD, of the University of California at Los Angeles, and colleagues conducted a study involving 357 incident idiopathic PD cases and 754 population controls from central California to examine PD risk due to TBI and paraquat exposure.

The researchers found that subjects who reported TBI had a two-fold increase in the risk of PD (adjusted odds ratio [aOR], 2). There was a weaker association observed for paraquat exposure (aOR, 1.36). Participants exposed to both TBI and paraquat had a three-fold increased risk of developing PD compared with those exposed to neither risk factor (aOR, 3.01).

“While TBI and paraquat exposure each increase the risk of PD moderately, exposure to both factors almost tripled PD risk,” the authors write. “These environmental factors seem to act together to increase PD risk in a more than additive manner.”

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