Researchers at UCLA's Fielding School of Public Health conducted a survey of 1,000 residents of central California, all adults age 35 and older. Of them, nearly 35 percent were diagnosed with Parkinson's disease, a disorder with symptoms such as tremors and loss of coordination. The study, released last week, found that those with Parkinson's were twice as likely as those without to report having suffered a head injury at some point, and having lost consciousness for more than five minutes.

Those with the disorder were also more likely to live within 500 meters of a location where the herbicide paraquat was used. Paraquat is used to kill weeds and plants.

Either condition could contribute to the development of Parkinson's disease; however, it seems when both factors are involved, the risk is higher. The reason for this appears to be that earlier head injury makes brain cells vulnerable to this particular poison used on plants. This is clearly something for those diagnosed with the disease to consider in their individual case.

While the findings aren't likely to influence advice physicians give to their patients, they'd likely advise avoiding both head injury and exposure to toxic chemicals anyway. This information is valuable in that those who have suffered a head trauma, especially one resulting in the loss of consciousness for five minutes or more, should be especially careful about exposure to paraquat.

The actual cause of Parkinson's disease remains unknown. However, the survey findings, published in Neurology, a medical journal, may help to increase awareness of some factors involved in the development of the disease. It cannot be concluded that the two factors specifically cause Parkinson's, but that a link clearly exists. The findings further serve to show that the cause -- or causes -- may be environmental at least in part, as opposed to solely genetic.

Source: ABC News, "Head Injury, Herbicide, Linked to Parkinsin's Disease in Survey," Lara Salahi, Nov. 13, 2012