WASHINGTON (UPI) -- People exposed to pesticides are at a higher risk of developing Parkinson's disease, according to the longest and largest study yet to support such a connection.
Study participants who reported regular exposure to pesticides had a 70 percent higher incidence of the disease than those who were not exposed to the chemicals.
"This is the first fairly clear evidence that some chemical exposure significantly increases risk for Parkinson's," said lead author Dr. Alberto Ascherio, an associate professor of nutrition and epidemiology at the Harvard School of Public Health.
"With the combined evidence of all the studies in humans ... it's extremely unlikely there is another explanation," he said.
The study will appear in the July issue of the Annals of Neurology.
Ascherio and colleagues surveyed men and women from the Cancer Prevention Study II Nutrition Center, a longitudinal group organized by the American Cancer Society.
An initial survey was done in 1982 and repeated in 1997, 1999 and 2001. The more than 140,000 responders to the 2001 survey did not have signs of Parkinson's disease before 1992. The researchers looked at the medical records of study participants who reported getting Parkinson's after 1992. Just over 7,800 people reported exposure to pesticides, and 413 people developed Parkinson's disease, a neurodegenerative disorder that affects up to 1.5 million Americans, most of them older than 65.
People who reported exposure to pesticides were 14 times more likely to list their occupation as farmer, rancher or fisherman, the authors wrote. Even so, after analysis both farmers and non-farmers demonstrated the same increase -- 70 percent -- in Parkinson's incidence. Ascherio suspects the non-farmers represent people using pesticides around their home and garden.
Previous studies linking pesticides to development of Parkinson's were inconclusive, largely because the researchers asked participants to draw on their memory of past experience, which lends itself to error, the authors wrote. In the new study, incorporating medical record review of the survey data strengthened its authenticity.
Pesticides are a neurotoxin, designed to disable the brains of insects. Although scientists know the nervous systems of people are wired similarly to insects, they're not sure exactly how pesticides affect the human brain. One theory is the chemicals promote the aggregation of a protein, alpha synuclein, in the brain. When clustered on brain cells, this protein can cause Parkinson's and other neurodegenerative disorders.
The authors concede the study lacks detailed information about the duration and intensity of pesticide use, as well as which of the dozens of brands of pesticides are more harmful. Past studies have suggested chronic, low-dose exposure to pesticides raises the likelihood of getting Parkinson's.
Ascherio plans to identify the specific types of pesticides that might be most dangerous to health. He also wants to research genetic variations in how people respond to pesticides. Some individuals possess genes that enable them to metabolize pesticides very easily, perhaps staving off Parkinson's, while others are more genetically susceptible to the chemicals. Figuring out the molecular pathways of the disease could help someday prevent its progression.
The study affirms what a lot of people have thought, said Dr. J. Timothy Greenamyre, director of the Pittsburgh Institute for Neurodegenerative Diseases at the University of Pittsburgh.
"It's the best prospective study they've done so far," said Greenamyre, who works on animal models and the interaction between environmental toxins and genes.
There also could be an interaction between pesticides and the many genetic defects that bring on Parkinson's, Greenamyre added. For example, the people who were exposed to pesticides and developed Parkinson's may have a separate, identifiable genetic makeup than those who didn't, he said.
Angie (ontario canada zone 5)
The love of gardening is a seed once planted
and germinated; can never be destroyed.
---------------------------------
Make free worldwide PC-to-PC calls. Try the new Yahoo! Canada Messenger with Voice
