WASHINGTON (Reuters) - The federal government said on Monday it was giving $20 million to three research centers to try to find out if chemicals or other environmental factors cause Parkinson's disease.

Farmers and other people exposed to pesticides seem to have a higher risk of developing the incurable brain disease, which slowly robs patients of their ability to move properly, but no one has been able to show a clear and irrefutable link.

"Our best chance for finding successful treatments for persons suffering with Parkinson's disease is to understand more about what triggers the disease," Dr. Kenneth Olden, director of the National Institute for Environmental Health Sciences, said in announcing the grants.

"Even better, this research may lead to ways to prevent Parkinson's disease in the first place."

The NIEHS, one of the National Institutes of Health, said it was funding the Parkinson's Institute in Sunnyvale, California, to examine risks associated with pesticides and heavy metals, the possibility that tobacco and caffeine may protect against Parkinson's, and genetic susceptibility to the disease.

Emory University researchers in Atlanta will look at the effects of pesticides in Parkinson's and develop new animal and laboratory models of the disease, while a team at the University of California Los Angeles will look at genes and pesticides.

"Evidence of an environmental link to Parkinson's is substantial," Joan Samuelson, president of the Parkinson's Action Network, which lobbies for funding to study the disease, said in a statement.