Exposure to pesticides is linked with increase in risk of Parkinson's disease, a new study has found.

Parkinson's disease occurs when the part of the brain that controls movement doesn't function properly. This usually happens when the neurons that produce a chemical dopamine - that regulates body movements - die. The symptoms of the disease include trembling hands or legs, stiffness, poor balance and co-ordination between hands and legs, slow movements. PD usually affects men more than women. Although the disease starts usually after 60 years of age, it can occur earlier as well.

The present study was conducted by Gianni Pezzoli, MD, from the Parkinson Institute, Istituti Clinici di Perfezionamento in Milan, and Emanuele Cereda, MD, PhD, IRCCS University Hospital San Matteo Foundation in Pavia, Italy. Researchers found that exposure to weed/pest killers increased the risk of developing the disease by 33 to 80 percent. 

For the study, researchers looked at 104 studies on the subject from around the world. These studies included data on people's exposure to weed, fungus, rodent or bug killers, and solvents as well proximity of exposure such as living on a farm versus living in the city.

"Due to this association, there was also a link between farming or country living and developing Parkinson's in some of the studies," said Emanuele Cereda, author of the study.

Researchers found that an exposure to weed or bug killers increased the risk of developing Parkinson's disease by 33 percent to 80 percent. Also, paraquat (weed killer) or the fungicides maneb and mancozeb increased the risk of PD by two times.

"We didn't study whether the type of exposure, such as whether the compound was inhaled or absorbed through the skin and the method of application, such as spraying or mixing, affected Parkinson's risk," said Cereda in a news release. "However, our study suggests that the risk increases in a dose response manner as the length of exposure to these chemicals increases."

At present, there is no cure for Parkinson's disease, but a variety of medications provide dramatic relief from the symptoms, according to National Institute of Neurological Disorders and Stroke.

The study is published in the journal Neurology.