Two researchers in Italy suggest exposure to pesticides and solvents is linked to a higher risk of developing Parkinson’s disease. They came to this conclusion after analyzing over 100 studies from around the world.
Parkinson’s is a progressive degenerative disease that affects a person’s ability to control and coordinate their muscle movement.
What can begin as a tremor in a little finger eventually leads to problems with speech and writing, and one day, inability to walk without help.
This deterioration is caused by the gradual reduction in brain levels of dopamine, a chemical messenger that carries signals to brain regions that control movement and coordination.
Exactly why Parkinson’s develops and how this affects dopamine production and maintenance is not known. But there is increasing evidence of an inherited or genetic component in a small proportion of cases.
One view that is gaining ground is that inflammation likely has a role in the development of Parkinson’s disease.
Dopamine is produced by a special type of brain cell, the dopaminergic neuron.
There is also a suggestion that certain compounds in the environment cause Parkinson’s by selectively destroying dopaminergic neurons. This latest analysis from Italy appears to add some weight to that view.
Emanuele Cereda from the IRCCS University Hospital San Matteo Foundation in Pavia, and Gianni Pezzoli of the Parkinson Institute – ICP in Milan, write about their findings in the 28 May print issue of the journal Neurology.
For their meta-analysis, a type of study that pools data from several studies of similar design, Cereda and Pezzoli reviewed results of 104 cohort and case-control studies that examined links between exposure to bug, weed, fungus and rodent killers, and solvents, and risk for developing Parkinson’s disease.
The research found that people exposed to bug or weed killers and solvents had an increased risk of developing Parkinson’s disease of between 33 to 80 percent compared to people who were not exposed to them.
And results from high quality case-controlled studies shows that exposure to paraquat (a herbicide) and maneb and mancozeb (fungicides), is tied to around a two-fold increase in risk of developing Parkinson’s.
The analysis also included studies that took into account how close people lived to the site of exposure (for instance urban or rural settings), their jobs, and whether their drinking water came from wells.
In a statement, Cereda says they also found “a link between farming or country living and developing Parkinson’s in some of the studies“.
And while they did not look at whether type of exposure, such as through the skin or inhaled, and type of application, such as spraying or mixing, affects the risk, Cereda says it appears that the risk “increases in a dose response manner as the length of exposure to these chemicals increases”.
The authors call for further prospective and high-quality case-control studies to prove whether these chemicals actually cause the higher risk of Parkinson’s disease.
They suggest these studies should also concentrate on specific chemicals.
Funds from the Grigioni Foundation for Parkinson’s Disease and the IRCCS University Hospital San Matteo Foundation helped finance the analysis.
In another recently published study, neurologists in Calofornia added the pesticide, benomyl, whose toxic effects still linger a decade after being banned by the US Environmental Protection Agency, to the list of pesticides linked to Parkinson’s.
Written by Catharine Paddock PhD