Pass on the Pesticides

With the fall harvest upon us, you are probably loading up on fresh produce from your garden or farmer's market. The extra effort you make to avoid pesticides now may pay off later in life. A new study finds that pesticides are linked to a greater risk of developing Parkinson's disease.

Parkinson's affects more than one million people in the U.S. and scientists have tracked its cause to a combination of genetic susceptibility and environmental factors. But what is in the environment that is causing this tremor-inducing disease? A number of previous studies have pointed to pesticide exposure. For example, a 2000 study of about 1,000 people found that those with Parkinson's were twice as likely to have used the chemicals around the home.

Most of these studies questioned Parkinson's sufferers about prior pesticide use, but such memories are not always reliable. The new study, which appeared in the July issue of Annals of Neurology, was much larger, with roughly 140,000 participants drawn from a study of cancer mortality that began in 1982. At that time, the individuals filled out a four-page survey detailing their current exposures to various chemicals. Researchers then followed the individuals for two decades to see if they developed the disease. This study design is much stronger since it doesn't rely on possibly faulty memories.

"The fact that people who reported exposure to pesticides had a significant increase in Parkinson's disease 10 to 20 years later really provides the compelling evidence that there is a real association," said Alberto Ascherio, M.D., Dr.PH. who conducted the study with colleagues at Harvard University. It takes five to 10 years for the disease to progress to a point where patients experience symptoms and seek treatment.

The study found that people who reported using pesticides had a 70 percent greater incidence of Parkinson's disease than those who were not exposed. The study also looked at other environmental factors like asbestos, formaldehyde and gasoline exhaust, but found no link to these or eight other environmental contaminants.

The study, however, didn't track which pesticides people had come in contact with. Most pesticides have never been tested for their association with Parkinson's symptoms. Studies in animals have found that pyrethroids, commonly found in household insecticides, and dithiocarbamates such as maneb may play a role in development of the disease. Two pesticides, a naturally occurring chemical called rotenone and the herbicide paraquat, have been found to induce changes in the brain that mimic Parkinson's. However, these studies often used doses that were higher than humans would be exposed to through the air, water or food.