Pesticide Link to Parkinson’s ProbedApr 19, 2002 | MSNBC DOCTORS HAVE consistently observed that the neurodegenerative disease is more common in people who live in farming communities, leading them to speculate that exposure to pesticides increases a person’s risk of developing the disease. But little work has been done looking at the effects of specific compounds on people over time, said study co-author Dr. Samuel Goldman, a research scientist at the Parkinson’s Institute in Sunnyvale, Calif.
The question of the role of environmental factors in the development of Parkinson’s was thrown into the spotlight earlier this month when it was revealed that four people, including actor Michael J. Fox, who worked together at the Canadian Broadcasting Company in the late 1970s have developed the dreaded disease, which affects an estimated 1.2 million people in the United States and Canada.
“The idea of some link to environmental toxins is becoming pretty well-accepted, but the exact ones and how much you have to be exposed to be at risk of Parkinson’s disease isn’t clear,” said Dr. Robin Brey, a professor of medicine, division of neurology, at University of Texas Health Sciences Center, San Antonio.
Brey said that while this study doesn’t answer these questions once and for all, it suggests tantalizing links that need to be probed further.
For the study, a team of researchers surveyed over 20,000 farmers — 55 of whom reported having Parkinson’s disease — in the mid-1990s about their health history and exposures to specific pesticides.
Dr. Freya Kamel, an epidemiologist at the National Institute of Environmental Health, presented the initial findings to members of the American Academy of Neurology meeting in Denver this week.
The study found the use of several crop pesticides was more common among the Parkinson’s group than the non-affected farmers: dieldrin, paraquat, maneb, rotenone and a class of insecticides known as organochlorines.
Those with Parkinson’s were 80 percent more likely to have been exposed to dieldrin. The other pesticides appeared to carry an increased risk ranging from 20 percent to 60 percent.
These pesticides have been shown in test-tube studies or laboratory animal experiments to have toxic effects on certain brain cells, which can lead to Parkinson’s-like symptoms of tremor, rigidity, slowness of movement and imbalance.
Dieldrin, an insecticide, is now banned in the United States; rotenone, a pesticide, has been banned for agricultural use though it is still used to kill unwanted fish in reservoirs.
Paraquat, an herbicide, and maneb, a fungicide, are still used by farmers.
The study also found high-exposure methods of application, where the pesticide was likely to get on the skin or be inhaled, also were more commonly reported by the farmers with Parkinson’s.
But researchers do not think that exposure to these pesticides necessarily results in Parkinson’s disease.
“We don’t think any one compound causes Parkinson’s disease because then we would expect to see more clusters of cases,” said Goldman. “So it has got to be a whole lifetime of mild insults that set off a degenerative cascade in the brain.”
Most experts think that a complex interaction between a person’s genes and environmental exposures is at play in the development of Parkinson’s.
Kamel acknowledged that the data does not prove a relationship because it included only a small number of Parkinson’s patients and relied on self-reports of the disease, which may be inaccurate.
“It’s a very dirty study at this point,” Brey said. “Self-reports have a tremendous potential for bias. Many patients may have tremor and say they have Parkinson’s. The diagnosis clearly needs to be confirmed.”
Which is exactly what the research team plans to do. Noting that the new preliminary results come from the initial phase of an ongoing government-funded study of more than 84,000 pesticide applicators and their spouses, Kamel said the next step will be to identify more Parkinson’s patients, have neurologists confirm the diagnosis, and test their blood and homes for pesticide levels.
This major endeavor is widely hoped to definitively answer the question about the role of pesticide exposure in Parkinson’s, neurologists here said.
Researchers at the meeting also reported a potential link between eating a lot of foods that contain compounds known as isoquinolines (IQs) — such as chocolate, cheese, milk and wine — and Parkinson’s disease.
IQs have been shown in laboratory animals to inhibit cellular function and lead to Parkinson’s-like symptoms.
Goldman, who was lead author of this study, asked 72 pairs of twins in which one had Parkinson’s and the other did not about their dietary habits in the 10 years prior to one of them developing the disease.
He found those who ate a lot of chocolate — two to three candy bars per week — had more than a three-fold increased risk of having Parkinson’s than those who ate less. He also found a smaller link with wine and with a measure of total IQ consumption.
“The population is fairly small and the data is extremely retrospective,” he said. “But in basic science research there’s probably a reason to suspect these compounds.”
Brey noted that dietary histories are often unreliable. “People don’t remember what they’ve eaten years ago and if you had bad information you are going to have erroneous results.
“I would hate for someone to stop eating chocolate and cheese because of this study,” she said.