Link Between Parkinson's and Pesticides

Fruit's good for you, right? Not always. The link between pesticides and Parkinson's.

By Willow Lawson, published on May 20, 2003 - last reviewed on August 30, 2004

Fruit is good for you. Ask any nutritionist or doctor. It's packed with vitamins, fiber and antioxidants, which ward off many chronic diseases.

But fruit may have a darker side. A daily diet that includes lots of fruit or fruit juice has been linked to Parkinson's disease, a disorder of movement characterized by rigid muscles and tremors in the limbs. It's the disorder Michael J. Fox has, though it more usually strikes the elderly.

Pesticides or some other toxin in fruit may be the culprit, says Andrew Grandinetti, Ph.D., assistant research professor at the University of Hawaii's Pacific Biomedical Research Center. He recently presented his findings at the annual meeting of the American Academy of Neurology in Honolulu in April.

"People should not stop eating fruit," he insists. "But it's always wise to wash it, for many reasons. The link to pesticides is merely conjecture, but it's reasonable to think that fruit may be a marker of pesticide use."

Parkinson's disease involves a loss of brain cells in the substantia nigra, an area of the brain that produces the neurotransmitter dopamine. Dopamine allows smooth movement of muscles but also affects mood, motivation, attention and learning.

People with Parkinson's--over one million Americans--have a severe shortage of dopamine. The disease may appear at any age, but is more common after the age of 30, and the risk increases with age. Parkinson's occurs all over the world, affecting more men than women. It is typically accompanied by such other symptoms as depression, sleep disturbance, constipation, dementia and problems breathing and swallowing.

Agricultural poisons have been fingered before with regard to Parkinson's. In 2000, a Stanford University study linked Parkinson's risk to exposure to pesticides in the course of work, such as on the farm. The same study also linked insecticide exposure in the home and garden to a 70% increase in risk of the disorder. Researchers believe these poisons may kill specific brain cells.

Chemicals are also suspected triggers of other neurological disorders. A $9 million project at the University of California at Davis called the M.I.N.D. Institute (for Medical Investigation of Neurodevelopmental Disorders) is currently examining whether environmental contaminants such as mercury, PCBs, and heavy metals play a role in autism. The number of cases has recently surged in California.

"A child's nervous system undergoes immense remodeling during the early parts of life," says Isaac Pessah, Ph.D., professor of molecular biosciences at UC Davis School and principal investigator of the autism research center. There is reason to believe the development of the nervous system could be interrupted in subtle and not so subtle ways by environmental toxins. Results of the various studies are still several years away.

Grandinetti believes that toxins produced by plants themselves might also be at the root of the link between fruit and Parkinson's. Plants ordinarily produce toxic substances to protect themselves from insects. Many foods, including raw peanuts, potatoes, as well as many others, can be toxic to humans as well unless cooked or otherwise modified.

"Food toxins are always there, but they are usually at acceptable levels," says Grandinetti. It may be that they are tied to Parkinson's disease by some "compounding factor that we haven't measured."

The Hawaii study wasn't designed to focus on Parkinson's disease. It was intended to scrutinize heart disease and compare rates among men born in Japan and those of Japanese descent living in Oahu. It began in 1965 with 8,000 men aged 45 to 68. So far, 141 of them have developed Parkinson's.

The study is notable because it has actually tracked dietary intake over decades, rather than relying on subjects' memories of what they ate. Further, the study began recording dietary information late in life.

Although the actual cause is still unknown, neuroscientists have long thought that Parkinson's is triggered by environmental factors. An increased rate of the disease has also been linked to dietary fat and sugar intake and use of the drug ecstasy. Other studies have also shown a genetic predisposition to Parkinson's and other diseases like autism.

It's not all bad news, however. Some studies have found that even some unhealthy behaviors may have their good side, at least with regard to Parkinson's disease. A study in Rotterdam, the Netherlands, found that people who smoke seem to lower their risk of Parkinson's by half. Those who drank coffee and alcohol also had lower risks.

But it may not be as simple as cause and effect. People who engage in "novelty-seeking behaviors" like smoking and drinking might have naturally higher levels of dopamine to begin with, which may protect them from some neurological disorders.