NEWS2U Health & Wellness
Living Healthy in an Unhealthy World

Wednesday, June 28, 2006

More evidence suggests pesticides cause Parkinson's disease

By Ben Wasserman
June 26, 2006

People who use pesticides on their farms or backyards or homes should take note that exposure to pesticides is likely to raise their risk of developing Parkinson's disease later in life, suggests a new study.

The study reported in the July issue of the Annals of Neurology found that the risk of Parkinson's disease in those who reported being exposed to pesticides and herbicides increased by about 70 percent, ten to 20 years after initial exposure.

The finding resulted from data extracted from surveys of more than 140,000 men and women who took part in the Cancer Prevention Study II Nutrition cohort that began in 1992.

The team led by Alberto Ascherio, M.D., Dr.Ph., of the Harvard School of Public Health found that the risk of Parkinson's disease is highest among people with occupational exposure to pesticides such as farmers. The risk was also found in those who were exposed to pesticides used in gardens and backyards.

However, the risk of Parkinson’s was not associated with exposure to other occupational exposures such as asbestos and dust, according to the study.

The risk of Parkinson's disease associated with exposure to pesticides has been reported in many studies. One recent study was reported by Mayo Clinic researchers who published their finding in the online June issue of Movement Disorders.

In the study, they found that men who had ever been exposed to pesticides on their farms or gardens were more than twice as likely to develop Parkinson's disease compared to men who was not exposed to the toxic chemicals.

However, Walter A. Rocca, M.D., M.P.H. and colleagues who conducted the study were unable to figure out the effect of intensity and duration of pesticide exposure on the risk of Parkinson's disease because complete data on the dosage and exposure duration were not available.

Both studies found high risk of Parkinson's disease in both farmers and non-farmers who were exposed to pesticides. But other occupational risk factors were not associated with the disease.

In the Harvard study, among 143,325 who responded to study surveys in 2001 and who were not diagnosed with Parkinson's disease or symptoms at the time the survey began, 5.7 percent or a total of 7,864 participants including 5,203 men and 2,661 women reported exposure to pesticides.

Researchers found that 1,956 farmers, ranchers, or fishermen were fourteen times more likely to be exposed to pesticides compared with people in other occupations. Blue collar workers had a two-fold higher risk of exposure to pesticides.

Even after adjustment of other risk factors including age, gender, and smoking status, the risk of Parkinson's disease was still significant among those who were exposed to pesticides, 1.7 times higher than that for those who were not exposed.

The duration of pesticide exposure did not seem to change the risk. Among those who did report the duration, the risk of Parkinson's disease was not significantly different between those who had been exposed to pesticides for more than a decade and those for less than ten years, with the relative risk 2.3 for the former and 2.1 for the latter.

Although the study was based on the statistical correlations and a cause-effect association could not be established, exposure to pesticides is likely to harm the brain as the pesticides commonly used in the U.S. have been shown to cause degeneration of dopaminergic neurons in the brain, causing neurologic adnormalities in animals who received high doses of pesticides, according to the authors.

Also in postmortem studies, other researchers have found that high levels of organochlorine pesticides were present in the substantia nigra or striatum of patients with Parkinson's disease, indicating that these pesticides are persistent in tissues years or even decades after exposure.

Evidence that organochlorines damage the brain of patients with Parkinson's disease was also found in autopsy studies as cited by the authors. The presence of these pesticides in Parkinson's patients seems to be unique as they were not detected in other similar degeneration diseases such as Alzheimer’s disease.

Organochlorine pesticides such as DDT, chlordane, lindane and toxaphene are persistent in the environment. Some of such pesticides such as DDT have been banned in many countries, but they are still polluting the environment.

Other than biochemical evidence, many epidemiologic studies have linked exposure to pesticides to Parkinson’s disease.

One early study carried out by scientists at Stanford University in California also fond that people who were exposed to pesticides were more than two times as likely to develop Parkinson's disease as those who were not exposed to the chemicals. The results were reported in 2000 at the annual meeting of the American Academy of Neurobiology in San Diego, California.

However, Lorene Nelson, lead author of the study and colleagues found exposure to pesticides in the home environment was linked to the highest risk of developing Parkinson’s disease. People who used pesticides in their gardens were not found to be at greater risk for the disease.

The current study, supported by a grant from the Michael J. Fox Foundation and Kinetic Foundation, was unable to reveal the association between a particular pesticide and risk of Parkinson’s disease. How the duration, frequency and level of exposure to pesticides affect the risk of the disease remains unknown.

Parkinson's disease is a progressive neurological disorder that results from degeneration of neurons in a region of the brain that controls movement. It remains unclear why pesticides may increase the risk of Parkinson's disease. But scientists say toxic pesticides may target and kill cells in some parts of the brain. Such damage to nerve cells leads to signs of Parkinson's disease.