SAN DIEGO—Pesticide use and exposure in the home and garden may increase the risk of developing Parkinson's disease, according to a study of nearly 500 people newly diagnosed with the disease. "This study is the largest yet of newly diagnosed individuals with Parkinson's disease, and it is the first study to show a significant association between home pesticide use and the risk of developing Parkinson's disease," reported Lorene M. Nelson, PhD, at the 52nd Annual Meeting of the American Academy of Neurology.

Dr. Nelson and colleagues found that exposure to insecticides inside the home increased the risk of Parkinson's disease by 70%, exposure to garden herbicides increased the risk by 60%, and exposure to garden insecticides increased the risk by 50%. Adjustment for other possible risk factors, such as sex, age, education level, cigarette smoking, alcohol consumption, and family history of Parkinson's disease, did not change the risk estimates. Exposure to fungicides did not appear to increase the risk, said Dr. Nelson.

ESTIMATING PESTICIDE EXPOSURE

Enrolled in the study were 496 patients with recently diagnosed Parkinson's disease and 541 controls matched for age, sex, and respondent type (self versus proxy). During 1994 and 1995, the cohort was drawn from members of the northern California Kaiser Permanente Medical Care Program. The cohort was largely representative of the area population with respect to age, sex, race, and ethnicity but somewhat dissimilar in levels of education and income levels. Neither the very poor nor the very wealthy were represented, noted Dr. Nelson, who is Associate Professor of Epidemiology at Stanford University School of Medicine in California.

Estimates of cumulative pesticide exposure were based on information gathered during structured interviews and from questionnaires. Exposure was defined as direct handling or application of the pesticide more than five years before the diagnosis of Parkinson's disease. "Preclinical signs and symptoms could have altered patterns of use of pesticides in the period immediately prior to the person's diagnosis of Parkinson's disease," said Dr. Nelson. The researchers estimated first and last year of exposure, total cumulative years of exposure, number of days per year of exposure, and time since last exposure.

A CAUSAL RELATIONSHIP?

The researchers attempted to identify a dose response between the level of pesticide exposure and the risk of Parkinson's disease. "Obviously, we would like to see a dose-response relationship before we can conclude that pesticide exposure is likely to be a causal factor," said Dr. Nelson. She noted that a significant dose-response trend was seen for garden herbicide exposure: fewer than 30 days of exposure was associated with a 40% increased risk, while more than 30 days of exposure was associated with a 70% increased risk. However, no dose-response relationship was observed with respect to in-home and garden insecticide exposure.

Dr. Nelson acknowledged the public health implications of the research but cautioned that the findings are preliminary. Further investigations, she said, will need to include more detailed assessments of exposure (eg, pesticide types and brands, mode of exposure) and to address whether compliance with manufacturer's recommended precautions and instructions for pesticide use affect risk. "At this time, no specific guidelines regarding the complete avoidance of home pesticides can be given," Dr. Nelson said. However, she suggested, "those who use pesticides should follow manufacturers' guidelines to prevent skin and respiratory exposure."

—Kathryn Blair

Suggested Reading
Gorell JM, Johnson CC, Rybicki BA, et al. The risk of Parkinson's disease with exposure to pesticides, farming, well water, and rural living. Neurology. 1998; 50:1346-1350.
Le Couteur DG, McLean AJ, Taylor MC, et al. Pesticides and Parkinson's disease. Biomed Pharmacother. 1999;53:122-130.
Menegon A, Board PG, Blackburn AC, et al. Parkinson's disease, pesticides, and glutathione transferase polymorphisms. Lancet. 1998;352:1344-1346.

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