Exposure to Pesticides Linked to Risk for Parkinson's Disease

May 30, 2007 — Exposure to pesticides is associated with risk for Parkinson's disease, according to the results of a case-control study reported in the May 30 Online First issue of Occupational and Environmental Medicine.

"It seems likely that Parkinson's disease is not a single disease but a number of phenotypically similar illnesses," write F.D. Dick, from the University of Aberdeen in Scotland and colleagues from the Geoparkinson study group. "A variable range of genetic and environmental interactions may produce these conditions and it may be that any individual risk factor will only affect susceptible subjects. The discovery that 1-methyl-4-phenyl tetrahydropyridine, a contaminant of a synthetic opiate, can cause parkinsonism through its neurotoxic metabolite, 1-methyl-4-phenylpyridinium, stimulated interest in environmental chemical exposures as risk factors for Parkinson's disease."

This case-control study included 959 prevalent cases of parkinsonism (767 with Parkinson's disease) and 1989 controls in Scotland, Italy, Sweden, Romania, and Malta. Cases were defined using the UK Parkinson's Disease Society Brain Bank criteria; those with drug-induced or vascular parkinsonism or dementia were excluded.

Interviewers administered a questionnaire about lifetime occupational and hobby exposure to solvents, pesticides, iron, copper, and manganese. Using a job-exposure matrix modified by subjective exposure modeling, lifetime and average annual exposures were estimated blind to disease status. Multiple logistic regression analysis adjusted for age, sex, country, tobacco use, head trauma resulting in loss of consciousness, and family history of Parkinson's disease.

Adjusted logistic regression analyses revealed significantly increased odds ratios (ORs) for Parkinson's disease/parkinsonism. There was an exposure-response relationship for pesticides (low vs no exposure: OR, 1.13; 95% confidence interval [CI], 0.82 - 1.57; high vs no exposure: OR, 1.41; 95% CI, 1.06 - 1.88) and ever knocked unconscious (once vs never: OR, 1.35; 95% CI, 1.09 - 1.68; more than once vs never: OR, 2.53; 95% CI, 1.78 - 3.59).

Hypnotic, anxiolytic, or antidepressant drug use for more than 1 year and a family history of Parkinson's disease were also associated with significantly increased ORs, whereas tobacco use was protective (OR, 0.50; 95% CI, 0.42 - 0.60).

Analyses excluding subjects with forms of parkinsonism other than Parkinson's disease yielded similar results.

"The association of pesticide exposure with Parkinson's disease suggests a causative role," the authors conclude. "Repeated traumatic loss of consciousness is associated with increased risk."

Study limitations include possible recall bias, possible differences across the 5 centers in methods of case ascertainment (neurologist review vs note-based classification), lack of data on specific pesticide exposure, and probable underestimate of pesticide exposure because of the seasonal nature of pesticide use.

"This study has provided important evidence of the increased risk of Parkinson's disease in relation to exposure to pesticides," the authors conclude. "The exposure–response relationship suggests that pesticide exposure may be a causative and potentially modifiable risk factor."

The European Union as part of the Fifth Framework programme supported this study.

Occup Environ Med. Published online May 30, 2007.

Source: http://www.medscape.com/viewarticle/557465?src=mp