Exposure to pesticides is associated with a significantly increased risk of developing Parkinson's disease and other degenerative parkinsonian syndromes, a large European multicenter study shows.
Moreover, the risk of Parkinson's increased, depending on the level of pesticide exposure. That suggests a cause-and-effect relationship. “Many previous studies have found such an association, but few have established an exposure-response relationship,” investigators wrote in their report, which was published online in May in Occupational and Environmental Medicine.
Having ever been knocked unconscious and first-degree family history of Parkinson's disease also were each significantly associated with increased Parkinson's risk, wrote Dr. Finlay Dick of the department of environmental and occupational medicine at Aberdeen (Scotland) University and associates.
The researchers enrolled 959 patients with parkinsonism, including 767 with Parkinson's disease, from centers in Italy, Malta, Romania, Scotland, and Sweden, along with 1,989 age- and gender-matched controls from clinics or the community at each site. Subjects completed a questionnaire about lifetime occupational and hobby exposure to solvents, pesticides, iron, copper, and manganese.
Adjusted logistic regression analysis showed that the strongest association was among patients with a first-degree family history of Parkinson's disease (odds ratio 4.85).
Significant dose-response associations were seen between the development of Parkinson's disease/parkinsonism and exposure to pesticides (odds ratio 1.13 for low exposure vs. no exposure; OR 1.41 for high vs. no exposure) and ever having been knocked unconscious (OR 1.35 for once vs. never; OR 2.53 for more than once vs. never). The researchers stressed that the study did not make clear whether head injuries occurred before disease onset, adding that the association might be due to recall bias or an increased risk of falls in Parkinson disease. “Head injury has previously been linked to an increased risk of Parkinson's disease, but the results have been inconsistent,” they noted (Occup. Environ. Med. 2007 May 30 [Epub doi:10.1136/oem.2006.027003]).
Patients taking, for more than 1 year, medication for depression (OR 1.92) or anxiety (OR 1.95), or sleeping pills (OR 1.33) also were at significantly elevated risk for developing Parkinson's disease and parkinsonism. “One explanation for this finding is that depression has been associated with an increased risk of Parkinson's disease later in life. The use of psychotropic medication may simply reflect the well recognized psychiatric effects of Parkinson's disease,” the researchers wrote.