Polychlorinated biphenyls in prospectively collected serum and Parkinson's disease risk

Evidence suggests possible Parkinson's disease (PD)-relevant neural effects of exposure to polychlorinated biphenyls. Limited epidemiological evidence suggests that polychlorinated biphenyl exposure may increase PD risk, but no studies have involved biomarkers of polychlorinated biphenyl exposure before PD onset. We examined the prospective association between serum polychlorinated biphenyls and PD. We conducted a nested case-control study within the Finnish Mobile Clinic Health Examination Survey with serum samples collected during 1968-1972 and analyzed in 2005-2007 for polychlorinated biphenyls. Incident PD cases were identified through the Social Insurance Institution's registry and were confirmed by medical record review (n = 101). Controls (n = 349) were matched on age, sex, municipality, and vital status. We used logistic regression to estimate adjusted odds ratios. There was no evidence of increasing risk of PD with increasing polychlorinated biphenyl exposure in adjusted analyses. Instead, there was a trend toward lower odds of PD with increasing serum polychlorinated biphenyl concentrations, which was most pronounced for the sum of all measured polychlorinated biphenyl congeners and the sum of dioxin-like congeners. Compared with that of those in the lowest quintile, the odds ratio of PD among those in the highest quintile of total polychlorinated biphenyls was 0.29 (95% confidence interval, 0.12-0.70; P trend = .02) and for dioxin-like congeners was 0.34 (95% confidence interval, 0.13-0.90; P trend = .05). These results do not support an increased risk of PD from polychlorinated biphenyl exposure and instead suggest a possible protective effect of polychlorinated biphenyl exposure.