Increased prenatal exposure to methylmercury does not affect the risk of Parkinson's disease

This study aimed to determine whether prenatal methylmercury (MeHg) exposure is a risk factor for Parkinson's disease (PD). A total of 172 clinically confirmed PD cases and 1018 controls matched by vital status, sex and age were included. The cases were ascertained in 1995 or were diagnosed during 19952005 in the Faroe Islands where the prevalence of PD is twice as high as elsewhere in northern Europe. Because the main single source of increased MeHg exposure in the Faroes is whale meat, retrospective exposure assessment was possible using detailed whaling records, rules of whale meat distribution and census lists. The share for each resident was calculated from the total amount of whale meat landed divided by the number of residents in the district entitled to a share. Utilizing the calculated share per resident at the mother's residence prior to the date of parturition, maternal body burden profiles were calculated as the average hair Hg concentration during the whole pregnancy, during the third trimester, and at the beginning of the third trimester. The exposures were compared between cases and controls using Mantel-Haenszel odds ratios (ORs), chi(2) and logistic regressions. All analytical methods gave ORs close to 1.0, none of them approaching statistical significance. The upper confidence limit was clearly below 2.0 in all analyses. No significant association between PD and prenatal MeHg exposure was found in this study, thus providing no support for prenatal MeHg exposure as an important risk factor that might explain the doubling of PD prevalence in this population.