Moon, Mars and Minds: Evaluating Parkinson's disease mortality among U.S. radiation workers and veterans in the million person study of low-dose effects

Abstract

Background: Radiation is one of the most important stressors related to missions in space beyond Earth's orbit. Epidemiologic studies of exposed workers have reported elevated rates of Parkinson's disease. The importance of cognitive dysfunction related to low-dose rate radiation in humans is not defined. A meta-analysis was conducted of six cohorts in the Million Person Study (MPS) of low-dose health effects to learn whether there is consistent evidence that Parkinson's disease is associated with radiation dose to brain.

Materials and methods: The MPS evaluates all causes of death among U.S. radiation workers and veterans, including Parkinson's disease. Systematic and consistent methods are applied to study all categories of workers including medical radiation workers, industrial radiographers, nuclear power plant workers, atomic veterans, and Manhattan Projects workers at the Los Alamos National Laboratory and at Rocky Flats. Consistent methods for all cohorts are used to estimate organ-specific doses and to obtain vital status and cause of death.

Results: The meta-analysis include 6 cohorts within the MPS, consisting of 517,608 workers and 17,219,001 person-years of observation. The mean dose to brain ranged from 6.9 to 47.6 mGy and the maximum dose from 0.76 to 2.7 Gy. Five of the 6 cohorts revealed positive associations with Parkinson's disease. The overall summary estimate from the meta-analysis was statistically significant based on 1573 deaths due to Parkinson's disease. The summary excess relative risk at 100 mGy was 0.17 (95% CI: 0.05; 0.29).

Conclusions: Parkinson's disease was positively associated with radiation in the MPS cohorts indicating the need for careful evaluation as to causality in other studies, delineation of possible mechanisms, and assessing possible implications for space travel as well as radiation protection guidance for terrestrial workers.

Keywords: Million Person Study; Parkinson’s disease; Radiation epidemiology.

Figure 1

Forest plot and result of the summary ERR at 100 mGy brain dose from a Random Effects meta-analysis for Parkinson’s disease mortality based on 6 of the Million Person Study (MPS) epidemiologic studies. Excess relative risks at 100 mGy brain dose with 95% confidence intervals for Parkinson’s disease mortality are plotted on rows corresponding with each MPS study cohort. The summary estimate is displayed in the last row (and is indicated by the vertical dotted line). The total number of veterans in the A-Vets cohort was 114,270, however, the total number utilized in the dose response was 113,806, because of the exclusion of veterans with unknown doses. Abbreviations: NPP, nuclear power plant; IR, industrial radiographer; MRW, medical radiation workers; LANL, Los Alamos Nuclear Laboratory; RF, Rocky Flats; ERR, excess relative risk.