Occupational exposure to chronic ionizing radiation increases risk of Parkinson's disease incidence in Russian Mayak workers

Background: Patients receiving radiotherapy demonstrate cognitive deficits, impairment of neurogenesis and neurovascular damage developing as late side effects of radiation exposure to the head. In light of the increasing use of diagnostic radiological procedures, epidemiological data raise concerns about possible harmful effects of low-level radiation on the human brain. A series of studies of chronically exposed Russian nuclear workers have provided information on risks of cancer and non-cancer diseases. Methods: This study aimed to assess the risk of Parkinson's-disease (PD) incidence in a cohort of workers occupationally exposed to chronic radiation. The cohort comprised workers of a Russian nuclear production facility who were first employed in 1948-1982 and followed up until the end of 2013 (22 377 individuals; 25% female). Using the AMFIT module of EPICURE software, relative risk and excess relative risk per unit dose (ERR/Gy) were calculated based on maximum likelihood. Results: A linear association was found between PD incidence and cumulative gamma-dose after adjusting for sex and attained age [ERR/Gy = 1.02 (95% confidence interval, 0.59 to 1.63, p=5.44 x 10(-5))]. The ERR/Gy of external radiation for PD incidence was stable after adjusting for neutron dose (ERR/Gy = 1.03; 95% confidence interval: 0.59 to 1.67, p=6.86 x 10(-5)). The risk increased with increasing lag period and decreased notably after adjusting for body mass index, smoking and alcohol consumption. Additional adjustments for hypertension, gout, gastric ulcer, head injuries with loss of awareness and diabetes mellitus did not affect the risk estimate. Conclusions: This study is the first to suggest that PD is associated with prolonged occupational external gamma-ray exposure.