Incidence of dementia among atomic-bomb survivors--Radiation Effects Research Foundation Adult Health Study.

Radiotherapy has been reported to cause neuropsychological dysfunction. Here we examined whether exposure to atomic bomb radiation affected the incidence of dementia among 2286 atomic bomb survivors and controls - all members of the Adult Health Study cohort. Study subjects were non-demented and aged >or=60 years at baseline examination and had been exposed in 1945 at >or=13 years of age to a relatively low dose (<or=4 Gy), compared with total dose from radiotherapy. Dementia diagnoses were made during biennial health examinations with a two-phase procedure. DSM IV criteria were used for diagnosing dementia, NINCDS-ADRDA for Alzheimer disease, and NINDS-AIREN for vascular disease. To estimate the effect of radiation on the dementia incidence rate, we applied Poisson regression analysis. Incidence per 1000 person-years was 16.3 in the <5 mGy group, 17.0 in the 5-499 mGy group, and 15.2 in the >or=500 mGy group. Alzheimer disease was the predominant type of dementia in each dose category. After adjustment for potential risk factors, radiation exposure did not affect the incidence rate of either all dementia or any of its subtypes. No case of dementia had a history of therapeutic cranial irradiation. Although we found no relationship between radiation exposure and the development of dementia among atomic bomb survivors exposed at >or=13 years old in this longitudinal study, effects on increased risk of early death among atomic bomb survivors will be considered.