Alzheimer's disease and prior therapeutic radiation exposure: a case-control study

Few risk factors have been identified for dementing illness to date. To evaluate prior therapeutic radiation exposure as a potential risk factor for Alzheimer's disease, we carried out a retrospective case-control study using the Rochester Epidemiology Resource. Cases were all incident cases of AD from 1960 through 1974 (N = 392) identified in an ongoing study of the condition in this community. One age- and sex-matched control for each case was selected from all registrations for care during the year of onset in the case. There were 86 cases and 89 controls with prior radiation exposure, and the variable used to describe exposure was absorbed dose. Most of the exposure was small doses: 11 individuals received greater than 1,000 centigray (3 cases, 8 controls). Using the logistic regression methods of Breslow and Day, the estimated odds ratio for any prior therapeutic radiation exposure was 0.95 (95% CI, 0.66 to 1.37). When the exposure variable was limited to head exposure only, the odds ratio was 0.65 (95% CI, 0.32 to 1.31). It is unlikely that the risk associated with therapeutic radiation in the development of Alzheimer's disease is greater than 1.4.