Childhood exposure to ionizing radiation to the head and riskof schizophrenia

While the association between exposure to ionizingradiation and cancer is well established, its associationwith schizophrenia is unclear. The aim of our study was toassess risk of schizophrenia after childhood exposure toionizing radiation to the head (mean dose: 1.5 Gy). Thestudy population included an exposed group of 10,834individuals irradiated during childhood for treatment oftinea capitis in the 1950s and two unexposed comparisongroups of 5392 siblings and 10,834 subjects derived fromthe National Population Registry individually matched tothe exposed group by age, sex (when possible), country ofbirth, and year of immigration to Israel. These groups werefollowed for a median 46 years for diagnosis of schizophreniaupdated to December 2002. The Cox proportionalhazards model stratified by matched sets was used tocompare the risk of schizophrenia between the groups.Based on 1,217,531 person-years of follow-up, 451 caseswere identified. No statistically significant association wasfound between radiation exposure and schizophrenia for thetotal group (hazard ratio per 1 Gy to the brain: 1.05, 95%confidence interval: 0.93-1.18) or within subgroups of sex,dose categories or latent period. When comparing asubgroup of subjects irradiated under 5 years of age withthe matched unexposed group, the estimated hazard ratioreached 1.18 (95% confidence interval: 0.96-1.44; P 0.1).The results of our analysis do not support an associationbetween exposure to ionizing radiation and risk ofschizophrenia. More research on possible effects of earlyexposure to ionizing radiation on schizophrenia specificallyand brain tissue in general is needed.