Abstract 5133: Lifetime Risk of Stroke in Atomic-bomb Survivors-Adult Health Study in Hiroshima and Nagasaki, Japan
Background: It is suggested that Atomic-bomb radiation may cause increase in stroke mortality. The objective of this study was to estimate the radiation effect on lifetime risk (LTR) of stroke among Atomic-bomb survivors. Our hypothesis is that even low-dose radiation may cause stroke incidence in different mechanism of high-dose irradiation.
Methods: We evaluated radiation effect on stroke incidence by dose and age at time of bombing (ATB) groups: < 0.005 Gy (n=2607), 0.005– 0.5 Gy (n=2051), 0.5–1.0 Gy (n=939), 1.0+Gy (n=824) and < 10 y.o. (younger) vs. ≥ 10 y.o. (older) ATB. Adult Health Study (AHS) subjects were Atomic-bomb survivors and unexposed controls. Participants have been followed biennially by RERF since 1958. Eligible subjects were alive and stroke-free at baseline age (55–56 y.o.) and had corresponding blood pressure data available. Stroke events were all reviewed by WHO MONICA methods using health exam and death certificate information. Cumulative incidence and LTR analyses accounted for the competing risk of non-stroke death with consideration of blood pressure levels.
Results: Median follow-up for the 7487 subjects was 16.1 years (range: 1 day to 44.3 years), where 3788 subjects had died, 868 had a documented first-ever stroke event (356 male, 512 female). These stroke events were classified as hemorrhagic (n=231), thromboembolic (n=542), and unspecified (n=95). A minority of subjects (11%) was <10 y.o. ATB, and dose was unknown in 1066 subjects. There was no significant difference among 4 dose-groups in cumulative incidence rates of any stroke as well as hemorrhagic or thromboembolic stroke. However, there was a significant difference when we considered age ATB within dose groups (p=0.0003). Ten-years risk estimates for any stroke were 3.0% in 0 – 0.005 Gy, 2.0% in 0.005– 0.5 Gy, 5.0% in 0.5–1.0 Gy, 11.1% in 1.0+ Gy (p<0.0001), even within subtypes (hemorrhagic stroke; p=0.053, thromboembolic stroke; p=0.0034).
Conclusion: Our results suggest that Atomic-bomb radiation in young subjects increases risk of stroke. Continued observation is needed due to the limited follow-up time in AHS subjects <10 y.o. ATB. This is the first report on the LTR of stroke incidence supporting the long-term radiation related increase in stroke mortality.