Use of medical radiotherapy has increased markedly in recent decades. Whether the consequence includes an increased risk of cardiovascular disease remains to be determined. The purpose of this study was to examine the association between radiation exposure and the incidence of stroke among Japanese atomic bomb survivors.
A prospective follow-up study.
Setting and participants
Radiation exposure from the atomic bombing was assessed in 9515 subjects (34.8% men) with 24-year follow-up from 1980. Subjects were free of prevalent stroke when follow-up began.
Stroke events and the underlying cause of death were reviewed to confirm the first-ever stroke. Subtypes (ischaemic and haemorrhagic events) were categorised based on established criteria according to the definitions of typical/atypical stroke symptoms.
Overall mean radiation dose (±SD) in units of gray (Gy) was 0.38±0.58 (range: 0–3.5). During the study period, 235 haemorrhagic and 607 ischaemic events were identified. For men, after adjusting for age and concomitant risk factors, the risk of haemorrhagic stroke rose consistently from 11.6 to 29.1 per 10 000 person-years as doses increased from <0.05 to ≥2 Gy (p=0.009). Incidence also rose within the dose range <1 Gy (p=0.004) with no dose threshold. In women, the risk of haemorrhagic stroke rose with increasing radiation exposure but not until doses reached a threshold of 1.3 Gy (95% CI 0.5 to 2.3). Among women, for doses <1.3 Gy, differences in stroke risk were modest (13.5 per 10 000 person-years), while it increased to 20.3 per 10 000 person-years for doses that ranged from 1.3 to <2.2 Gy and to 48.6 per 10 000 person-years for doses that were higher (p=0.002). In both sexes, dose was unrelated to ischaemic stroke.
While the risk of haemorrhagic stroke increases with rising radiation exposure for both sexes, effects in women are less apparent until doses exceed a threshold at 1.3 Gy.
Use of medical radiotherapy has increased in recent decades.
Whether the consequence includes an increased risk of cardiovascular disease is unknown.
Our purpose was to examine the association between radiation exposure and the incidence of stroke among atomic bomb survivors in Japan.
Risk of haemorrhagic stroke increased with rising radiation exposure for both sexes, although effects in women were less apparent until doses exceeded a threshold at 1.3 Gy.
Radiation exposure was unrelated to ischaemic stroke.
Strengths and limitations of this study
This report provides information on the incidence of stroke using data from clinical examinations and mortality records following a structured research protocol.
Measurement of radiation exposure adheres to a precise system of quantification.
While best attempts were made to properly classify strokes outcomes, diagnostic uncertainties persist.