Study supports radiation exposure link to circulatory disease
MedWire News: Moderate radiation doses are associated with an increased risk for both heart disease and stroke, shows research published in the British Medical Journal.
The findings come from a large study of atomic bomb survivors by Yukiko Shimizu and colleagues from the Radiation Effects Research Foundation in Nagasaki, Japan.
They indicate that stroke and heart disease together account for around one third as many radiation associated excess deaths as do cancers among atomic bomb survivors.
The study included 86,611 survivors with estimated radiation doses, a large proportion of whom were within 2.5 km of the hypocenters at the time of the bombings and still resided in Hiroshima or Nagasaki in 1950. The remaining participants were an age- and gender-matched sample of people who were living 2.5–10.0 km from the hypocenters and sustained small to negligible radiation doses.
Shimizu and team report that 9622 participants died of stroke, 8463 of heart disease, and 969 of other circulatory diseases between 1950 and 2003.
Their analysis showed that each 1-Gy increment in radiation exposure conferred an estimated 11% excess relative risk for death from all circulatory diseases (p<0.001) – representing about 210 excess cases of circulatory disease death.
For heart disease, the corresponding excess relative risk was 14% (p<0.001). The association was linear, indicating an excess risk even at low doses. However, the dose–response effect when restricted to the range 0.0–0.5 Gy was not significant.
For stroke, the estimated relative risk per Gy was 9% (p=0.02), and the association was non-linear, suggesting relatively little risk at lower doses. This was confirmed by low-dose range analyses, indicating a 3% excess relative risk per Gy for the range 0–1 Gy and -7% for the range 0.0–0.5 Gy. No threshold was found.
Further analysis indicated that the associations held true after taking into account lifestyle, sociodemographic, or other health factors or misdiagnosis.
“Given the widespread use of multiple computed tomography scans and other relatively high dose diagnostic medical procedures, as well as radiotherapy that exposes the heart, the implications are substantial in so far as effects occur at doses under 1 Gy,” write the authors.
They conclude: “This study provides the strongest evidence available to date that radiation may increase the rates of stroke and heart disease at moderate dose levels (mainly 0.5–2.0 Gy), but robust confirmatory evidence is needed.
“Although our results below 0.5 Gy are not statistically significant, the additional cases occurring with further follow-up time should provide more precise estimates of the risk at low doses.”
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By Caroline Price