Ischaemic heart disease incidence and mortality in an extended cohort of Mayak workers first employed in 1948-1982

Objective: Incidence and mortality from ischaemic heart disease (IHD) was studied in an extended cohort of 22,377 workers first employed at the Mayak Production Association during 1948-82 and followed up to the end of 2008. Methods: Relative risks and excess relative risks per unit dose (ERR/Gy) were calculated based on the maximum likelihood using Epicure software (Hirosoft International Corporation, Seattle, WA). Dose estimates used in analyses were provided by an updated "Mayak Worker Dosimetry System-2008". Results: A significant increasing linear trend in IHD incidence with total dose from external g-rays was observed after having adjusted for non-radiation factors and dose from internal radiation {ERR/Gy=0.10 [95% confidence interval (CI): 0.04 to 0.17]}. The pure quadratic model provided a better fit of the data than did the linear one. No significant association of IHD mortality with total dose from external g-rays after having adjusted for non-radiation factors and dose from internal alpha radiation was observed in the study cohort [ERR/Gy=0.06 (95% CI:<0 to 0.15)]. A significant increasing linear trend was observed in IHD mortality with total absorbed dose from internal alpha radiation to the liver after having adjusted for non-radiation factors and dose from external g-rays in both the whole cohort [ERR/Gy=0.21 (95% CI: 0.01 to 0.58)] and the subcohort of workers exposed at alpha dose,1.00Gy [ERR/Gy=1.08 (95% CI: 0.34 to 2.15)]. No association of IHD incidence with total dose from internal alpha radiation to the liver was found in the whole cohort after having adjusted for non-radiation factors and external gamma dose [ERR/Gy=0.02 (95% CI: not available to 0.10)]. Statistically significant dose effect was revealed in the subcohort of workers exposed to internal alpha radiation at dose to the liver,1.00Gy [ERR/Gy=0.44 (95% CI: 0.09 to 0.85)]. Conclusion: This study provides strong evidence of IHD incidence and mortality association with external g-ray exposure and some evidence of IHD incidence and mortality association with internal alpha-radiation exposure. Advances in knowledge: It is the first time the validity of internal radiation dose estimates has been shown to affect the risk of IHD incidence.