Excess Relative Risk of Mortality from Diseases of the Circulation System after Irradiation. Report 2. Combined Data Analysis for Nuclear Workers

In the second part of the review on estimates of excess relative risks (ERR) per 1 Gy/Sv for mortality from diseases of the circulatory system (ICD-9: 390–459; ICD-10: I00–I99) after irradiation, a combined analysis and meta-analysis was carried out for nuclear industry workers of various countries. The completeness of the sample at the end of 2021 appeared to be exhaustive. The combined analysis of the data consisted in assessing the average for the sample after eliminating outliers from it; ERR per 1 Gy/Sv was 0.20 (95% CI: 0.11; 0.30). The meta-analysis was performed on the full sample, without removing outliers. Some heterogeneity was identified, so a Random effect model was used for the meta-analysis, and the ERR per 1 Gy/Sv was 0.11 (95% CI: 0.01; 0.22). The mean value of ERR per 1 Gy/Sv obtained here only for nuclear industry workers, as well as the result of the meta-analysis, did not differ much from the data of M.P. Little and co-workers (2010–2016) for heterogeneous samples from different populations. At the same time, the data for ‘Mayak’ PA on mortality from circulatory pathologies in general, and not for their individual types, indicate lower risks for external exposure (Azizova TV et al., 2018): ERR per 1 Gy/Sv was 0.04 (95% CI: –0.00; 0.09). All listed risks from the point of view of classical epidemiology, when using the common Monson scale for relative risks (RR), should be considered either ignorable (RR = = 1.0–1.2) or weak (RR = 1.2–1.5). An estimation of the absolute risk of mortality from circulatory pathologies for a hypothetical group of 100,000 nuclear workers who each accumulated a dose of 1 Gy, based on data on the baseline mortality of men from these pathologies for the United States, showed an increase of 1400 deaths over 20 years of employment. However, recalculation for the real average dose accumulated by workers in different countries (31.1 mSv; Koterov A.N. et al., 2021) revealed an insignificant increase in mortality at 0.6% of the baseline level, which risk cannot be taken into account for such multifactorial pathologies. The results obtained in the second part of the presented study: a) reinforce the conclusion made in Report 1 about the advisability of adhering to the dose threshold of 0.5 Gy for circulatory pathologies mortality established by UNSCEAR, ICRP, NCRP, BEIR, etc.; b) they indicate very low, negligible risks of mortality from circulatory pathologies attributed to the radiation factor for nuclear industry workers in recent decades and for most of those even in the previous period; c) they show that for the real activity and health protection of the majority of workers in the nuclear industry, the determination/calculation of the radiation risks of mortality from circulatory pathologies is of an exclusively theoretical nature. These conclusions are important, among other things, for expert advices on establishing the causality of occupational pathologies in nuclear industry workers.