Excess Relative Risk of Mortality due to Diseases of Circulatory System after Radiation Exposure: Report 2. Combined Data Analysis for Nuclear Workers

In the second part of this review on estimates of excess relative risks (ERR) per 1 Gy/Sv of mortality due to diseases of the circulatory system (ICD-9: 390–459; ICD-10: I00–I99) after radiation exposure, a combined analysis and meta-analysis were performed for nuclear workers of various countries. The completeness of the sample at the end of 2021 appeared to be exhaustive. The combined analysis of the data involved assessment of the central tendencies for the sample after removal of outliers; ERR per 1 Gy/Sv was 0.20 (95% CI: 0.11; 0.30). Meta-analysis was performed on the full sample, without removing outliers. Heterogeneity warranted the use of the Random effect model for meta-analysis, and ERR per 1 Gy/Sv was 0.11 (95% CI: 0.01; 0.22). The mean value of ERR per 1 Gy/Sv obtained herewith for nuclear workers alone, as well as the results of the meta-analysis, did not differ much from the data of M.P. Little et al. (2010–2016) for heterogeneous samples from different contingents. At the same time, data for ‘Mayak’ PA on mortality due to circulatory pathologies altogether (rather than by their individual types), pointed toward lower risks for external exposure (Azizova et al., 2018): ERR per 1 Gy/Sv was 0.04 (95% CI: –0.00; 0.09). From the standpoint of classical epidemiology, when using the common Monson scale for relative risk (RR), all listed risks 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 due to circulatory pathologies for a hypothetical group of 100 000 nuclear workers each with a cumulative dose of 1 Gy, based on data on the baseline mortality in men due to these pathologies for the United States, showed an increase in the increment of 1400 deaths over 20 years of employment. However, recalculation for the true (actual) mean accumulated dose of workers from different countries (31.1 mSv) (Koterov et al., 2021, 2022) revealed a miniscule increase in mortality at 0.6% of the background level; the risk of this level cannot be taken into account for these multifactorial pathologies. The results obtained in this 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 mortality due to circulatory pathologies established by UNSCEAR, ICRP, NCRP, BEIR, etc.; (b) suggest very low, negligible risks of mortality due to circulatory pathologies attributed to the ionizing radiation factor for nuclear workers in recent decades and for most of those even in the early period; and (c) show that, for the actual activity and health protection of the majority of workers in the nuclear industry, the determination/calculation of the radiation risks of mortality due to circulatory pathologies is exclusively theoretical in nature. These conclusions are important, among other things, for the councils of experts that establish the causality of occupational pathologies in nuclear workers.