On the low-dose-radiation exposure in the Techa River Cohort and mortality from circulatory diseases

Abstract

Among the conclusions of the article by Krestinina et al. (2013) was that chronic radiation exposure of the Techa River Cohort resulted in a radiation-related excess risk of death from diseases of the circulatory system (DCS) and from ischemic heart disease (IHD) in particular. At the same time, estimation of mortality risk from cerebrovascular disease did not reveal any statistically significant dependence on the dose. The relatively high mortality rates from cardiovascular disease in Russia compared to Western Europe were commented previously (Jargin 2013). Since the Soviet time, autopsy has remained obligatory for patients dying in hospitals; however, the attitude toward postmortem examinations has become in places less rigorous (Jargin 2008). Autopsies have been sometimes performed incompletely, without much insight. If a cause of death is not entirely clear, it is common practice to write into the death certificate the diagnosis of IHD, acute or chronic cardiac insufficiency, or a similar formulation. These facts are well known by pathologists with experience of autopsy in the former Soviet Union (SU). There is a tendency to overdiagnose cardiovascular diseases in unclear cases also in the people dying at home and not undergoing autopsy. This is likely to be one of the causes of the dramatic increase in cardiovascular mortality in the former SU since the 1970s, especially in men (Zatonski 2007; Zatonski and Bhala 2012). This is confirmed by Davydov and coworkers who wrote: ‘‘Increases and decreases in mortality [have been] related to cardiovascular diseases (CVD), particularly to ‘other forms of acute and chronic ischemia’ and ‘atherosclerotic heart disease,’ but not to myocardial infarction, the proportion of which in Russian CVD-related mortality is extremely low’’ (Davydov et al. 2007). The explanation for this controversy is evident for an inside observer: The diagnosis of myocardial infarction is usually based on clear clinical and/or morphological criteria, while IHD and cardiac insufficiency are often diagnosed postmortem without sufficient evidence. Analogous explanations pertain also to the fact that Krestinina et al. (2013) did not find any statistically significant dependence on the radiation dose of the mortality risk from cerebrovascular diseases: The latter usually have clear symptoms and are not habitually overdiagnosed. At least for the former SU, there is a tendency: The higher the quality of postmortem diagnostics, the lower the fraction of cardiovascular diseases among all causes of death. In this connection, the cause of the sixfold ethnic difference of the excess relative risk (ERR) per 100 mGy for all the DCS deaths (Krestinina et al. 2013) appears clear: the less thorough diagnostics in the ethnic minorities. Furthermore, according to the dose distribution in the cohort studied by Krestinina et al. (2013), only 2.7 % (n = 800) of the cohort members had dose estimates above 350 mGy, while 94.7 % of the cohort received individual doses below 150 mGy in the period 1950–2003. To the best of my knowledge, no association with cardiovascular or other diseases has ever been reliably proven for such a low dose level and rate (Jargin 2012). Doses above 0.5 Gy were reported to be associated with an elevated risk of both stroke and heart disease among the atomic bomb survivors, but the dose–response effect was not statistically significant when the calculation was limited to the dose range 0–0.5 Gy (Shimizu et al. 2010). For acute radiation doses above 1–2 Gy, a number of mechanisms were proposed, including damage to the endothelial cells in capillaries or larger blood vessels and the up-regulation of inflammatory S. V. Jargin (&) Peoples’ Friendship University of Russia (Moscow), Clementovski per 6-82, 115184 Moscow, Russia e-mail: sjargin@mail.ru