Mesothelioma and Lung Cancer
Epidemiologic Studies
What are some of the statistically significant epidemiologic studies that demonstrate risk decrements (hormesis) as predicted by the adaptive responses to low-dose radiation of the DNA damage-control biosystem? 4 For several decades increased longevity and decreased cancer mortality have been reported in populations exposed to high background radiation. Established radiation protection authorities consider such observations to be spurious or inconclusive because of unreliable public health data or undetermined confounding factors such as pollution of air, water and food, smoking, income, education, medical care, population density, and other socioeconomic variables. Recently, however, several epidemiologic statistically significant controlled studies have demonstrated that exposure to low or intermediate levels of radiation are associated with positive health effects.
Dr. Zbigniew Jaworowski, past chairman of UNSCEAR, in his current review of hormesis cites recent data showing hormetic effects in humans from the former Soviet Union.5 After radiation exposure from a thermal explosion in 1957, 7852 persons living in 22 villages in the Eastern Urals were divided into three exposure groups averaging 49.6 cGy, 12.0 cGy, and 4.0 cGy and followed for 30 years. Tumor-related mortality was 28%, 39%, and 27% lower in the 49.6 cGy, 12.00 cGy, and 4.0 cGy groups, respectively, than in the nonirradiated control population in the same region. In the 49.6 cGy and 12.0 cGy groups the difference from the controls was statistically significant. Epidemiologic studies showing beneficial effects of low doses of radiation in atomic bomb survivors and other populations were reviewed by Sohei Kondo, Professor of Radiation Biology, Atomic Energy Research Institute, Kinki University, Osaka, Japan.6
Included are the apparently beneficial effects of low doses of external gamma rays on the life span of radium-dial painters and the significantly lower mortality from cancers at all sites of residents of Misasa, an urban area with radon spas, than residents of the suburbs of Misasa;. [INLINE] These beneficial effects are consistent with the findings of B. L. Cohen, Professor of Physics, University of Pittsburgh, that relate the incidence of lung cancer to radon exposure in nearly 90% of the population of the United States.7 The 1601 counties selected for adequate permanence of residence provide extremely high-power statistical analysis.
After applying the BEIR IV 8 correction for variations in smoking frequency, the study shows a very strong tendency for lung cancer mortality to decrease with increasing mean radon level in homes, in sharp contrast to the BEIR IV theoretical increased mortality derived by linear no threshold extrapolation of effects in uranium miners exposed to very high radon concentrations. The discrepancy between theoretical and measured slopes is 20 standard deviations. Rigorous statistical analysis of 54 socioeconomic, seven physical, and multiple geographic variables as possible confounding factors, both single and in combination, demonstrates no significant decrease in the discrepancy. The multiple independent requirements that a possible unknown confounding factor must meet, make its existence highly improbable.
A reasonable explanation is that stimulated biological mechanisms more than compensate for the radiation "insult" and are protective against cancer in a low-dose, low-dose-rate range. The thirteen-year U.S. Nuclear Shipyard Workers study of the health effects of low-dose radiation was performed by the Johns Hopkins Department of Epidemiology, School of Public Health and Hygiene, reported to the Department of Energy in 1991 9 and reported in UNSCEAR 1994.4 Professor Arthur C. Upton, who concurrently chaired the NAS BEIR V Committee on "Health Effects of Exposure to Low Levels of Ionizing Radiation," 10 chaired the Technical Advisory Panel that advised on the research and reviewed results. The results of this study contradict the conclusions of the BEIR V report 10 that small amounts of radiation have risk - the LNT hypothesis. From the database of almost 700,000 shipyard workers, including about 108,000 nuclear workers, three closely matched study groups were selected, consisting of 28,542 nuclear workers with working lifetime doses 5 mSv (many received doses well in excess of 50 mSv), 10,462 nuclear workers with doses <5 mSv and 33,352 non-nuclear workers. Deaths in each of the groups were classified as due to: all causes, leukemia, lymphatic and hematopoietic cancers, mesothelioma cancer, and lung cancer. The results demonstrated a statistically significant decrease in the standardized mortality ratio for the two groups of nuclear workers for 'death from all causes' compared with the non-nuclear workers. For the 5 mSv group of nuclear workers, the highly significant risk decrement to 0.76, 16 standard deviations below 1.00, of the standard mortality ratio for death from all causes is inconsistent with the LNT hypothesis and does not appear to be explainable by the healthy worker effect 4.
The non-nuclear workers and the nuclear workers were similarly selected for employment, were afforded the same health care thereafter, and performed the identical type of work, except for exposure to 60 Co gamma radiation, with a similar median age of entry into employment of about 34 years. This provides evidence with extremely high statistical power that low levels of ionizing radiation are associated with risk decrements. Nevertheless, Professor Arthur C. Upton and others consider the three-country low-dose radiation and cancer study of Cardis, et al11,12, to be the best occupational study of nuclear workers.
This study concluded, "There was no evidence of an association between radiation dose and mortality from all causes or from all cancers. Mortality from leukemia, excluding chronic, lymphocytic leukemia (CLL) ...was significantly associated with cumulative external radiation dose (one-sided P value = 0.046: 119 deaths)." The statistical methods used state, "As there was no reason to suspect that exposure to radiation would be associated with a decrease in risk of any specific type of cancer, one-sided tests are presented throughout." The authors' analysis of the 119 deaths from all leukemias except CLL excluded 86 deaths in dose categories 1.3.4, and 6 in which there were fewer deaths than expected. Trend analysis of the remaining 33 deaths in dose categories 2, 5, and 7 for estimated P=0.046 was obtained "using computer simulations based on 5000 samples, rather than the normal approximation."11