WASHINGTONThe latest effort to establish whether exposure to radiation during nuclear weapons tests caused leukemia in some military personnel has left the issue largely unresolved. The study by the Institute of Medicine (IOM) found a 14% increase in leukemia deaths among test participants, compared with a control group, but the increase was not significant. The increase was significant, however, for soldiers exposed to land-based testing.
The study also showed a significantly increased risk of death from nasal cancer, prostate cancer, and external causes, such as motor vehicle accidents, for the servicemen at the nuclear tests. The findings on nasal and prostate cancer were not expected based on other studies of the health effects of radiation exposure, the report said.
The study, The Five Series Study: Mortality of Military Participants in the US Nuclear Weapons Tests, is one of the largest of its kind. It was funded by the Department of Defense and carried out by four members of the IOM staff.
Between 1945 and 1963, more than 200,000 US soldiers, sailors, airmen, and marines took part in atmospheric nuclear weapons tests. Concern about their potential cancer risks accelerated in 1976 after a veteran claimed his leukemia resulted from exposure to radiation during a 1957 test.
The new IOM study, which supersedes one published in 1985, examined the causes and rates of death among nearly 70,000 servicemen present during at least one of five groups of atmospheric nuclear tests in the Nevada desert and South Pacific during the 1950s. These data were compared with deaths among nearly 65,000 servicemen who were on active duty at the same time, but who were not present at any nuclear tests. The reports findings are based on more than 5 million person-years of mortality follow-up.
Insufficient Dose Data
A major problem for the researchers was that dose data for test participants were insufficient and judged inappropriate for epidemiologic analysis. As a result, the study assessed the hazards associated with test participation, irrespective of dose.
The key findings of the study were that, overall, participants and referents had similar risks of death and death from cancer, and that the 14% higher risk of leukemia deaths among participants could be a chance finding.
The number of estimated excess deaths from leukemia among nuclear test participants was 25. Only a study cohort four times the size of the one available would have been likely to identify the observed leukemia risk as statistically significant, the report said.
The researchers found a statistically significant increased risk of leukemia deaths among servicemen at the Nevada site tests, compared with land-based members of the control group. And the estimated relative risk for leukemia mortality was higher among those servicemen exposed to radiation on land than those exposed at sea. There was no articulated a priori basis to have predicted such a finding, the report said.
However, participants in the South Pacific tests had an observed but not significant lower risk of dying of leukemia than members of the control group who were stationed at sea. There was also a statistically significant increased risk of death from all causes among the South Pacific test participants, compared with the sea-based controls.
The researchers found that among leukemia subtypes, the highest relative risk existed with lymphoid leukemia, excluding chronic lymphoid leukemia.
The leukemia findings are consistent with other studies and do not resolve the debate over whether either participation in general or the radiation dose in particular is associated with leukemia mortality, the report said. It added that the set of leukemia findings presented here is broadly consistent with a radiogenic cause, but is not conclusive.