In order to understand what the long-term radiation-related effects might potentially be for residents in Japan today after the current nuclear accident, researchers report in Disaster Medicine and Public Health Preparedness that a study of the long-term health of the atomic explosions of Nagasaki and Hiroshima could provide some insight.

The review article in this American Medical Association (AMA) journal examines risk estimates and explains what we have learned from the survivors 63 years later. The AMA informs that this article is open access.

The authors note:

“Approximately 40% of the A-bomb survivors, but about 80% of those exposed before age 20 years, are alive today.”

The original directive to examine the medical and biological effects of the atomic bomb on human beings was approved by US President Harry Truman. The ABCC (Atomic Bomb Casualty Commission) was created in 1947 – in 1975 it became the RERF (Radiation Effects Research Foundation). The RERF aim was to continue researching the health effects of the atomic bomb survivors and their offspring. They received financial and scientific help from both the US and Japanese governments.

In 1955 the Life Span Study was initiated. It tracked mortality and cancer incidence among 120,000 survivors of the two atomic bombs – they were compared to control subjects. The authors also examined several other studies with small cohorts.

The authors wrote:

“ABCC/RERF scientists have used primarily two types of risk calculations to describe the magnitude of health effect associated with radiation exposure in epidemiological studies. The excess absolute risk rate (EAR) refers to the difference in the rate of occurrence of disease between an exposed population and a comparable population with no exposure. The relative risk is the ratio of the occurrence rate in the exposed population to that in the nonexposed population.

(The excess relative risk – ERR – is) “a measure of the strength of the effect of exposure and may have biological significance, whereas the EAR is a measure of the absolute size of the effect, which may be of public health or clinical significance.”

The investigators report that several years after the bombings the risk of leukemia rose, followed by a gradual increased risk of solid cancers some time later.

They added:

“Because the A-bomb survivors received whole-body exposures from the penetrating radiation, excess cancer risks (ERR and EAR) have been estimated for a large number of organ sites. Dose responses are significant for cancers of the oral cavity, esophagus, stomach, colon, liver, lung, nonmelanocytic skin, female breast, ovary, urinary bladder, brain/central nervous system, and thyroid.”

The researchers also found that life spans were reduced, there were neurological effects, and also psychological ones.

The authors informed:

“Median (midpoint) loss of life was about two months for those with doses less than 1 Gy (gray = dose of radiation) and 2.6 years for those with doses greater than 1 Gy. It was estimated that at 1 Gy, the proportion of total life lost was roughly 60 percent from solid cancer, 30 percent from diseases other than cancer, and 10 percent from leukemia.

The ERR for people exposed to the bombs at a younger age is higher than those exposed at an older age. The risk is about twice as high after exposure at age 10 than at age 40. For all ages at exposure, the ERR declines over time (with increasing attained age). Contrarily, the EAR increases rapidly with age, with no apparent indication of abating, suggesting that the radiation-related excess risk may persist throughout one’s lifetime, and this trend is seen for most of the cancer sites.

(Conclusion) The lessons learned from establishing the cohorts and the pioneering analyses by ABCC and RERF scientists should serve as a legacy for future generations who experience occupational, medical, or environmental radiation exposures.”

Nuclear Preparedness Special Issue – All Content Open Access
Disaster Medicine and Public Health Preparedness March 2011, Volume 5, Issue Supplement 1

Written by Christian Nordqvist