On August 6, 1945, the U.S. dropped an atom bomb on Hiroshima. Nagasaki was bombed three days later.
In the 1950 Japanese national census nearly 280,000 persons claimed that they were exposed to radiation. Initially, the Atomic Bomb Casualty Commission and from 1975, Radiation Effects Research Foundation (RERF), carried out several studies on the survivors.
Research programmes
The research programmes covered Life Span Study (LSS), Adult Health Study, study of the Children of Atomic-bomb Survivors (F{-1}) and the evaluation of the lifetime health experience of a specially exposed population, namely those in utero at the time of the bombings.
Other areas covered included immunology, radiation biology, molecular epidemiology, cytogenetics, statistics and A-bomb dosimetry.
RERF researchers and other scientists studied the interaction with radiation and smoking.
Radiation increased the risk of lung cancer among the survivors. Among 105,404 subjects of the LSS, researchers identified 1803 primary lung cancer cases for the period 1958-1999.
They used individual smoking history information and the latest radiation dose estimates to investigate the combined effects of radiation and smoking on lung cancer rates.
Lung cancer risks
Relative to never-smokers, lung cancer risks increased with the amount and duration of smoking and decreased with time since quitting smoking at any level of radiation exposure ( Radiation Research, 174, 2010 ).
The excess risk increased rapidly with smoking intensity up to about 10 cigarettes per day, but additive or sub-additive for heavy smokers smoking a pack or more per day, with little indication of any radiation-associated excess risk
The authors concluded that the joint effect of smoking and radiation on lung cancer in the LSS is dependent on smoking intensity and is best described by the generalized interaction model rather than a simple additive or multiplicative models
Fatty liver predicts ischemic heart disease or heart disease due to reduced blood supply to the heart.
Fatty liver predictors
The researchers at RERF observed the incidence and predictors of fatty liver by examining 1635 survivors of Nagasaki A-bomb every two years through 2007 (mean follow up for 11.6 y) by abdominal ultrasonography.
The subjects were without fatty liver at base line (November 1990 through 1992). The researchers diagnosed 323 new fatty liver cases.
The average incidence was 19.9 cases in 1000 person years peaking in the sixth decade of life ( Hypertension Research April 2010).
After controlling for age, sex, and smoking and drinking habits, obesity, hypertriglyceridemia (large levels of tryglicerides) and hypertension were predictive of fatty liver.
All variables included
When all variables are included, obesity, hypertriglyceridemia and hypertension remained predictive.
Scientists have not observed genetic effects in the children of A-bomb survivors.
To evaluate the genetic effects of A-bomb radiation, RERF researchers examined mutations at specific loci in the chromosomes of exposed families (father-mother-offspring, mostly uni-parental exposures) and control families. The mutation rates observed were not statistically significant.
That radiation exposure causes thyroid cancer is an established fact.
But we do not know the radiation effects on papillary micro carcinoma (PMC) of the thyroid, a common sub-clinical thyroid malignancy.
RERF researchers identified PMCs in a subset of 7659 subjects after reviewing their pathology and evaluating the histological features of the tumors.
Papillary thyroid cancer
From 1958 to 1995, they detected 458 PMCs among 313 study subjects; most of them exhibited pathologic features of papillary thyroid cancers.
A significant radiation-dose response was found for the prevalence of PMCs with the excess risk observed primarily among women.
Exposure to low-to-moderate doses of ionizing radiation appears to increase the risk of thyroid PMCs, even when exposure occurs during adulthood ( Cancer , 2010).
Raja Ramanna Fellow with the Department of Atomic Energy
( ksparth@yahoo.co.uk )
