This year we observed the 70th anniversary of A-bombing of Hiroshima and Nagasaki. In the 1950 Japanese national census, nearly 280,000 persons stated that they “had been exposed” in the two cities. The Radiation Effects Research Foundation (RERF)selected about 94,000 people to to study the health effects of radiation.
One of the most notable among these projects is the study of the survivors’ children. Quite contrary to popular perception, this study recently revealed that the children born to exposed parents did not suffer from excess cancer mortality or non-cancer deaths (The Lancet Oncology, September 15, 2015).
Dr Eric J Grant and co workers from the RERF looked at the birth records to identify children conceived after the atomic bombings and born in Hiroshima and Nagasaki. They also collected data from city offices which entertained applications from pregnant women.
The study included 75,327 children of atomic bomb survivors in the two cities and unexposed controls, born between 1946 and 1984, and followed up to Dec 31, 2009. Researchers interviewed the parents directly or matched them to a master list of survivors to estimate the radiation exposure to their reproductive organs. This dose depended on distance of the individual from the hypocentre, shielding from such objects as buildings or hills and shielding from intervening tissues inside the body before radiation reached a particular organ.
The study covered 16,869 children with one or both parents within 2 km of the hypocentres. The researchers compared them with 18,450 children born to one or both parents resident in the city before and after the bombing but neither parent closer than 2.5 km to the hypocentres and 16,738 children who had both parents outside of the cities at the time of the bombing. Researchers matched the comparison groups by year of birth, sex, and city.
They cautioned that the study is still underpowered. Ninety per cent of the cohort is still alive. Further follow up will enhance the statistical power of the study.
What is the importance of the study? In an accompanying comment, David Brenner, Center for Radiological Research, Columbia University Medical Center, U.S. noted that in the first decade or so after the explosions, scientists focussed most of the concerns about long-term health on potential heritable genetic effects in subsequent generations.
They relied on Dr. Herman Mueller's 1927 study which showed that radiation could induce heritable genetic effects in fruit fly.
“Since the 1950s, however, understanding of the relative importance of genetic and somatic radiation related effects has completely reversed: genetic effects are now considered only a small contributor to the overall detriment to health after radiation exposure”, Brenner clarified. The conclusions from the latest study are consistent with the recent thinking on the topic.
. Long-term studies of the health impact of radiation on the progeny of A-bomb survivors have not shown any scientific evidence for heritable genetic effects.
Scientists assume that persons exposed to radiation may suffer from genetic effects as a matter of abundant caution as studies on fruit flies and mouse have shown that radiation can cause genetic effects. Though it is only an assumption, members of the public consider genetic effects of radiation as gospel truth — a wrong public perception prevails over a robust scientific fact.
While agreeing with Dr Brenner's view that “absence of evidence is not evidence of absence”, we need not lose sleep over the genetic effects of radiation as he rightly stated that “the risks must be small, otherwise they would have been observed in the children of survivors”.
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