Study links low dose radiation and Down's syndrome

BMJ 1995; 310 doi: (Published 29 April 1995) Cite this as: BMJ 1995;310:1088

A new study has provided evidence of a link between fallout from the testing of nuclear weapons and Down's syndrome. It found that women in the Fylde area of Lancashire had higher rates of births of children with Down's syndrome during periods when fallout was particularly heavy. The report also noted that a fire at the nearby Windscale (now Sellafield) nuclear power station in 1957 was followed by a surge in cases of Down's syndrome.

The research is by Dr John Bound, a former paediatrician at the Victoria Hospital, Blackpool; Brian Francis, of the Centre for Applied Statistics, Lancaster; and Dr Peter Harvey, pathologist at the Royal Lancaster Infirmary. The results appear in the latest issue of the Journal of Epidemiology and Community Health (1995;49:164-70).

The authors of the report analysed 167 cases of Down's syndrome among 12015 total births in the region between 1957 and 1991. Other sources of radiation, such as x rays, were also taken into account. Women were divided into two age groups, over and under 35, to take account of the increased likelihood of women over 35 giving birth to a child with the syndrome.

The incidence of the syndrome was compared with statistics provided by the National Radiological Protection Board, which give estimates of the whole body radiation doses that the average Briton received each year from fallout from nuclear tests. Figures for radiation of testes in adults, which should match that of ovaries, were also compared. The researchers found that the two peaks of fallout, in 1958 and 1962-4, also coincided with peaks in the rate of cases of Down's syndrome, particularly in the older age group. At the time of the 1958 peak younger women were largely unaffected, but among women over 35 the incidence rocketed from 67 to 431 cases per 10000 births. At the time of the 1962-4 peak the incidence among young women doubled from 7 to 14 cases per 10000 births, while that among older women rose from 64 to 153 per 10000.

Dr Bound summarises: “Our findings are another piece of evidence that low dose radiation is an aetiological factor in Down's syndrome. It seems that the total dose you've had in your life is much more important than any individual dose. The greater susceptibility of older women suggests that these low doses may be the straw that broke the camel's back.”

In fact radiation related to the nuclear industry is only a small part of the total dose of radiation that we absorb. Background radiation, whether from cosmic rays or ionising materials in the earth, accounts for 90% of the radiation we receive. Of the remaining 10%, about nine tenths comes from medical treatments and scans.

The women of the Fylde region were exposed to increasing amounts of diagnostic medical radiation throughout 1957-91, but this had little effect. The average dose went up by 14% each year at the Victoria Hospital—except for a steady period between 1957 and 1962—but this seemed to have had little effect on the rates of births of children with Down's syndrome. “We did have a progressive radiologist at the Victoria, who implemented all the recommendations about dose reduction and shielding that came out at that time,” says Dr Bound.

Down's syndrome was first diagnosed in 1866, when natural radiation was the only kind of radiation to which the population was exposed. Although our exposure has increased by only about 10% since then, the recorded incidence of Down's syndrome has risen steadily through this century.

Dr Bound and his colleagues largely exonerate Sellafield (and Windscale), noting that the Fylde has a similar incidence of Down's syndrome to the national average. However, they suggest that a reactor fire at the plant in 1957 could have led to greater ground deposits of radioactive material during the 1958 peak. There was also a non-significant rise after the Chernobyl cloud passed by Fylde, although Dr Bound adds that Chernobyl generated only about a quarter as much radiation in the area as the nuclear tests of the 1950s and 1960s. Greater correlation between that nuclear accident and birth defects was found by researchers in Lothian and in Berlin.—OWEN DYER, freelance journalist, London

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