Monday May 9 2011
Children's leukaemia risk was not raised by nearby nuclear plants
“Nuclear power plants have been cleared of causing childhood cancers by experts from the UK government's advisory committee”, reports The Guardian. The newspaper says the experts have found that children living near nuclear power plants in Britain are no more likely to develop leukaemia than children living elsewhere.
The findings, from a major report on nuclear power and childhood leukaemia, also suggest that there may be other reasons for “clusters” of childhood leukaemia, such as infections. The report was requested by the Department of Health and devolved authorities in response to decisions to build new nuclear reactors in the UK.
Who produced the report?
These news reports are based on a report published by the Committee on Medical Aspects of Radiation in the Environment (COMARE). COMARE was set up in 1985 to assess and advise the government on the effects of natural and man-made radiation.
The Chairman of COMARE is Professor A. T. Elliot who is a professor of Clinical Physics & Consultant Clinical Physicist from the University of Glasgow. The present committee includes 15 members, who are experts in fields such as childhood cancer, radiology, public health and the environment from UK hospitals, universities and other organisations. A number of former members also contributed to the production of the report. The contributors to this report have declared any conflicts of interest, such as any positions or investments that they hold within the nuclear industry.
What did the report look at?
The current report was COMARE’s 14th major report, and it focused on the incidence of childhood leukaemia in the vicinity of nuclear power plants. The report was produced in response to a 2009 government request for COMARE to review recent research publications on the subject.
The COMARE 2005 report had concluded, based on the evidence available up to 1993, that “there is no evidence from this very large study that living within 25 km of a nuclear generating site in Britain is associated with an increased risk of childhood cancer”.
The current report aimed to update information on the incidence of childhood leukaemia in the vicinity of nuclear power plants in Great Britain. It sought to compare this with information from other countries (including a recent study from Germany which found an association), and determine whether the statement from 2005 needed to be revised. The report considers Great Britain only (England, Scotland and Wales), as there are no nuclear power plants in Northern Ireland.
What evidence did the report contain?
The report comprised of various components:
- it reviewed epidemiological studies from Great Britain and other countries concerning childhood leukaemia and nuclear power plants (NPPs) or other nuclear installations; this included a review of a recent case-control study from Germany on this issue called the KiKK study
- it presented a new analysis looking at the geographical incidence (new cases) of childhood leukaemia in children living near nuclear power plants (NPPs) in Great Britain, based on cancer registry data
- it compared the pathology (biology and cellular characteristics) of cases of childhood leukaemia and non-Hodgkins lymphoma that occurred near to NPPs with matched cases that were not living near NPPs, to see if they differed
- it described cancer registries from several countries in Europe, as well as the nuclear reactors present in several European countries, radioactive discharges from these reactors, and consequent radiation exposure of the general public in these countries
- it considered factors not considered in previous COMARE reports, which may account for differences in the results of studies looking at childhood leukaemia in the vicinity of NPPs in different countries.
What were the basic findings?
The report looked at a large number of studies, and reported extensively on its findings. Some of its main findings are described below.
The report concluded that previous geographical studies from Great Britain showed no significantly increased risk of childhood cancer within 25km of an NPP, and no significant trend for increased risk with increasing proximity to an NPP. An analysis of British data on leukaemia and Non-Hodgkin’s lymphoma also showed no increase in risk for children aged under five years who lived within 5km of an NPP between 1969 and 2004. Studies from other countries also showed no general increase in childhood leukaemia near to NPPs.
The report’s analysis of new data for Great Britain found no statistically significant evidence of an association between leukaemia risk in children aged under five years old, and proximity to NPPs.
What kind of evidence did it look at?
The epidemiological studies that were consulted tend to be of two types:
- case-control studies: these compare factors such as NPP proximity in children with and without the disease to assess whether the level of risk of the condition is associated with each factor
- geographical studies: these compared the standardised incidence rate of disease in small geographical areas with differing characteristics (e.g. distance from an NPP)
These two study types have their own strengths and weaknesses. One weakness of both study types includes the possibility that factors other than the factor of interest (distance from an NPP) are affecting the results, a phenomenon known as confounding.
One particular difficulty encountered when researching this area is the fact that childhood leukaemia is a rare disease, affecting about 500 children aged 0 to 14 in the UK every year. This means that relatively few cases are available for study. For example, the KiKK study from Germany included only 37 cases of leukaemia in children aged under five, and despite more than 35 years of data collection this new report found only 20 cases in UK children aged under five living within 5km of the NPP.
Despite these limitations, the report concluded that the geographical analysis for Great Britain suggested that the risk for childhood leukaemia associated with proximity to an NPP is extremely small, if not actually zero.
Why did the German research find a link?
The report also looked at potential reasons why the KiKK case-control study from Germany found evidence of an increased risk of leukaemia in children aged under five who lived within 5km of an NPP between 1980 and 2003. The report says that excess radiation exposures to the general public living near to NPPs in Germany are likely to be a factor of 1,000–100,000 times lower than those from background radiation and are unlikely to be the cause of this raised risk.
The findings of the KiKK study were found to be heavily influenced by earlier time periods (1980 to 1993), with less association seen in the later period (1996 to 2003). Also, excluding cases around one NPP in northern Germany (the Krümmel plant) for the periods 1991 to 1995 and 1996 to 2003, the evidence for increased risk within 5km of the remaining plants is weak. A study looking at the cluster around the Krümmel plant found that it could not be explained by routine radioactive discharges.
In addition, the leukaemia risk findings for 1980 to 1990 differ between the KiKK case-control study and geographical studies. Suggested reasons for this were differences in distance measurements used, and how controls were selected for the KiKK study. The report says that further investigation is required to understand this as the data for this specific time period has influenced the findings of the KiKK report.
The report also says that studies from Britain and Germany suggest that the risk of leukaemia in areas considered for nuclear sites but where the plants were never built is similar to that in areas with an active nuclear site. This suggests that risks may be associated with factors relating to the location selected for a nuclear plant rather than a risk from the plant itself. For example, the socioeconomic and lifestyle factors of individuals living near NPPs may differ from those who live in cities and less remote areas.
What did the report conclude?
Based on the evidence identified and analysed in the review, COMARE concluded that it saw no reason to change its previous advice to the government – i.e. that there is no evidence to support the view that there is an increased risk of childhood leukaemia and other cancers in the vicinity of NPPs in Great Britain.
What recommendations did the report make?
The report made five recommendations:
- The government should keep a “watching brief” in the area of childhood cancer and leukaemia and NPPs. This was because although COMARE found no reason to change its previous advice, they acknowledged that it is “almost impossible to come to a final conclusion on questions determined by epidemiological evidence alone”. Also, circumstances relevant to risk may change over time (e.g. changes in operating practices, and new ways to monitor and analyse data).
- There should be continued research into leukaemia and cancer, both related and unrelated to radiation, in order to help determine the causes of childhood leukaemia.
- There should be no reduction in the maintenance of effective surveillance relating to NPPs, particularly regarding the environment and health of the population. They say that this will be particularly important if the new nuclear build programme goes ahead.
- The monitoring of radioactive carbon-14 discharges in gas and liquid form should remain a legal requirement for existing NPPs and new NPPs in the UK. This is because the report found that carbon-14 is a significant contributor to the radiation doses received by the public from discharges from NPPs.
- UK-wide cancer registration resources, such as the UK National Registry of Childhood Tumours, should continue to be specifically supported because they allow comprehensive epidemiological analyses of childhood and adult cancers.