Concerns have been raised in New Zealand and abroad about whether exposure by pregnant women to electromagnetic radiation from cellphone towers may increase their child’s risk of developing early childhood cancers such as leukaemia and brain tumours.
Previous studies into such effects have failed to offer a sufficiently final response to the question. However, a study published this week in the British Medical Journal appears to have laid such concerns to rest.
In the largest such study of its kind, researchers analysed data from 1,397 children under the age of four who had cancer, compared with 5,588 children as the control group. They looked at where the children’s mothers had lived during pregnancy, how near the locations were to cellphone masts, and the power output of those masts.
The study found no link between early childhood cancers and cellphone mast exposure during pregnancy. However, its authors did caution that the link being looked at was specifically between such exposure and early childhood cancers – they draw no conclusions about any other possible health effects.
See below for an analysis of the research commissioned by the UK Science Media Centre and conducted by UK research group Bazian.
The research follows the publication last month of the Interphone study on mobile phone handsets and tumours. The audio of an SMC briefing on that research and an SMC infographic on mobile phone radiation can be accessed here. Feel free to use any of this material in your reports.
The UK and NZ SMCs rounded up comments from experts:
The paper can be accessed in the SMC Resource Library.
Dr David Black, Occupational & Environmental Medicine Specialist and member of the Royal Society of New Zealand, comments:
“This is a welcome and helpful study which should help to clarify an issue which still seems to cause some public debate. It is also pleasing to see that it doesn’t end in “more research is needed”, because it’s clearly not.
“The idea that the tiny amounts of radio-frequency energy which are absorbed by pregnant women from mobile phone base stations, let alone that which might reach their unborn children, could cause any biologically change is a very unlikely hypothesis. However the driver for studies like this is not serious scientific hypotheses, it is public concern with is engendered by poor scientific literacy and is fed by inordinate attention being paid to meaningless collections of case reports packaged as ecological studies.
“It is time to regard this matter as settled and apply scarce public health research funding to real issues where there is at least prima facie evidence of an actual problem.”
Martin Gledhill, Senior Advisor (Science) at the National Radiation Laboratory, comments:
“This new study supports the widely held view that exposures which comply with current exposure limits – and especially exposures at the levels typically found in the urban and rural environment – do not cause cancer. Wth its emphasis on determining realistic exposure estimates, this study is a great improvement over the small number of previous studies on cellsites and cancer whose weaknesses did not permit any conclusions to be drawn. It can be viewed alongside recent studies on radio and TV transmitters which, using realistic exposure estimates, found no increased risk of childhood leukemia associated with exposure to TV and radio signals.
“Of course, this one study does not answer all questions about a possible relationship between exposure to radiofrequency fields (such as those from cellsites) and cancer, but its findings are consistent with the conclusion reached in recent research reviews that such a relationship is unlikely.”
Dr Eileen Rubery, former head of the Public Health Prevention Department at the Department of Health (UK), comments:
“This is a carefully done study by a highly reputable group of environmental researchers. The size of the sample is large and the approach appropriate.
“It is reassuring that no adverse affects have been found and this fits with the anticipated and known biological effects from such sites and so is consistent with the physiology and biology.”
Professor Malcolm Sperrin, Director of Medical Physics at the Royal Berkshire Hospital (UK), comments:
“This study seems exemplary in its approach. The findings are well concluded and the methodology is thorough. The findings are generally in support of both the current understanding of tissue interactions and also in support of the work done by other similar research groups. The data is complex and requires some interpretation but the abstract and conclusions are well considered and easy to follow.”
Science Media Centre UK appraisal:
Contact email: firstname.lastname@example.org
Appraisal by: Bazian
Appraisal date: 22 June 2010
Citation: Elliot P et al. Mobile phone base stations and early childhood cancers: case-control study. BMJ 2010;340:c3077
The study was carried out by researchers from the School of Public Health at Imperial College London.
The study was funded by the UK Mobile Telecommunications Health Research (MTHR) Programme, an independent body set up to fund research into the possible health effects of mobile telecommunications. The MTHR is jointly funded by the UK Department of Health and the mobile telecommunications industry.
This was a case control study looking at whether there was a relationship between exposure to mobile phone masts in pregnancy and early childhood cancers in the offspring.
The researchers analysed data from 1,397 children aged up to four years old who had cancer (cases) – 73% of cases recorded in Great Britain in national cancer registries for 1999 to 2001. They were compared with 5,588 children without cancer (controls) who were matched to the cases for gender and date of birth. They determined where the children’s mothers had lived at the time of their birth, and how near it was to mobile phone masts. They then compared the cases and controls to see if their mothers had lived at different distances from mobile phone masts, or whether they were exposed to different levels of power output from these masts.
The four national mobile phone operators (Vodafone, O2, Orange, and T-Mobile) provided information on all 81,781 mobile phone antennae in use from 1 January 1996 to 31 December 2001. They excluded 4,891 low power antennae covering limited areas (called microcells, accounting for 6% of the antennae). The researchers had full data on 66,790 (87%) of the 76,890 remaining antennae. Where data was missing, it was estimated using the data that the researchers had on other antennae, or was assigned the average (median) value for the company.
The researchers assumed that during their pregnancy the mother had lived at the address/postcode registered at birth. For each child, they calculated the distance of this address from the nearest base station, the total power output from all base stations within 700m, and power density for base stations within 1400m. They based calculations of power density in a given area on measurements taken in a survey of a rural area, and an urban area. These calculations used complex mathematical models, which were checked against data obtained from other surveys and measurements. The model appeared to perform better in predicting power density in rural areas than in urban areas. Pregnancies were assumed to last nine months, and exposure over the nine months prior to birth was estimated for each child.
They researchers looked at the relationship between mobile phone mast exposure in the womb and all childhood cancers, and also with specific cancers (brain and central nervous system cancers, leukaemia, and non-Hodgkin’s lymphomas). They took into account factors that could affect results, including socioeconomic deprivation, population density, and population mixing (migration into the area in the previous year). Data on these factors was obtained from the 2001 census for the small area containing the birth address (census output area).
Results of the study:
Of the 1,397 cancer cases, 527 were leukaemia and non-Hodgkin’s lymphoma (38%), and 251 brain and central nervous system cancers (18%). Cases and controls were similar in terms of social and demographic characteristics.
On average, the children who had cancer had birth addresses 1,107 metres from the nearest base station, and controls had birth addresses 1,073 metres from the nearest base station. The researchers found no significant difference between children with early childhood cancer and controls in distance of birth address from nearest base station. They also found no significant difference between children with cancer and controls in total power output or modelled power density exposure from the mobile phone antennae at their birth addresses during their gestation (time in the womb).
The researchers also found no differences in distance from nearest base station, total power output, or modelled power density between healthy controls and children with specific cancer types (either leukaemia and non-Hodgkin’s lymphoma, or brain and central nervous system cancer).
The researchers concluded that they found “no association between risk of childhood cancers and mobile phone base station exposures during pregnancy”. They say that their results “should help to place any future reports of cancer clusters near mobile phone base stations in a wider public health context”.
Strengths and limitations:
This study appears well conducted. Its strengths include:
* Analysis of data from children born across Great Britain and inclusion of a high proportion (73%) of all registered early childhood cancer cases in Great Britain for the period assessed (1999-2001). This reduces the possibility that the area or children selected may not be representative of most cases.
* The use of three different methods to assess exposure to mobile phone base stations during pregnancy, all of which showed no association with childhood cancer.
Its limitations include:
* It only assessed the effects of exposure during pregnancy on early childhood cancers (up to age four). Longer term effects or effects of later exposure during infancy and childhood were not assessed.
* Researchers did not measure individual exposure, and therefore they had to use surrogate measures of exposure. Although measuring individual exposure would have been ideal, doing so on a large cohort of pregnant women would be unlikely to be feasible.
* The researchers had to make certain assumptions in order to carry out their analyses. For example, they assumed that all pregnancies lasted nine months and calculated exposures based on registered birth address. In some cases, pregnancies may have been shorter or slightly longer than nine months, and mothers may have moved house or have spent significant amounts of time in other areas (e.g. for work). The accuracy of the assumptions may affect the results.
* The researchers were not able to assess radiofrequency exposure from other sources, such as low power mobile phone antennae, maternal use of mobile phones in pregnancy, radio or TV transmitters, or cordless phone base stations.
* Although the researchers took into account factors that could affect results, these or other factors may still be having an effect.