Written by Catharine Paddock Phd
In recent years we have seen studies yielding conflicting evidence on links between mobile phone use and risk of developing brain cancer as a result of radiation exposure. Now an update of a large and long-running nationwide study in Denmark concludes there is little evidence of a causal link between cell phone use and brain cancer and other types of central nervous system tumors. Experts say this is reassuring news but urge we continue to keep an eye on the situation.
Researchers from the Institute of Cancer Epidemiology at the Danish Cancer Society in Copenhagen looked at national health and mobile phone records in Denmark, and compared cancer rates between long-term mobile phone users and the rest. They published their findings online in the 20 October issue of the BMJ.
The health data covered all Danes aged 30 and over who were born in Denmark after 1925, and the researchers divided this population into two groups: those who became mobile phone subscribers before 1995 (this came to 358,403 subscribers, totalling 3.8 million person years of usage) and the rest (about 3.2 million Danes). They then cross-referenced this data with entries in the complete Danish Cancer Register to calculate the risk of tumors of the central nervous system.
The results showed that:
- 10,729 cases of tumours of the central nervous system occurred between 1990 and 2007 in the whole of the cohort.
- 846 of the tumors occurred in people thought to have been using mobile phones since before 1995.
- There was essentially no increased risk of such a tumor in the mobile phone group compared to the rest.
- There was little difference in the results between men and women, between long-term and shorter term mobile phone users, and for different types of tumor.
“There was no indication of dose-response relation either by years since first subscription for a mobile phone or by anatomical location of the tumour – that is, in regions of the brain closest to where the handset is usually held to the head,” write the authors, who conclude that: “In this update of a large nationwide cohort study of mobile phone use, there were no increased risks of tumours of the central nervous system, providing little evidence for a causal association.”
In an accompanying editorial, Anders Ah and Maria Feychting, both professors at the Institute of Environmental Medicine, Karolinska Institutet in Stockholm, Sweden, write that while these findings are reassuring, we should continue to monitor health registers and prospective cohorts.
Other experts appear to agree.
Hazel Nunn, head of evidence and health information at Cancer Research UK, said that this study was the “strongest evidence yet”, and “minimized many of the problems of previous research in this area, but she also urges continued monitoring:
“Even longer term follow up of cancer risk in mobile phone users is still needed, as are studies of effects of mobile phone use in children.” Dr Jonathan Samet, a professor of preventive medicine at the University of Southern California’s Keck School of Medicine, in Los Angeles, led the World Health Organization panel that ruled radiation from cell phones may “possibly” cause cancer. He says while this study does not show a link, it does not establish safety, that is the absence of risk.”This is a useful addition to the literature, and we need more studies of high quality,” he told WebMD.