A large, long-term Scandinavian study has found no evidence that increased use of cell phones over a nine-year period led to more cases of brain cancer. The study tracked 16 million people in Finland, Denmark, Norway, and Sweden from 1974 to 2003.
The four Scandinavian countries have had a mobile phone network since 1981, two years before the service launched in the U.S.
Of the 16 million, 60,000 developed brain tumors, a rate that is not considered above average, according to an article in the Dec. 16 issue of the Journal of the National Cancer Institute. If cell phones were a significant cause of brain tumors, the national registries in the four countries should have shown an increased incidence.
The lack of any such signal in the registry data "is consistent with mobile phone use having no observable effect on brain tumor incidence in this period," the researchers wrote.
"If there was a connection we would have expected a sudden marked increase in the rates, especially among younger males, which were the first to start using mobile phones. And we don't see that," said Prof. Isabelle Deltour of the Institute of Cancer Epidemiology at the Danish Cancer Society in Copenhagen.
However, the researchers cautioned that there are several possible explanations for their findings: ? The period needed for cell phones to cause brain tumours was longer than the period studied; ? The increased risk in this population is too small to be observed; ? The increased risk is restricted to just certain cell phone users; ? There is no increased risk at all.
Other scientists not involved in the study also counseled caution.
"I don't think five to 10 years does cover it," David Carpenter, a professor of environmental health sciences and biomedical sciences at the University at Albany, State University of New York, told Scientific American. "Brain cancers are slow growing, so the idea that you would be able to detect something after five years would be surprising," he says. "Time will tell, but likely the biggest increase will be after 20 years."
Carpenter was among researchers from 14 countries endorsing a report issued in August that advocated greater caution in the use of cellular technology.
That report -- "Cell Phones and Brain Tumors: 15 Reasons for Concern" -- cautions that studies not financed or influenced by the telecommunications industry "consistently show there is a 'significant' risk of brain tumors from cell phone use."
Other studies, including a meta-analysis released in October, have suggested link but the authors of the Scandanavian study said that findings of increased brain cancer rates may simply reflect an increase in diagnoses from new imaging technologies.
Deltour and her colleagues cautioned that cell phone use could have risks for the heaviest users or for rarer tumor types. Additionally, if the induction period for tumors associated with cell phones is longer than 10 years, longer follow-up would be needed to detect it.
The researchers recommended continued study of population trends because of the enormous exposure to cell phones worldwide. The World Health Organization is expected to soon release results of a long-term study that reportedly shows a link between cell-phone use and brain cancer.
The study was funded by the Danish Strategic Research Council.
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