An analysis of brain tumor incidence in Scandinavian countries from the mid 1970s to the early 2000s found no substantial change in brain tumor rates in adults 5 to 10 years after cell phone usage rose sharply. However, the researchers cautioned that there could be reasons other than the absence of a link to explain these findings, and suggested longer follow up studies were needed.
The study was the work of Dr Isabelle Deltour of the Institute of Cancer Epidemiology, Danish Cancer Society, in Copenhagen, and colleagues, and a paper on it was published in the Advance.
Some studies have suggested cell phone use is a risk factor for brain tumors, but there is no evidence that explains a biological basis for this risk, said a JNCI press release.
Cell phone use in Denmark, Finland, Norway, and Sweden rose sharply in the mid 1990s. The researchers worked on the assumption that, after a period of development of say 5 years, if there weas a link between cell phone use and brain tumors, one might expect time trends in brain tumor incidence after around 1998 to reflect a similar pattern.
Using data from national cancer registries, and statistical tools called “joinpoint regression models”, they analyzed the annual incidence rates of glioma and meningioma from 1974 to 2003 in Denmark, Finland, Norway, and Sweden.
The results showed:
* From 1974 to 2003, in a population of 16 million adults, 59, 984 men and women aged 20 to 79 years were diagnosed with brain tumors.
* Incidence rates over the 30 years either remained stable, went down, or continued a gradual increase that began before people started using cell phones.
* Among men, the incidence rate of glioma increased by 0.5 per cent per year (95 per cent confidence interval [CI] ranged from 0.2 to 0.8 per cent).
* Among women, the incidence rate of glioma increased by 0.2 per cent per year (95 per cent confidence interval [CI] ranged from 0.1 to 0.5 per cent).
* Among men, the incidence rate of meningioma increased by 0.8 per cent per year (95 per cent confidence interval [CI] ranged from 0.4 to 1.3 per cent).
* Among women, after the early 1990s, the incidence rate of meningioma increased by 3.8 per cent per year (95 per cent confidence interval [CI] ranged from 3.2 to 4.4 per cent).
* No change in incidence trends from 1998 to 2003, when potential links with cell phone usage would be visible after an induction period of 5 to 10 years.
The authors expressed caution about interpreting these findings, and wrote they could reflect reasons other than the absence of a link between cell phone usage and brain tumor risk.
For example it could be that it takes much longer than 5 to 10 years for the effect of cell phone use to show up as a brain tumor risk.
Another explanation for these findings could be that the percentage of the population affected by such a risk is too small to be noticed in this type of analysis, or in a similar vein, the increased risk is restricted to subgroups of brain tumors or cell phone users.
Deltour explained these points to the press:
“We found no correlation in this study,” she said.
“That means perhaps that there is no risk in talking on a mobile phone, but it can also mean that it takes longer than five or ten years to develop cancer of the brain,” she explained, adding that, “it may also mean that a possible increased risk is very small, or perhaps only for some specific groups of people and therefore cannot be measured in a study covering the entire population.”
She and her colleagues suggested that:
“Because of the high prevalence of mobile phone exposure in this population and worldwide, longer follow-up of time trends in brain tumor incidence rates are warranted.”