Five months after the World Health Organisation classified radiofrequency electromagnetic fields as only “possibly carcinogenic to humans (Group 2B),” the findings of a study published in the British Medical Journal (BMJ) suggest no risk of brain tumour from mobile phone use. There was no indication of “dose-response relation either by years or by anatomical location of the tumour”. It was found to be true even among those who used mobile phones for more than 10 years. The conclusion is in line with more than a dozen large studies that looked for a possible link, including the first cohort study involving more than 400,000 Danish phone subscribers. In the latest instance, the study covered those diagnosed with brain tumour between 1990 and 2007 among more than 350,000 mobile phone subscribers in Denmark. By using digitised subscriber data obtained from operators, the researchers avoided two important methodological shortcomings — that of relying on users’ ability to recall phone usage pattern and, two, selection bias.
But the study has certain limitations. The conclusion was not based on the actual use of mobile phones — the period of subscription was used as a surrogate for phone usage. The compounding limitation was the potential misclassification of exposure. Corporate subscriptions were excluded from the study, and the data on subscribers were available only till 1995. Hence all corporate subscribers and those who had a subscription post-1995 were labelled ‘non-users’. However, it will be difficult, if not impossible, to conduct proper case-controlled studies that are free from selection and recall biases. For various reasons, even the most robust study to find a link based on usage pattern over the last 10 years or more will not be able to arrive at a correct conclusion. For instance, older analog phones used more energy than the currently available digital versions. Moreover, the energy given off by all the latest phones is not the same, and it also varies according to the strength of the signal — more energy is emitted when the signal is poor. Studies looking at effects from long-term usage will have little relevance to children, whose use of mobile phones has grown dramatically in recent years. Therefore, the need to adopt a precautionary approach to the use of mobile phones, especially by children, becomes extremely important. This, despite the fact that developed countries have witnessed no sudden spurt in brain tumour incidence, and the radiowaves, unlike X-rays and gamma rays, are non-ionising in nature and do not have the energy to damage cellular DNA.