Cell phone risks remain fuzzy

Do cell phones cause brain tumors?

The World Health Organization (WHO) hoped a $30 million study, involving 50 scientists in 13 countries, would provide an answer. Its "Interphone" study reported its final results in May and, sadly, we remain none the wiser.

"An increased risk of brain cancer is not established, but it's important to note that we can't establish absence of risk, either," says study leader Elisabeth Cardis of the Center for Research in Environmental Epidemiology in Barcelona, Spain. So why can't Cardis be more conclusive?

In a retrospective study, between 2000 and 2006 her team enlisted 6,400 people with brain tumors and a similar number of healthy people. They were then quizzed on how much they had used a cell phone. The idea was that if the phones boost the risk of tumors, there would have been more phone use in the tumor group compared with the general population, and less phone use in the healthy group. But the opposite was found (International Journal of Epidemiology).

Good news for cell phone addicts? Not so fast. When the team got back in touch with healthy people who had declined to take part in the study, they discovered that these people were less likely to be regular phone users (defined as making more than one call a week for more than six months) than the healthy people who took part. This means that the benefit that cell phones seemed to offer could just be down to an over-representation of people who were both healthy and regular users. It also means that any detrimental effects might have been masked.

Despite this bias toward positive results, when the researchers compared the 10 percent of cell phone users who spent the most time on their phones with non-users and infrequent users (defined as less than one call per week), this level of use did appear to increase the risk of gliomas by 40 percent and meningiomas by 15 percent.

These increases became even more pronounced when only tumors on the same side of the head as sufferers said they held their cell phones were counted. Frustratingly, the extent to which even these findings can be trusted is unknown, due to another problem.

Because the study was retrospective, the researchers relied on participants' memories, going back up to 10 years, of how much they had used their handsets before being enrolled, and on which side of the head. Yet people who are ill are subject to "recall bias" -- a tendency to exaggerate memories of potential risk factors.

What should we make of all this? Cardis advises caution: "It may not be an unreasonable course of action to limit exposure through the use of text messages, hands-free devices and speaker phones." But Mike Repacholi, who helped set up the study while at the WHO, is more positive: "The study says use of cell phones isn't associated with tumors."

Further studies are underway, but don't hold the line: The prospective Cosmos study hasn't begun yet, and aims to follow users for 20 to 30 years.

 

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