Indeed, of thirteen epidemiological studies published since 1999 on cellphone use for more than ten years, eight suggest a two- to threefold risk increase.

Just the same, it’s hard to publish convincing results from studies like these. For one thing, cellphones have only been popular for a decade or so, making it difficult to find enough subjects who’ve used them for long periods of time. Add to this the fact that brain tumours are rare, and it becomes almost impossible to produce data that show definitive statistics. Of the eight epidemiological studies that suggest a positive association, for instance, only three are large enough to be considered “statistically significant.”

One way to circumvent these problems and acquire enough reliable data is to pool results from multiple trials. This is the idea behind Interphone, the largest study of its kind to date, coordinated by the International Agency for Research on Cancer in Lyons, France. Led by Canadian scientist Elisabeth Cardis, the project has analyzed some 6,400 tumours in thirteen countries. Here, too, however, mystery abounds. While results from some of the individual countries have been published, the pooled results — scheduled for release in 2006 — have not; Cardis says, “The interpretation isn’t clear.” In the January/ February issue of Microwave News, editor Louis Slesin writes, “The code of silence about Interphone must end. Public health demands it.”

Early this year, Siegal Sadetzki, a scientist at the Chaim Sheba Medical Center in Israel, and a participant in the Interphone study, published her country’s arm of the findings. Their report suggests that heavy cellphone users have a 50 percent increased risk of developing parotid gland tumours near the side of the head against which they hold their phones. “Significant risk is shown, and we should take this into consideration, because this technology is really, really, really prevalent,” she says.

While Sadetzki advocates caution (noting “usually it takes a long time to develop solid cancers; ten years is really only the minimum”), others maintain that a two- or threefold increase actually does not represent a large overall risk. Malignant brain tumours are rare — about one in 14,000 North Americans is diagnosed with one each year — and even a doubling of the risk for individuals who use cellphones for a decade means only about one in 7,000 people. But what about those who use cellphones for thirty years, or kids who start using them when they’re eight? No one knows.

Clearly, epidemiological studies in which scientists monitor the health and cellphone habits of large groups of people over extended periods of time are required. Properly constructed, such studies would solve problems of memory loss, recall bias, and other research-related challenges.

If the debate over whether cellphones are harmful is controversial, how they might be is even more so. Because cellphone radiation can’t knock around electrons enough to cause dna damage or heat tissue, its biological effects are probably due to something heat independent or “non-thermal.” However, no one knows yet how the radiation could do this, and many dispute that it does. Of the approximately 400 laboratory studies that have investigated whether exposure to radio frequency radiation affects dna in cells and/or animals, only about half report any effects.

Leif Salford, chair of neurosurgery at Lund University in Sweden, has repeatedly shown that exposure to two hours of cellphone radiation opens the bloodbrain barrier and causes brain-cell damage in rats. Other studies have shown that radiation affects biological pathways important for metabolism and stress responses. But what does this have to do with cancer? Although cellphone radiation, unlike uranium or plutonium, may not be powerful enough to cause tumours directly, it might, as Jerry Phillips suggests, indirectly lead to cancer by preventing dna repair mechanisms from working properly, and by producing free radicals, highly reactive molecules that can interact with dna in cancer-causing ways.

It may also be that cellphones don’t seed new tumours, but instead promote or accelerate the growth of existing ones. In other words, cellphone radiation could be what is called a “tumour promoter,” which would require less energy than tumour initiation. (Also, as people are already being bombarded by dozens of known environmental carcinogens, something that helps cancers grow is potentially a big problem.) In the first study Phillips conducted for Motorola, he used a chemical to make a tiny tumour and then looked at how radio frequency fields influenced its growth. “It did appear that these fields could affect already initiated tumours,” he says. According to University of Massachusetts Amherst toxicologist Edward Calabrese, animals and cells respond differently and inconsistently to low-level toxic exposures, so varied findings are not surprising. At low levels, he says, the way a body reacts to exposures can be counterintuitive, just as in Phillips’ experiment, where low exposures appeared to cause more damage than higher ones.

Probing these issues requires funding, but outside of the Interphone study interest seems to be flagging. The US government, which didn’t participate in Interphone, has not announced any plans to fund epidemiological studies. The National Toxicology Program has provided $22 million (US) for a series of trials to be performed at the Illinois Institute of Technology, but these animal studies will investigate only whether healthy rats and mice exposed to cellphone radiation develop brain cancer — and they may not, if cellphones are only tumour promoters.

This is certainly not the first time a ubiquitous product has become a potential public health threat, and the big question is, how will it all play out? The cellphone industry could follow in the steps of Big Tobacco and continue to cast doubt on legitimate studies. Or it could adopt the science-minded approach of the automobile industry, which has responded to obvious public health dangers by engineering new technologies — the airbag, for instance — that minimize risk and attract the public’s support.

In this era of Hollywood celebrities weighing in on international affairs, perhaps a media luminary like Larry King will call for long-term epidemiological research on the effects of habitual cellphone use. Or maybe good soldier Daniel Shattuck will discover the truth and broadcast it broadly; maybe he’ll find a less hesitant doctor.