麻豆传媒

WITH hundreds of millions of people around the world using mobile phones, we ought by now to have some idea whether they pose a health risk. But ask experts in the field, and their contradictory views make an answer seem further away than ever.

Mobile phones have been blamed for causing everything from headaches to cancer. One study even suggested they might be beneficial, improving our reaction times. Just about the only thing that researchers agree on is that the hundreds of studies carried out so far are inconclusive. What they can鈥檛 agree on is what should be done next.

One leading industry scientist is calling for an end to research on health effects. In an interview in this magazine (see 鈥淚t鈥檚 good to talk鈥�), Mays Swicord, scientific adviser to Motorola Research in Florida, argues that the reason no health effects have been found is that there simply aren鈥檛 any. Doing yet more research is a waste of money, he believes.

At the World Health Organization, Michael Repacholi, head of mobile phone research, distances himself from this view, especially as the mobile phone industry has successfully cut the amount of research funding in the US. 鈥淲e don鈥檛 want to stop [ongoing] research,鈥� he told 麻豆传媒.

But Repacholi says that the WHO is unlikely to start any new research when its current review of mobile phone safety ends. 鈥淲e鈥檒l give it another three or four years,鈥� he says. 鈥淏ut at some stage we should turn to other areas of research that need our attention.鈥�

However, conclusive evidence is unlikely to emerge over that sort of timescale. A team at Imperial College London, backed by the UK government, is planning a long-term study that might just come up with convincing evidence one way or the other. But it has yet to begin work, and will not produce results for about 15 years.

Public fears about mobile phone safety were first raised by a series of headline-grabbing studies suggesting that mobile phone use was linked to disorders such as brain cancers (see 鈥淪eeds of controversy鈥�). But the studies were small, the results sometimes statistically insignificant, and none of them has held up to scrutiny or been reproduced.

To review the evidence and address the uncertainty over the risks, the British government commissioned a report from William Stewart, a former government chief scientist. In 2000, Stewart鈥檚 report concluded that there was little evidence of any biological effect from radio waves produced by phones, but acknowledged that there were still 鈥済aps in our knowledge鈥� that needed to be investigated. The report recommended, to many people鈥檚 surprise, a 鈥減recautionary approach鈥� towards the use of mobile phones, especially among children.

From this emerged the UK鈥檚 Mobile Telecommunications and Health Research Programme (MTHR), a series of government and industry-funded projects aimed at filling these gaps. A second report based on this work is due to be published this year. But it, too, is unlikely to provide the public with a definitive answer.

鈥淚鈥檓 not sure it was ever realistic to expect that,鈥� says David de Pomerai of the University of Nottingham, who studies the effects of radio waves on nematode worms as part of the MTHR programme. 鈥淭here was an element of naivety.鈥�

鈥淚t was a nice idea,鈥� agrees Zenon Sienkiewicz, a scientist with the UK鈥檚 National Radiological Protection Board, who is doing MTHR research into the effects of radio frequencies on the brain. 鈥淲ith experience we realised that it was optimistic.鈥�

Any research that appears to show an effect has to be reproduced before it can be considered valid, and this has invariably proved difficult, says Nigel Cridland, the scientific coordinator for the MTHR. 鈥淓ventually you come to a point where you say there鈥檚 nothing else useful we can do,鈥� he says. 鈥淏ut we are not at that point yet. We will get answers.鈥�

At the heart of the problem lies a debate that is driven as much by dogma as by research. Physicists insist that the only way radio waves and microwaves can possibly affect living tissue is by heating it. Unlike more energetic forms of electromagnetic waves, such as gamma rays and X-rays, radio-frequency photons lack the oomph needed to break chemical bonds.

Mobile phones, however, emit such low levels of radiation that they cannot heat tissues by more than a fraction of a degree. So how on earth, ask the sceptics, can they possibly pose a health risk? To try to show that they do, researchers can take two approaches. One is to set up lab studies to show, despite what physicists say, that radio waves really can have effects on animals or cells that heating cannot explain. Alternatively, they can do epidemiological studies to find out if, for instance, people who use mobile phones are more likely to get brain cancers than those who don鈥檛.

Both approaches face some serious stumbling blocks. All studies that have claimed to show any non-thermal effects, for instance, have immediately been dismissed by critics who say that the observed effects could easily have been caused by heating. All but one, that is: de Pomerai鈥檚 work on nematodes. Last year, he published work showing a biological effect that produced the exact opposite of what would be expected if heating were actually involved (麻豆传媒, 9 February 2002, p 4).

But as with all the other studies, other groups are finding it difficult to reproduce his results. Critics like Swicord, of course, would say that this is because there is no effect to reproduce. But de Pomerai claims it is hard to reproduce the same conditions, ensuring that cells are exposed to exactly the same amounts and kind of radiation and kept at the same uniform temperatures. One of the aims of the Stewart report was to try to standardise methods to make it easier to reproduce results, but this has proved difficult.

Though de Pomerai is continuing his research, Repacholi sees little point in such lab work aimed at identifying a non-thermal mechanism. After a certain amount of time you have to say enough is enough, Repacholi says. De Pomerai recognises this: 鈥淭he WHO are mainly interested in demonstrable links to human disease,鈥� he says. 鈥淭he only evidence they will ever take seriously is epidemiological studies.鈥�

The WHO is currently running a large-scale epidemiological cancer study involving several groups in 14 countries. The results are due to be published in a few years, and Repacholi says that if they suggest an effect the WHO will continue its investigations.

But the WHO study, too, is under fire before it is even complete. Its strategy is to look back over the medical records of cancer patients and then ask them about their past use of mobile phones. David Neasham of Imperial College London says this retrospective approach is flawed: 鈥淚f someone already knows they have cancer, then this can bias the study.鈥�

Neasham is a member of the team at Imperial, led by Paul Elliot, which is designing the long-term MTHR-backed study. Instead of looking back, after people are diagnosed with cancer, it will monitor people鈥檚 phone use and then see if they can find any link with cancers that develop later in life. Elliot is currently working on a pilot study, and hopes eventually to monitor the mobile phone use and future health of up to 200,000 people. The trouble with this approach is that it will take 10 to 15 years before it yields any results, and the study has not even begun.

If large-scale studies like Elliot鈥檚 do reveal a clear correlation between mobile phone usage and cancer, the mobile industry could be in trouble. Such results, however, will never explain how cellphones cause these health effects. That will leave researchers back at square one, looking for an elusive mechanism that many scientists are convinced does not exist.

If, on the other hand, such studies fail to find any link with cancer, most researchers will come round to Swicord鈥檚 view, that there really is no association. Then we can go back to worrying about the effect of mobile phones on our bank accounts rather than our brains. Either way, we are in for a long wait.