With a pending World Health Organisation report on the effects of mobile phone usage on the brain, the evidence so far is pointing to good news. However, much is still unknown.
Is your mobile phone giving you a brain tumour? Yeah, nah, maybe: depending on who you listen to, all of the above may be true.
At the end of October a flurry of news reports kicked off another round in a debate that has been raging for 20 years. "Long-term use of mobile phones 'may be linked to cancer'," proclaimed London's Daily Telegraph. A few days later, by the time the story got to Fox News it had become: "WHO to announce cellphone, brain tumour link."
In fact there was no announcement, just speculation on what might be in a long-awaited report yet to be released. Most research to date finds no link between brain tumours and cellphone use. There is, however, a small question mark about "heavy" mobile phone users - although the data about such cellphone devotees isn't at all clear.
Based on what we know today, cellphone tumour remains rumour.
The report that many are hoping will clarify the picture is the final results paper of the Interphone study - a 20 million (NZ$45.5 million), decade-long international collaboration overseen by the World Health Organisation (WHO). It's due out soon, but no one is saying when.
"It will be the largest study ever taken on the cause of brain cancer and the largest study taken of the link, if there is one, with cellphone use," says Professor Alistair Woodward, who oversees the New Zealand arm of the Interphone investigation.
About half the 13 countries participating have already published their results. The New Zealand study involved 156 cases of cellphone users in the 30-59 age group who had brain tumours, and 172 matched controls. Like most of the results from other countries published to date, its finding did not support an association between the use of cellphones and brain tumours.
"The finding is, overall, there is no association," says Woodward, who is head of the School of Population Health at Auckland University. "But then when you look closely there are these wrinkles."
He's talking about the rather odd finding of what seems to be a reduced risk for light and moderate users, which is difficult to fathom. Could using a phone a little bit actually reduce cancer risk? At the other end of the scale, there is the suggestion of a slightly increased risk for the top 20 per cent of cases - the heaviest users, on their phone several hours a day.
The New Zealand study published in 2007 found some evidence of an increase in risk of glioma - a particular brain tumour that arises in the glial cells in the brain - among the highest levels of regular users. It also found the tumours occurred in parts of the brain likely to receive the highest doses of radio-frequency radiation - in other words on the side of the head on which they used the phone. Other published studies have also found similar suggestions for other types of tumours.
As Woodward and other researchers see it, there are two possibilities: "Is this a consequence of some systematic error in the way the study is put together? Or is it evidence of a small effect that emerges only in the very heaviest users and possibly over an extended period of time?"
The main problem with the research is "recall bias". Ask somebody if they were using a cellphone 10 years ago and you get an answer that is not too bad, says Woodward. But then ask how much on average they were using their cellphone every day and people struggle to remember.
Knowing the information is going to be "noisy", Woodward says the Interphone researchers have done everything they can to smooth out the static. That includes comparing reported usage with phone records when they are available, and running experiments with users given specially engineered phones that log usage.
What they've found is that heavier users tend to over-report more than light users and extremely heavy users sometimes provide reports that seem totally implausible. There are also concerns that there might be a difference in the quality of information given between people who have the disease and those who haven't - the worry being that those who have a brain tumour might unconsciously over-report.
Cellphones were introduced into New Zealand in the early 80s, but not taken up widely until the end of the 80s. Which means there have been 20 years to figure this problem out. Surely by now we should know if these ubiquitous devices are a health hazard? Hasn't someone tracked actual phone usage by phone records and correlated it with the incidence of brain cancer?
Yes they have, says Woodward, but the biggest cohort studies, begun in the US in the mid-80s, had to be abandoned because of privacy concerns.
Some countries, such as Denmark, have been able to do cohort studies which have shown no association with cancer risk. And plenty of studies are now under way, but will not deliver results until after 10 to 15 years.
In the meantime Woodward says the most comforting piece of evidence is that over the 25 years since cellphones have gone from being uncommon to common, the incidence of brain tumours in New Zealand and other countries where they're carefully recorded has scarcely changed.
"That says if there is an effect it's a modest one," says Woodward, although he does admit there is still the possibility that the induction period for brain tumours from cellphone use is longer than 15 years.
It's also worth noting that the longer-term studies have all looked at adult populations. While many are expressing concerns about the effects of cellphone radiation on growing children's brains not much is known about the long-term effects on the cohort that has grown up with cellphones and began using them from an early age.
The other puzzling aspect is that after 15 to 20 years of quite close examination, if there is an effect from radiation fields, scientists still don't know what biological mechanism might be operating. Subtle physiological changes have been detected and replicated in labs, but they don't provide any clear pathway that might be connected to the incidence of cancer.
The point is taken up by Dr Bernard Veyret, a member of the International Commission for Non-Ionising Radiation Protection, a group affiliated with the World Health Organisation which sets the international guidelines on limits for exposure to electromagnetic radiation, including emissions from mobile phones. In Sydney last week, Veyret outlined the types of investigation to date, including cell models and animal studies.
"We have no evidence of genotoxicity or gene expression. It's broadly negative what we have learned from the cell models," he says.
Animal studies are similarly inconclusive. Veyret says studies show cellphone radiation fields have no effect on the the permeability of the "blood-brain barrier" that protects the brain from the toxic compounds in the blood. Human studies have shown possible effects on sleep patterns and EEG results. But concerns that electro-hypersensitive people are more prone to field effects are discounted by double blind studies.
Like most countries, New Zealand has a standard which covers exposure to all sources of radio frequency fields from hand-held devices to transmitters in the 3KHz to 300GHz range. For cellphones it's a specific absorption rate (SAR) - the rate at which energy is absorbed by the body when exposed to a radio frequency - of 2 watts per kilogram (2W/kg) which is typical of other jurisdictions although many use the slightly lower 1.6W/kg.
In light of what's currently known, many jurisdictions are promoting a more precautionary approach to cellphone use than New Zealand's - with some suggesting there should be restrictions on children's use.
"I can't say that there is any good evidence to support that," says senior science adviser for New Zealand's National Radiation Laboratory Martin Gledhill. "We say it's up to parents to decide what they think is best for their children. We do say if you are concerned there are some fairly simple things you can do."
That includes using hands-free kits, only using your phone in a good signal area (in low signal strength areas phones boost their power output) and using newer generation phones which use much less power. Gledhill says the latter point is particularly significant and brings into focus the fact that many users may be getting more exposure from cordless phones in the home. He points out that, typically, a cordless phone produces about 10 milliwatts (mW) whereas newer generation phones in an area of reasonable signal are probably producing as little as one milliwatt.
Gledhill says the ministry regularly monitors the research and re-evaluates its position on adverse health effects. "We have to be guided by the science and knowledge we do have and do the best we can to extrapolate into the areas where we'd like to know more. It would be hard to justify restrictions on cellphone use or recommendations on cellphone use especially given the trends for decreasing exposure anyway."
If you are concerned about cellphone use, here are three simple steps to reducing exposure to cellphone radiation: Use a hands-free kit
Only use your phone in a good signal area
Use newer generation phones which use much less power Over the 25 years since cellphones have gone from being uncommon to common, the incidence of brain tumours has scarcely changed.