Brain tumors among cellphone users are not clustered within range of most of the radiation emitted from the devices, a new report finds - suggesting that mobile phones do not cause cancer.
Moreover, people who had used mobile phones for the longest amount of time, and spent the most time on the phones, were no more likely to experience tumors located within 5 centimeters of the phone, where "90 percent of the radiation" is emitted, study author Dr. Suvi Larjavaara from the University of Tampere in Finland told Reuters Health.
These findings appeared as the World Health Organization announced that, upon review of available scientific evidence, cellphones should be classified as "possibly carcinogenic."
Although the results of the Finnish study may be reassuring, they are certainly not conclusive, Larjavaara cautioned. Cancer can take a long time to develop, and only 5 percent of the people included in the study had been using mobile phones for at least 10 years, the authors note in the American Journal of Epidemiology.
Larjavaara acknowledged that these latest findings contradict the WHO's latest announcement, which placed cellphone use in the same cancer risk category as coffee and chloroform. The WHO had previously said there was no established evidence for a link between cellphone use and cancer.
"Our evidence does not support the connection, but obviously a majority does," she told Reuters Health by email.
Overall, the evidence remains conflicted: Last year, a study including 13,000 cellphone users over 10 years found no clear answer on whether the mobile devices cause brain tumors. Another study from last February suggested that using a mobile phone can change brain cell activity.
Use of mobile phones has increased hugely since their introduction in the early- to mid-1980s. About 5 billion mobile phones are currently in use worldwide.
One issue that arises when studying the risks of cell phone use is that people often don't recall how much time they spend on the phone. To approach the question more scientifically, Larjavaara and colleagues looked at the location of tumors, reasoning that an excess of tumors close to the phones would implicate the devices.
Ninety percent of the radiation released from phones is absorbed by the brain tissue located within 5 centimeters of the handset. So in 888 brain tumors diagnosed between 2000 and 2004, the researchers mapped the exact location of the tumor within the brain, relative to where people would place a cell phone while talking.
This study was one of the papers included in the WHO's recent analysis of cancer risk from cellphone use, along with two others by Dr. Elisabeth Cardis at the CREAL-Center for Research in Environmental Epidemiology in Barcelona, who reviewed the latest findings for Reuters Health. That analysis is scheduled to be released on July 1.
Cardis said that she and her team have also looked at tumor location in cellphone users, but instead developed a formula to calculate the amount of energy present at the actual tumor, factoring in the characteristics of the phone and network, among other variables.
In this analysis, they found that tumors in long-term cellphone users did occur more often in locations with higher exposure from cell phones, Cardis said.
The current study considered the entire phone as a source of exposure, since many phones have an integrated antenna, and therefore measured the distance of tumors from any point on the phone.
This definition of exposure "is overly simplistic, in my opinion," Cardis said in an email, because previous studies have found that the most exposed area is generally located around the ear.
"I expect there is substantial misclassification of exposure in the analyses published in the American Journal of Epidemiology, and hence it is not possible to draw conclusions about the presence or absence of a risk," she concluded.