Back in May, a group of experts from the International Agency for Research on Cancer (IARC) made waves when they warned that mobile phones may indeed raise the risk for some brain tumors.
As I wrote in TIME:
To the surprise of many cancer experts, IARC classified cell-phone-radiation exposure as “possibly carcinogenic to humans.” The panel put cell phones in category 2B on the agency’s willfully unhelpful scale, below sure carcinogens like cigarette smoke and in the same category as the pesticide DDT and gasoline-engine exhaust. “A review of the human evidence of epidemiological studies shows an increased risk of glioma and malignant types of brain cancer in association with wireless-phone use,” Dr. Jonathan Samet, the chairman of the IARC working group, told reporters the day the study was released.
I warned readers then that the IARC’s conclusion was tentative at best, and that the argument over the potential dangers of cell phones was far from over. And here drops the other shoe — or study.
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In a new paper in the American Journal of Epidemiology researchers looked at data from more than 2.8 million Danish adults, and found that those who had used a cell phone for 11 to 15 years were no more likely than new users or non-users to develop acoustic neuromas — a kind of brain tumor that develops near the ear, where cell phones would be used.
Among the nearly three million Danish adults they had data for, just over 800 were diagnosed with acoustic neuroma between 1998 and 2006. And those who’d used cell phones the longest — at least 11 years — had no greater risk than shorter-term users or non-users.
On top of that, [study author Joachim] Schuz said in an email, there was no indication that long-term cell users had larger-than-expected tumors. Nor did they have a tendency to develop acoustic neuromas on the right side, where most held their phone.
(By the way, Schuz works for the IARC, the same World Health Organization’s body that issued the earlier warning against cell phones.)
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Schuz’s study echoes a recent review in the journal Environmental Health Perspectives, which looked at the results of the controversial Interphone study on cell phones and cancer — which I wrote about last year — and concluded that it was unlikely that mobile phone radiation would cause an increase in tumors.
The authors wrote:
While one cannot be certain, the trend in the accumulating evidence is increasingly against the hypothesis that mobile phone use causes brain tumors.
The key words here: “one cannot be certain.” Critics of the review noted that the authors received funding from the mobile phone industry, which would seem to have a stake in a certain outcome. And Schuz acknowledged that his study was far from comprehensive:
One problem, according to Schuz, is that even long-term cell phone users had not been using their devices all that long.
Acoustic neuromas generally grow slowly, and years may pass between a person’s first symptoms and a diagnosis, Schuz noted.
“As most cell phone users started their use only from the early 1990s onwards,” he said, “we have only up to 15 years of observation time of larger numbers of users — which is perhaps too short to see an effect, if there is any.”
Indeed, researchers keep coming back to that problem: brain tumors take decades to develop, longer than most of us have been using cell phones. There are also questions about the lag time in studies, and whether they accurately capture what might happen to heavy users.
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Still, your own judgment about the risks of cell phone use will come down to your personal prejudices. If you believe cell phones are guilty until proven innocent — and if you believe cell phone companies have something to hide — you’ll be wary. If not, you’ll likely be comforted by the studies that show little indication of harm. But what you’ll almost certainly never get is an absolute answer from medical science.
Bryan Walsh is a reporter at TIME. Find him on Twitter at @bryanrwalsh. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.