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Sleep easy, smartphone junkies: chronic cell phone users do not run an increased risk of developing brain tumors, according to a new study in Denmark.

Researchers followed nearly 2.8 million Danish cell phone users who'd used cell phones for 11 to 15 years and did not find an accompanying spike in acoustic neuroma, a type of non-cancerous tumor that slowly spreads between the ear and the brain. Those tumors can cause symptoms like ringing in the ears or dizziness and can sometime become fatal.

Of interest is that acoustic neuromas grow in the area of the brain where greater energy emitted from the cellphones is absorbed, compared to other areas of the brain, said Dr. Joachim Schuz, who led the new study.

While the study focused on non-cancerous tumors it represents the latest entry in a still inconclusive debate over the health risks posed by cell phone radiation. The fact that cell phones do not cause acoustic neuromas seems to suggest that cell phones may be less likely to emit carcinogenic radiation.

That seems to contradict a previous study by the World Health Organization's International Agency for Research on Cancer that suggested a link between glioma, a malignant form of cancer, and wireless cell phone use. The apparent gulf between the two studies' findings -- one released in July of 2011, the other in May -- reflect how unresolved the question is.

The IARC study placed cell phone radiation in the same category as carcinogens like the pesticide DDT and gasoline exhaust. That makes cell phones possibly carcinogenic, according to researchers who conducted the study, a reversal from the WHO's previous position that no adverse health effects have been established for mobile-phone use.

Part of the difficulty with such studies is establishing cause and effect, as opposed to simply linking cell phone usage with how prevalent tumors are. Because cell phone use has become ubiquitous, it can be difficult to disassociate cell phone use from other environmental factors. An epidemiologist at Brown who has studied the issue told TIME that he had seen no increase in brain cancer rates even as cell phone uses skyrocketed from zero to five billion people.

It's possible that in 10 or 20 years things could unfold differently, Savitz said. Nonetheless everything I have seen so far points in the opposite directions [of the IARC study].