A long-awaited international study has found no evidence of increased risk of brain tumors associated with mobile phones, but said the findings were not definitive and called for more research.

“The possible effects of long-term heavy use of mobile phones require further investigation,” the study said.

Critics of the decade-long Interphone study, published Tuesday in the International Journal of Epidemiology, argue that the research methodology was flawed and that the study lacks a definitive conclusion.

“I’m not telling people to stop using the phone. I’m saying that I can’t tell you if cell phones are dangerous, but I can tell you that I’m not sure that they are safe,” said Dr. Devra Davis, professor of Preventive Medicine at Mount Sinai Medical center in New York.

She particularly cited the study’s exclusion of children and young adults, the mobile phone’s increased popularity since the study period, the fact that only two types of brain tumors were studied and Interphone’s definition of a “regular” user is not consistent with cell phone use today. She also noted that the study’s control groups were unorthodox.

“Their comparison isn’t between people who used cell phones and didn’t. It was between people who used their phone less than once a week, and more than once a week, all on self-reflection memory of their mobile use, the day after they’ve had a brain operation.”

The study defined regular cell phone user as ever having one phone call a week for at least six months. The results of the study were based on patients’ average talk time ranging from 120 minutes to 150 minutes a month; most users today far exceed that. It’s “what some people in the U.S. would use in a week in 2010,” Davis said.

The study was conducted at 16 locations in 13 countries, not including the United States. In hospital interviews, brain tumor patients were asked to answer a series of questions based on memory about their mobile phone use habits prior to being diagnosed. They were asked to reflect on how many hours they talked on their phone a month, how long they had been using their cell phone, if they remembered how many phone calls they made a month and to what side of the head they typically held the phone.

The study focused on two types of tumors – glioma and meningioma.

The study was funded in part by the cell phone industry. Several of the researchers analyzing the data acknowledged that they received money from the mobile phone industry.

(Source: CNN)