The biggest study ever to examine the possible connection between cellphone use and cancer has found no evidence of any link, suggesting that billions of people who are rarely more than a few inches from their phones have no special health concerns.
The Danish study of more than 350,000 people has concluded that there was no difference in cancer rates between people who had used cellphones for about a decade and those who did not.
Last year, another large study found no clear connection between cellphone use and cancer. But it showed a hint of a possible association between very heavy phone use and glioma, a rare but often deadly form of brain tumor. However, the numbers of heavy users was not sufficient to make the case.
That study of more than 14,000 people in multiple countries, in addition to animal experiments, led the International Agency for Research on Cancer to classify electromagnetic energy from cellphones as "possibly carcinogenic," adding it to a list that also includes things such as coffee and gasoline engine exhaust.
But that designation does not mean the phones necessarily pose a risk. Cellphones do not emit the same kind of radiation as that used in some medical tests or found in other sources such as radon in soil.
Two U.S. agencies -- the Food and Drug Administration and the Federal Communications Commission -- have found no evidence that cellphones are linked to cancer.
Yet fears of a link persist, despite the fact that cancer rates have not risen since cellphones were introduced.
In the latest research, published online Thursday in the journal BMJ, researchers updated a previous study examining 358,403 cellphone users age 30 and older in Denmark from 1990 to 2007.
They found that cancer rates in people who used cellphones for about 10 years were similar to rates in people without cellphones. Cellphone users were also no more likely to get a tumor in the part of the brain closest to where phones are usually held against the head. The study was paid for by the government's Danish Strategic Research Council.
"Our study provides little evidence for a causal association, but we cannot rule out a small to moderate increase in risk for subgroups of heavy users," said Patrizia Frei, of the Institute of Cancer Epidemiology in Copenhagen, Denmark, one of the paper's authors.
"This is encouraging news, but it doesn't mean we're at the end of the road," said Hazel Nunn, head of Health Evidence and Information at Cancer Research U.K., which was not linked to the study.
Nunn said studies with longer-term data were still needed.