Danish epidemiologists have some real advantages.
Citizens of the Scandinavian nation gets a unique ID number for life that can be used by researchers to pull together health records, including data from cancer registries, for just about anybody in the country.
Combine that information with lists of all the people who've had personal cellphone accounts in Denmark (going back to the '80s), and you've got a powerful way to search for health risks from mobile phone use. And the technique doesn't require people to remember anything or answer surveys, as some other studies have.
When researchers dug into the cancer data, teasing out cases involving people who'd had cellphones with those who hadn't, they found no increased risk of brain tumors.
Those findings, which build on work from a previous Danish study, was just published in BMJ, the British Medical Journal. More than 350,000 people who'd been cellphone subscribers, many for more than 10 years, were included in the research.
An accompanying editorial by Swedish researchers says the results appear "reassuring" but need to put in the context of previous studies, some of which have suggested a possible link, and trends in national cancer data, overall.
The cancer trends look good actually. Rates of glioma, a brain cancer, in Sweden haven't increased since 1970, despite cellphone usage that has become practically universal there in the last 10 years.
Still, the editorial writers called for continued monitoring of cancer registries and more studies like the one done by the Danes.