(USA TODAY) -- A large new study is the latest to find no link between rising cellphone use and rates of brain cancer.

Researchers in four Scandinavian countries found no increase in brain tumor diagnoses from 1998 to 2003, when cellphone use in those countries grew sharply, according to a study published online Thursday in the Journal of the National Cancer Institute.

That's consistent with most other studies, including a U.S. study that examined brain tumor rates from 1987 to 2005. The International Agency for Research on Cancer also has been conducting a long-term, multinational study, the results of which are to be released in a few months.

Some people have worried about cellphones because they emit radio waves, a form of non-ionizing, low-frequency radiation. This kind of radiation is too weak to damage DNA, however, and scientists know of no biological processes by which radio waves might cause brain cancer, the American Cancer Society's Michael Thun says.

Other types of radiation, such as that produced by an atomic bomb, are known to cause cancer, Thun says.

Researchers in Denmark, Finland, Norway and Sweden, who looked at rates of brain tumors called gliomas and meningiomas dating to 1973, acknowledge their study has limitations.

It's possible that their study population of 16 million adults was too small to detect a very slight increased risk, especially if brain tumors are developing in particular subgroups, according to the study.

It's also possible that brain tumors take more than five to 10 years to develop, says Melissa Bondy of M.D. Anderson Cancer Center in Houston.

Bondy notes that there are major hurdles to studying links between cellphones and cancer. Even if the study had found an increase in brain tumor rates, that doesn't mean cellphones are to blame. Studies such as this can find relationships, but they can't prove one thing caused another. Lots of other trends can help explain changes in disease rates.

People who remain concerned about cellphones can almost eliminate their exposure to these radio waves by using headphones, speaker phones or Bluetooth headsets, Bondy says. "Let's be precautionary, especially in children, because their brains are still developing," Bondy says.

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