Cell-phone use does not appear to cause brain tumors, at least during a period of two to three years, according to two large new studies released today.
The studies, which involved 1,250 brain tumor patients and an equal number of healthy individuals, found no increased risk of cancers among those who used the electronic devices more frequently.
The studies are not likely to put the issue of potential harm completely to rest, but they join a growing body of evidence suggesting that the only important risk associated with the handheld devices is a higher likelihood of traffic accidents.
"In all of the available scientific literature, there is nothing that indicates any adverse health effects from using cell phones," said Russell Owen, chief of the Food and Drug Administration's radiation biology branch.
One of the new studies is published in today's Journal of the American Medical Assn. The second is scheduled to be published next month in the New England Journal of Medicine, but was posted on the journal's Website Tuesday.
The two studies leave open the question of whether longer use of the devices could pose a problem. That issue is being addressed in a still larger European study now under way, but results are not expected until 2003 at the earliest.
"The question that is important to bear in mind at this point is, have there been any studies that clearly point to an increased risk of brain cancer from cell-phone use?" said Dr. Peter Inskip of the National Cancer Institute, lead author of the New England Journal study. "I believe that the answer is no. Does that mean we can prove they are safe? No."
Critics have been concerned about the possibility of hazards from cell phones since the early 1990s because the devices transmit radiofrequency energy from an antenna held next to the head.
Although the radiation is not at a frequency that would damage DNA, some phones emit microwave radiation that could heat tissue.
Studies have shown, however, that the low power of the phones produces only about a tenth of a degree increase in the temperature of adjacent cells, much less than the normal fluctuation in cellular temperature.
The new studies further support the idea that the fears may have been exaggerated.
But Inskip cautioned that many carcinogens only produce tumors after a long period of time, so that it is important to have long-term studies. For this reason, researchers are eagerly awaiting the European study, which is being conducted by the International Agency for Research on Cancer.