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Using cell phones, even over a long period of time, does not appear to raise a person's risk for cancer, Danish researchers report. Their study, which appears in today's Journal of the National Cancer Institute, is the first to include people who had used cell phones for as long as 21 years.

Why it's important: Because cell phones emit a type of low-energy radiation, there is concern that using them over a long period of time could lead to cancer, especially in the brain. The growing popularity of cell phones makes it important to learn if this technology actually does have an effect on cancer.

What's already known: Of 16 previous studies looking at cell phone use and brain tumors, only 2 have found any link, says Michael Thun, MD, MS, the American Cancer Society's vice president of epidemiology and surveillance research. However, the methods used in those 2 studies led many researchers to question the findings. One problem researchers face is that cell phones are relatively new devices, so there aren't a lot of people who have used them for more than about 10 years. It can take longer than that for some cancers to develop, so it's not clear whether using cell phones for more than 10 years might pose a problem.

How this study was done: The Danish researchers tried to address this problem by including people who had begun using cell phones as early as 1982. They looked at cell phone records for more than 420,000 adults in Denmark, and compared those to cancer cases listed in the Danish national cancer registry. They were looking to see if the number of cancer cases among cell phone users was different from what would be expected in the general population. That's a way of finding out whether cell phone users have a higher or lower cancer risk than other people. People who had had cancer before getting a cell phone were excluded from the study.

What was found: The overall number of cancers among cell phone users (14,249) was about the number expected (15,001). Cell phone users did not have a higher risk of brain or central nervous system cancers, salivary gland tumors, eye tumors, or leukemia. This was true even for people who had used cell phones for longer than 10 years. In fact, these long-term users appeared to have a lower risk of brain cancer. The researchers don't have a good explanation for that; they think it might be a chance finding and say more studies are needed.

The bottom line: Thun calls the new findings "reassuring," but not the final answer.

Citation: "Cellular Telephone Use and Cancer Risk: Update of a Nationwide Danish Cohort." Published in the Dec. 6, 2006 Journal of the National Cancer Institute (Vol. 98, No. 23: 1707-1713). First author: Joachim Sch?nish Cancer Society.

（英語點津 Annabel 編輯）