Exposure to extremely low-frequency magnetic fields (ELF-MFs)--emitted by anything from power lines to appliances or improperly grounded wiring--is not likely to increase children's risk of developing brain tumors, the authors of a new analysis conclude.

Researchers have been investigating the health risks of these magnetic fields since 1979, Dr. Leeka Kheifets of the University of California, Los Angeles, and her colleagues note in the American Journal of Epidemiology. There is some evidence that exposure at certain levels may be related to childhood leukemia, they add.

Evidence for a link between ELF-MF exposure and childhood brain tumors is weaker, according to Kheifets and her team, but to date a pooled analysis investigating the association has not been performed. Pooled analyses involve taking data from several different studies of the same topic and analyzing them as a whole, using a variety of statistical techniques to take as many differences between the studies into account as possible.

In their report, the researchers pooled results from 10 studies of childhood brain tumors and ELF-MF exposure conducted between 1960 and 2001. Their analysis included about 8,400 brain tumor cases diagnosed at age 15 or younger and 11,500 healthy controls. Even with such large numbers, the number exposed to high levels of ELF-MF was very small.

Kheifets and her colleagues found no consistent associations between ELF-MF exposure and brain tumor risk, nor did they find any patterns--for example increasing risk with higher levels of exposure--suggesting a relationship.

While there were key differences between the studies, for example in the way exposures were measured, the results remained consistent, the researchers say. Taken as a whole, our results provide little evidence for an association between ELF-MF exposure and childhood brain tumors, they conclude.

Although epidemiological evidence has linked leukemia to ELF-MF exposure, Kheifets said, most animal or laboratory studies do not support a relationship.

Based on what's currently known, she added, it doesn't make sense for someone living close to a power line, for example, to move only because they're concerned about leukemia.

The risks are so low, and the association is so uncertain, that only low- and no-cost exposure reduction is warranted, she said.

For example, parents can take easy measures to reduce their children's exposure to ELF-MFs if they are concerned, she added. If a child sleeps with an alarm clock by the head of their bed, move the alarm clock a few feet away. The strength of ELF-MF exposure is heavily dependent on how close one is to the source, she noted.

New power lines can also be designed to reduce exposure, Kheifets said. One of the study's authors works for the National Grid plc utility company in the U.K., the paper notes. Its authors also acknowledge funding from the Electric Power Research Institute, Southern California Edison and the National Cancer Institute.

We live with uncertainty and we also live with risks, and so there are benefits that need to be weighed in each particular case, she said. These exposures really come from many sources, and that's just part of modern life.

California Medicine Cancer