A study of nearly 400,000 adults living near power lines in Finland--the largest survey of its kind--offers no evidence that exposure to the low-level magnetic fields they generate increases the risk of cancer. The research, published in the 26 October British Medical Journal, found that rates for 21 cancers were no higher than normal.
``This is a strong study,'' says epidemiologist Richard Stevens of Battelle Pacific Northwest Laboratory, who has studied electromagnetic fields. He says it demonstrates that ``living close to transmission lines does not increase the risk of cancer--at least in Finland.'' But Stevens gives two key reasons why the results should not be seen as conclusive evidence against any cancer risks. A person's exposure to magnetic fields was based on a calculation rather than a direct measurement, he notes, and workplace exposure was not monitored.
The Finnish group, led by Pia Verkasalo of the University of Helsinki, compiled census and cancer registry data for 383,700 adults who lived for some period between 1970 and 1989 in buildings within 500 meters of high-voltage overhead power lines. Researchers used several measurements--such as distance from power lines and utility company power-usage records--to estimate each person's exposure to magnetic fields, then correlated exposure with disease. Of the 21 cancers examined, about 8587 cases would have been expected in the group. But the researchers found only 8415 cancers--2% fewer, a statistically insignificant decrease. The cancers included breast cancer, brain cancer, and leukemia, all of which have been linked to magnetic fields. Cancers in some narrow categories showed a slight increase, but Verkasalo says those results may be due to chance.
The study won't end the debate over magnetic fields, however. Several studies have found a link between childhood leukemia and power lines, for example, and others suggest workers exposed to magnetic fields have higher rates of some cancers. Those questions, Verkasalo says, ``still aren't settled.''