For the last 18 years, the debate over whether power lines cause cancer has been passionate and sometimes furious. Even when the National Academy of Sciences last November found no evidence of risk, it suggested further research on childhood leukemia.
Now a large, meticulously designed study has found no evidence that electric power lines cause leukemia in children, researchers said Wednesday.
The new study was a collaboration between scientists at the National Cancer Institute and childhood leukemia specialists from the nation's leading medical centers. It involved 636 children with acute lymphoblastic leukemia, the most common childhood cancer, and 620 healthy children who were matched to the cancer patients by race, age and residential neighborhood.
Scientists assessed the children's exposure to magnetic fields that power lines produce, measuring the fields in the children's residences, past and present, and where the mothers lived when they were pregnant. They directly measured the fields in the childrens' yards, schools and day care centers and even had the children walk around with measurement devices. Investigators doing the measurements did not know which children had had cancer.
Then the researchers asked, Did the children who developed leukemia have a higher exposure to magnetic fields?
The answer, published in Thursday's issue of The New England Journal of Medicine, is "no," with one caveat: Those children whose exposure was above .300 micro Tesslas had a slightly higher risk of leukemia. But, the researchers cautioned, there were very few children with these high exposures -- just 45 out of the 638 children with cancer.
And yet at the very highest exposures, the risk went back to almost normal. What this meant to the researchers was that there was no trackable relationship between level of exposure and level of risk, what is normally called a dose-response curve.
Dr. Charles Stevens, a neurobiologist at the Salk Institute in San Diego, and others dismissed the apparent increased risk as insignificant. "If you can't find a dose-response, you can't believe it," Stevens said. Spurious associations are expected when statisticians pore over complex data sets looking for correlations, he added.
Stevens was the head of the committee of the National Academy of Sciences that reported on health effects of electromagnetic fields last November.
Dr. Martha S. Linet, a childhood cancer specialist and epidemiologist at the National Cancer Institute who was the lead author of the new study, said the study was not ambiguous: It found no dangers from magnetic fields induced by power lines.
The anguish over the possible effects of power lines began in 1979 when Dr. Nancy Wertheimer, who was affiliated with the University of Colorado in Denver, and her assistant, Ed Leeper, published a study indicating that children who lived near power lines had a twice the normal incidence of leukemia.
The study was criticized because it was small and relied on inferences rather than direct measurements of exposure to electromagnetic fields. But it became the centerpiece of three terrifying and widely read articles published in the New Yorker magazine in 1989 by the journalist Paul Bordeur. He later wrote a book on the dangers of power lines and he lectures on the subject.
In the meantime, scientists began studies designed to see whether Dr. Wertheimer and Leeper were correct. The studies tended to be small, they often inferred exposure many years after the children had developed cancer, and they had other methodological problems. But some found associations between power lines and cancer.
As the debate continued, an industry sprang up to sell remediation from power lines and parents of children with cancer began suing power companies. Property values dropped for homes near power lines. And, said Dr. Robert Park, a physicist at the University of Maryland and a spokesman for the American Physical Society, there grew up a generation of "dozens of people who have spent their entire professional careers on this one problem."
At the request of Congress, a National Academy of Sciences committee reviewed more than 500 papers on the health effects of electromagnetic radiation. Its report, issued in November of 1996, concluded that the studies taken as a whole failed to provide evidence that electromagnetic fields cause disease.
The group added that further research was needed on the question of power lines and leukemia. Stevens explained that homes near power lines tended to be old and in poor neighborhoods. If children living there got leukemia, perhaps it was because of other factors, like pollutants. He said that the group did not mean to suggest that power lines caused leukemia, but that that was the message people took away.
People are terrified of radiation, Stevens said. "You can't see it and it comes through the walls of the house." Add to that the fear that "it does terrible things to children," and you have a substance that "taps into our primal fears," he said.
Dr. Linet said she did not start the study with her mind made up. "This was the situation we found ourselves in the late 1980s," she said. "A variety of studies had linked a variety of environmental causes to childhood leukemia."
But, she said, the studies were all small, suggestive rather than definitive. Childhood leukemia is rare -- there are only about 1,600 new cases a year in the United States, Dr. Linet said. But its cause was not known. Was there something in the environment or was it a genetic error, the result of bad luck?
The investigators decided to focus on the power-line question. "None of us would have devoted the last eight or so years of our lives to this if there wasn't potentially something in it," Dr. Linet said.
"None of us would have devoted the last eight or so years of our lives to this if there wasn't potentially something in it," Dr. Linet said.
Some say the debates show how hard it is to dispel the public's fears of a threat that has never been demonstrated but that seems terrifying. "It's really true that it's just impossible to get rid of this," Stevens said.
Not everyone is convinced by the new data.
Dr. David Savitz, an epidemiologist at the University of North Carolina, whose small study of Denver children in 1989 had found an association between power lines and childhood leukemia, pointed to the slight increase in cancer risk among children with the highest exposures.
"Don't get me wrong, this is not compelling positive evidence," he said Wednesday. But, he added, further research is needed.
Louis Slesin, the editor of Microwave News, a newsletter that has warned of the dangers of power lines, went further. "I think it's still a wide open question," of whether power lines cause cancer, he said. "We shouldn't close the book yet."
Park disagreed. "The number of questions you can ask is infinite," he said. "If it's not the intensity of the electric field, maybe it's the number of times you turn the field on and off. Many it only causes cancer in conjunction with eating bananas. You can keep asking questions forever." But, he said, at some point, it is time to invest research money in other things.
"I'm ever an optimist," Park said. "My guess is that it's pretty much over now."
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