|Power Lines-Leukemia Debate Lingers|
Study shows slight increase in risk, but magnetic fields may not be to blame
By Steven Reinberg
FRIDAY, June 3 (HealthDayNews) -- Over the past 26 years, there has been an ongoing debate as to whether living under or near high-voltage power lines increases the risk for childhood leukemia.
Now a new, large British study finds a slight increased risk, but not necessarily due to power lines themselves.
"We found that there was a slight increase in leukemia within 200 meters of one of these power lines. And an even slighter increase within 600 meters," said lead researcher Gerald Draper, an Honorary Senior Research Fellow from the Childhood Cancer Research Group at the University of Oxford.
However, he said, this increase "cannot be a direct effect of magnetic fields. Our finding doesn't fit in with even the small amount of evidence that magnetic fields can cause childhood leukemia."
High-voltage electric power lines produce very low frequency electric and magnetic fields. Since 1979, there has been concern that these fields may cause an increased risk of cancer. In 2001, the International Agency for Research on Cancer said that extremely low frequency magnetic fields may be possibly carcinogenic. However, others, such as the U.K. Childhood Cancer Study, dispute this.
In their study, Draper's team collected data on more than 29,000 children with cancer in England and Wales born between 1962 and 1995, including 9,700 children with leukemia. They compared these children with data on similar children who did not have cancer.
The report appears in the June 4 issue of the British Medical Journal.
Draper's group found that children living within 200 meters of high-voltage power lines at birth were at a 70 percent increased risk of leukemia compared with those who lived beyond 600 meters. They also found a slightly increased risk for children living 200 to 600 meters from the lines at birth.
According to Draper, in absolute terms that means that about five of the 400 to 420 cases of childhood leukemia occurring annually in England and Wales may be associated with power lines. There was no increased risk for other childhood cancers, the researchers report.
These findings are puzzling, Draper said. "You would not expect any effect of magnetic fields to go out that far from power lines," he explained.
Draper said he's stumped as to the reason for this association. He speculates there may be something about power lines that is not understood. "But since no one understands it, we can't tell you what it is," he said.
"It may not have to do with power lines at all," he added. "It's to do with the sort of people who live around power lines or other things going on." Beyond that, Draper feels the association between power lines and leukemia could be simple coincidence. "It could be due to chance," he said. "We'd probably put a bit of money on that, and a bit of money on the fact that it's some other factor, which we don't understand."
Draper said there is really nothing to worry about in terms of children getting leukemia from power lines. "No one should look at our study and say 'That means I've got to take some action,'" he said." The people who live very near to big power lines might want to get some measure of their own exposure."
In an accompanying editorial, Heather Dickinson, a principal research associate from the Centre for Health Services Research at the University of Newcastle upon Tyne, reviewed the most likely causes of childhood leukemia.
Dickinson said that the causes of childhood leukemia are most likely common infections that interact with gene damage to the fetus occurring during gestation and shortly after birth.
"Leukemia is a disease of the immune system," Dickinson said. "And the child's immune system may be damaged before birth."
"In addition, protecting children from common infections may actually increase the risk for developing leukemia," Dickinson noted. "Babies and children in our affluent society are much more protected from infections than they used to be. The immune system needs to be challenged by infection if it's going to develop normally. If they don't have this strong, normal immune system, they are more vulnerable to having an abnormal response when they have a challenge from infection."
Dickinson doesn't think much of the connection between power lines and leukemia, "The power line hypothesis has been rumbling on for the past 20 years," Dickinson said. If the hypothesis were true, then one would expect to see increasing risk with increased magnetic exposure, but studies haven't shown this, she said.
Dickinson pointed out, "Road accidents are a much greater cause of injury and death among children than high-voltage power lines could possibly be."
Another expert thinks that the power line/leukemia connection is tenuous. "This issue continues to be difficult to figure out," said Dr. Michael Thun, a vice president and epidemiologist for surveillance research at the American Cancer Society.
"What's clear is if power lines do contribute to the risk of leukemia, it's a very small fraction of the overall risk," he said. "What's not clear is if they actually contribute at all, and if so, how."
The Medical College of Wisconsin can tell you more about power lines and cancer.
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SOURCES: Gerald Draper, D.Phil., Honorary Senior Research Fellow, Childhood Cancer Research Group, University of Oxford, U.K.; Heather Dickinson, Ph.D., principal research associate, Centre for Health Services Research, University of Newcastle upon Tyne, U.K.; Michael Thun, M.D., vice president, epidemiologist and surveillance research, American Cancer Society, Atlanta; June 4, 2005, British Medical Journal