Living near high-voltage power lines raises children's risk of leukemia by 69 percent, a British study shows.
That doesn't prove that power lines cause the deadly blood cancer, the study's authors are quick to point out. Despite 30 years of research, scientists still can't come up with a plausible reason why the weak magnetic fields near power lines might cause leukemia.
Gerald Draper, DPhil, director of the childhood cancer research group at Oxford University, led the study. Draper's team compared more than 29,000 children with cancer, including 9,700 children with leukemia, to age-, sex-, and birthplace-matched children without cancer. The children's birth homes were located on the power grids of England and Wales.
Compared with children who lived more than 600 meters from a high-voltage power line, those who lived within 200 meters of the power lines had a 69 percent greater risk of leukemia. Those living 200 to 600 meters from power lines had a 23 percent higher risk of leukemia. The findings appear in the June 4 issue of the British Medical Journal.
There is a slight tendency for the birth addresses of children with leukemia to be closer to these lines than those of children matched for comparison, Draper and colleagues write. "We have no satisfactory explanation for our results in terms of causation by magnetic fields, and the findings are not supported by convincing laboratory data or any accepted biological mechanism."
An Unusual Disclaimer
That's an unusual disclaimer for a researcher who has found a statistically significant link. But the data leave Draper and other experts scratching their heads for an explanation.
There are many theories about how power lines might cause leukemia. The most obvious one is that the magnetic fields created by power lines somehow make cancer cells grow in susceptible people. But there's a problem with this theory, notes Heather Dickinson, PhD, principal research associate at the Center for Health Services Research at the University of Newcastle in England.
"What is puzzling is that the magnetic field from power lines is only 1 percent of the earth's magnetic field, which surrounds us all," Dickinson tells WebMD. "Your fridge or vacuum generates a magnetic field of about the same strength. In England and Wales, only 5 percent of the exposure to magnetic fields comes from high voltage pylons. So if this is a hazard, people with appliances should be just as concerned."
John E. Moulder, PhD, director of radiation biology at the Medical College of Wisconsin, is an expert on how exposure to various kinds of electromagnetic fields and radiations might cause cancer.
"Power lines cannot be proven absolutely safe," Moulder tells WebMD. "But people have looked very hard for a causal relationship between power lines and cancer and nobody has found one. People aren't going to like this. They really want to be told we are absolutely sure one way or the other, and we are not."
Moulder, like Dickinson, points out that animals exposed to strong magnetic fields -- much stronger than those found near power lines -- don't get cancer.
In June 2002, the U.S. National Institute of Environmental Health Sciences updated its 1999 report on possible risks from electromagnetic fields (EMF).
"Over the past 25 years, research has addressed the question of whether exposure to power-frequency EMF might adversely affect human health. For most health outcomes, there is no evidence that EMF exposures have adverse effects," the NIEHS report concludes.
Power Lines and Infections
Dickinson suggests that the Draper team's findings are real. But she thinks that living near power lines is linked to something else -- something that really does increase a child's leukemia risk.
“We know the rate of leukemia varies by a factor of two or three between isolated rural areas," Dickinson says. "And this is related to an influx of population that can change pattern of the infections to which a child is exposed."
Sudden exposure of once-isolated children to a lot of new childhood diseases, Dickinson suggests, may be linked to leukemia risk. She suggests that this may be a "confounding factor" in the Draper team's findings.
But even if living near power lines does raise a child's risk of leukemia, Dickinson notes that the risk is small.
"A 70 percent increase in leukemia means that the 1 in 2,000 risk of leukemia becomes a 1 in 1,200 risk," she says. "In the U.K., this means that five extra children might get leukemia. We need to keep this in perspective -- look at the thousands of children hurt in road accidents each year."
SOURCES: Draper, G. British Medical Journal, June 4, 2005; vol 330: pp 1290-1295. Dickinson, H.O. British Medical Journal, June 4, 2005; vol 330: pp 1279-1280. Heather Dickinson, PhD, principal research associate, Center for Health Services Research, University of Newcastle, England. John E. Moulder, PhD, professor and director of radiation biology, department of radiation oncology, Medical College of Wisconsin, Milwaukee.