In 1979, scientists published the first study associating extremely low frequency electric and magnetic fields—such as those produced by high voltage power lines—with an increased risk of cancer. Over the next two decades, researchers narrowed the connection to magnetic fields and increased risk of childhood leukemia , a cancer of the white blood cells.

In 2001, the International Agency for Research on Cancer classified extremely low frequency magnetic fields as “possibly carcinogenic.” They noted, however, that the scientific evidence for this claim was “limited.”

Much remains unknown about the relationship between magnetic fields and cancer. For example, if a relationship does exist, during which period of childhood is exposure to magnetic fields dangerous? For how long does a child have to be exposed to these magnetic fields to be at increased risk for leukemia? And, most importantly, how do magnetic fields cause leukemia?

A study published in the June 4, 2005 British Medical Journal strengthens the association between childhood leukemia and extremely low frequency magnetic fields. It reports that children who lived within 200 meters (656 feet) of a high voltage power line at birth were 70% more likely to develop childhood leukemia than children who lived more than 600 meters (1969 feet) away.

About the Study

This was a case-control study, meaning that a group of children with cancer was compared to a group of children without cancer with respect to how close they lived to a high voltage power line at birth.

The researchers searched cancer registries to identify 29,081 children aged 0 to 14 years, with cancer (of these children, 9,700 had leukemia.) The children were all born in England or Wales between 1962 and 1995. The children with cancer ( case patients) were matched with healthy children ( control patients) who were the same gender and age (within six months) of the case patients, and who had been born in the same birth registration district.

The researchers calculated the distance from the home address at birth of all of the children to the nearest high voltage power line that had existed at the time.

The Findings

Children who lived less than 200 meters away from a high voltage power line at birth were 70% more likely to develop leukemia than children who lived more 600 meters away at birth. Children who lived between 200 and 599 meters away from a high voltage power line at birth were 23% more likely to develop leukemia than children who lived more than 600 meters away. The increased risk remained, even after the researchers took the children’s socioeconomic status into consideration.

Proximity to high voltage power lines did not increase the risk for any other type of cancer.

This study has a few important limitations. First, case-control studies are by nature susceptible to sampling bias. In other words, the researchers may have selected control patients that lived further away from power lines by chance; another set of controls may have lived closer to the power lines than the case patients. Second, the researchers were not able to estimate or measure the magnetic field from the power lines, so the researchers could not know what level of magnetic fields the children were actually exposed to.

How Does This Affect You?

For more than 25 years, scientists have suspected that extremely low frequency magnetic fields, such as those produced by high voltage power lines, may increase the risk of childhood cancers, particularly leukemia. This study adds to that evidence, finding that children living closer to high voltage power lines at birth were significantly more likely to have leukemia than children living further away.

But these findings should be put into perspective. Even if proximity to high voltage power lines increased the risk of childhood leukemia as much as reported in this study, power lines would only be associated with about five of the 400 to 420 cases that occured in England and Wales each year.

One of the more surprising findings of this study, was that even children who lived a moderate distance away from high voltage power lines at birth—at a distance where the level of magnetic fields is believed to be extremely low—were more likely to develop leukemia than children who lived more than 600 meters away. Add that to the fact that there is still no clear data indicating how magnetic fields might cause leukemia. The question must be raised as to whether something associated with power lines, other than magnetic fields, might be at play.

As the population continues to grow, more and more housing developments are likely to occupy the same space as high-tension power lines. The scientific evidence to date, although suggestive of a health risk, is unlikely to cause changes in zoning laws and mass relocations of residences. Even without firm evidence, it seems clear that most parents would prefer to raise their young children as far away from these electromagnetic fields as possible. Many will not have that choice.