Charles F. Stevens of the Salk Institute, La Jolla, Calif., recently chaired a committee that investigated this question. Here is his reply:
"There have been hundreds of studies of the health implications of exposure to low-frequency electromagnetic fields. A committee of the National Academy of Sciences recently reviewed this literature and concluded that there is no consistent and convincing evidence of adverse health effects from residential exposures. The reason for the hedge, 'consistent and convincing,' is that a few positive studies will always turn up when so many have been done. But the positive ones have not been replicated, and no consistent picture of health risk emerges.
"One of the most difficult areas to study is the possible relation between childhood leukemia and exposure to electromagnetic fields (EMFs), which has turned up in a number of epidemiological studies (but not all, and not in the best study). What these studies found was an association between living near large power lines and an increased incidence of childhood leukemia. The problem is that these same studies found no association between the measured strength of EMFs and the leukemia incidence. In other words, living near power lines seems to be associated with leukemia, but the measured field strength is not.
"What could be responsible for this association? Presumably not exposure to EMFs, because if it were, one would expect to see a correlation between measured field intensity and the prevalence of the disease. Houses near power lines tend to be on large, busy streets in older, poorer neighborhoods. Perhaps some environmental factor, such as pollution levels, is the causative agent, but the other possibilities have not been investigated. Unfortunately, the last lingering worries from these epidemiological studies will not go away until the actual causative agent has been identified."
The following is the press release describing the committee's findings:
No Adverse Health Effects Seen from Residential Exposure to Electromagnetic Fields
WASHINGTON -- No clear, convincing evidence exists to show that residential exposures to electric and magnetic fields (EMFs) are a threat to human health, a committee of the National Research Council has concluded in a new report. After examining more than 500 studies spanning 17 years of research, the committee said there is no conclusive evidence that electromagnetic fields play a role in the development of cancer, reproductive and developmental abnormalities, or learning and behavioral problems.
"The findings to date do not support claims that electromagnetic fields are harmful to a person's health," said committee chair Charles F. Stevens, professor and investigator at the Howard Hughes Medical Institute of the Salk Institute in La Jolla, Calif. "Research has not shown in any convincing way that electromagnetic fields common in homes can cause health problems, and extensive laboratory tests have not shown that EMFs can damage the cell in a way that is harmful to human health."
Concern about the health effects from EMFs arose in 1979, when researchers showed that children living close to high concentrations of certain types of electrical wires were 1.5 times more likely to develop leukemia. Because it is difficult, time-consuming and expensive to measure electric fields in a home over a long period, researchers relied on a substitute to estimate the levels of electromagnetic fields to which residents may have been exposed. Using factors such as the size of wires going past the home and distance between the home and power lines, researchers estimated the fields inside.
The Research Council committee's report says that studies in the aggregate show a weak but statistically significant correlation between the incidence of childhood leukemia, which is rare, and wire configurations. It never has been demonstrated that this apparent association was caused by exposure to electromagnetic fields, however. Outside wiring correlates poorly with measurements of actual fields inside the home, in that it accounts for only a fraction of the fields inside. Scientists have tried unsuccessfully to link leukemia to EMFs by measuring fields inside homes of children who had the disease. The results "have been inconsistent and contradictory and do not constitute reliable evidence of an association," the report says.
The weak link shown between proximity to power lines and childhood leukemia may be the result of factors other than magnetic fields that are common to houses with the types of external wiring identified with the disease. These possible factors include a home's proximity to high traffic density, local air quality and construction features of older homes that fall into this category, the committee said.
Cells, Tissues Unaffected
To try to explain and expand on the knowledge gained from early epidemiological studies, researchers have studied the potential effects of EMFs on individual human cells or tissues and on animals. To date, they have found no evidence to show that EMFs can alter the functions of cells at levels of exposure common in residential settings. Only at levels between 1,000 and 100,000 times stronger than residential fields have cells shown any reaction at all to EMF exposure, and even these changes--mainly in the chemical signals that cells send to one another--are not a clear indication of the potential for adverse health effects. In fact, exposure may actually help the body in some subtle ways, for example, by speeding up the healing process after a bone is broken.
Most important, there has been no case in which even tremendously high exposure to EMFs has been shown to affect the DNA of the cell, damage to which is believed to be essential for the initiation of cancer. Similarly, no animal experiments have shown that EMFs, even at high doses, can act as a direct carcinogen or can affect reproduction, development or behavior in animals.
Electromagnetic fields are generated by wires or electrically powered devices and dissipate quickly, like light. When assessing potential impact of EMFs on health, scientists focus mainly on magnetic fields produced by power lines and electric appliances, which can pass through the body and generate small electric currents. Unlike magnetic fields, electric fields themselves lose most of their strength when they pass through metal, wood or even skin. In fact, the strongest of either fields that the body encounters are the electric currents produced naturally when the heart beats or as nerves and muscles function, the report says.
The committee focused on the health studies of low-frequency electric and magnetic fields common in homes. Sources of exposure include transmission and distribution lines and electric appliances, including shavers, hair dryers, video display terminals and electric blankets. The committee did not study in detail occupational exposures, such as those experienced by electrical workers close to higher-frequency power lines.
New research is needed to answer some of the questions that linger after nearly two decades of intensive research, the committee said. Most compelling is the need to pinpoint the unexplained factor or factors causing a small increase in childhood leukemia in houses close to power lines. The precise factors that are related to an increased number of childhood leukemia cases need to be identified.
The committee also called for more research on the relation between high exposures to EMFs and breast cancer in animals already exposed to other carcinogens and on reasons why electromagnetic fields seem to affect the levels of the hormone melatonin in animals, an effect not reproduced in humans.