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source: rfsafe.comWhat have the studies of cancer in people living near power lines found?Of children ages 14 and under, in the United States, about 14 in 100,000 develop some form of cancer each year. Almost one-third of these cases are acute lymphocytic leukemia, the most common form of leukemia in children. For childhood leukemia victims, chances of survival are about 60%. To date, 14 studies have analyzed a possible association between proximity to power lines and various types of childhood cancer. Of these, eight have reported positive associations between proximity to power lines and some forms of cancer. Four of the 14 studies showed a statistically significant association with leukemia. The first study to report an association between power lines and cancer was conducted in 1979 in Denver by Dr. Nancy Wertheimer and Ed Leeper. They found that children who had died from cancer were 2 to 3 times more likely to have lived within 40 m (131 ft) of a high-current power line than were the other children studied. Exposure to magnetic fields was identified as a possible factor in this finding. Magnetic fields were not measured in the homes. Instead, the researchers devised a substitute method to estimate the magnetic fields produced by the power lines. The estimate was based on the size and number of power line wires and the distance between the power lines and the home. A second Denver study in 1988, and a 1991 study in Los Angeles, also found significant associations between living near high-current power lines and childhood cancer incidence. The L.A. study found an association with leukemia but did not look at all cancers. The 1988 Denver study found an association with all cancer incidence. When leukemia was analyzed separately, the risk was elevated but not statistically significant. In neither of these two studies were the associations found to be statistically significant when magnetic fields were measured in the home and used in the analysis. Studies in Sweden (1992) and Mexico (1993) have found increased leukemia incidence for children living near transmission lines. A 1993 Danish study, like the 1988 Denver study, found an association for incidence of all childhood cancers but not specifically leukemia. A Finnish study found an association with central nervous system tumors in boys. Eight studies have examined risk of cancer for adults living near power lines. Of these, two found significant studies involving cancer in people living near power lines. Are there high cancer rates in some neighborhoods close to electric power facilities?Scientists call unusual occurrences of cancer in an area or in time a 'cancer cluster'. In some cases, a cancer cluster has served as an early warning of a health hazard. For most reports of cancer clusters, however, the cause is never determined, or the perceived cluster is not really an unusual occurrence. Concerns have been raised about seemingly high numbers of cancers in some neighborhoods and schools close to electric power facilities. In recent years, three state health departments have studied apparent cancer clusters near electric power facilities. A Connecticut study involved five cases of brain and central nervous system cancers in people living near an electrical substation. The local rates for these types of cancer were found to be no different from statewide rates. Examination of cancer rates at various distances from the substation also failed to show evidence of clustering. In North Carolina, several cases of brain cancer were identified in part of a county that included an electric power generating plant. An investigation showed that brain cancer rates in the county, however, were actually lower than statewide rates. Among staff at an elementary school near transmission lines in California, 13 cancers of various types were identified. Although this was twice the expected rate, the state investigators concluded that the cancers could have occurred by chance alone. CLUSTERS As an analogy, think about how an uncommon family name might be distributed at homes located throughout a city. Would it be unusual to find neighborhoods where two or three unrelated families with this same name live in the same small area? Statistically, this may be shown to be expected due just to chance. While four or more such families may be very unlikely due to chance, this does not mean that it is impossible. One possible cause (other than chance) for some such 'name clusters' is that the families are part of the same ethnic group and they choose to live close together. For perceived neighborhood cancer clusters, however, health agencies generally never find a common environmental cause. It is also apparent that the definition of a 'cluster' depends on how large an area (neighborhood) is included . Cancer cases (x's in graphic) in a city may show patterns that appear to be 'clusters'. They may seem to suggest a common environmental cause. Usually such patters are due just to chance. Further, delineation of a cluster is subjective - where do you draw the circles?
What about the Swedish cancer study of people living near transmission lines?In late 1992, researchers in Sweden reported results of a study of cancer in people living near high-voltage transmission lines. The Swedish study generated a great deal of interest among scientists, the public, and the news media. Relative risk for leukemia increased in Swedish children who lived within 50 m (164 ft) of a transmission line. The risk was found also to increase progressively as the calculated average annual 50-Hz magnetic field increased in strength. However, the risk calculations were based on very small numbers of cases (see summary below). The Swedish researchers concluded that their study provides additional evidence for a possible link between magnetic fields and childhood leukemia. However, scientists have expressed differing opinions about this study. Some scientists believe the study is important because it is based on magnetic field levels presumed to have existed around the time the cancers were diagnosed. Others are skeptical because of the small numbers of cancer cases and because no cancer association was seen with present-day magnetic field levels measured in the home. There are about 70 new cases of childhood leukemia per year in Sweden. The National Electrical Safety Board of Sweden estimates that if, as this study suggests, living overhead transmission lines increases a child's risk of developing leukemia, then approximately two children per year in Sweden would develop leukemia as a result of living near such power lines. SUMMARY OF SWEDISH RESIDENTIAL CANCER STUDY
Source: Feychting & Ahlbom 1992, 1993. Besides cancer, what other kinds of effects have been reported in epidemiologic studies involving EMFs?Several epidemiologic studies have looked for EMF effects on pregnancy outcomes and general health. Various EMF sources have been studied for possible association with miscarriage risk: power lines and substations, electric blankets and heated water beds, electric cable ceiling heat, and computer monitors or video display terminals (VDTs). Some studies have correlated EMF exposure with higher than expected miscarriage rates; others have found no such correlation. Epidemiologic studies have revealed no evidence of an association between EMF exposure and birth defects in humans. Several studies looked at the overall health of high-voltage electrical workers, and a few looked at the incidence of suicide or depression in people living near transmission lines. Results of these studies have been mixed. Some studies have also investigated the possibility that certain sensitive individuals may experience allergic-type reactions to EMFs, known as 'electrosensitivity'. One preliminary report released in 1994 has suggested a possible link between occupational EMF exposure and increased incidence of Alzheimer's disease. This study also found a higher incidence of Alzheimer's disease among tailors and dressmakers. Source: Infoventures
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