Power Lines and Childhood Leukemia
ABSTRACT & COMMENTARY
Synopsis: It is unlikely that exposure to the magnetic fields generated by power lines is an etiologic factor in childhood leukemia.
Source: Linet MS, et al. Residential exposure to magnetic fields and acute lymphoblastic leukemia in children. N Engl J Med 1997;337:1-7.
Previous studies reported possible associations between childhood leukemia and residence in the vicinity of high-voltage power lines. The authors, who are participants in the national Children’s Cancer Group (CCG), enrolled 629 children younger than 15 years old who were diagnosed with acute lymphoblastic leukemia (ALL) between 1989 and 1994. A non-leukemic control group was chosen by random digit telephone dialing and were individually matched to the children with ALL according to the first eight digits of the telephone number, age, and race. Trained data collectors, who were blinded to the child’s health status, directly measured low-frequency magnetic fields (30-200 Hz) in the child’s current and any previous residences. Measurements were made for 24 hours in the child’s bedroom. Shorter determinations were made in other rooms of the residence as well as outside of the front door. In 40% of the ALL children, measurements were also made in the home where their mothers resided during the pregnancy of the child. These measurements were usually made within 24 months of diagnosis.
The risk of ALL was not found to be significantly linked to either directly measured magnetic field levels or indirect estimates of possible exposure based upon proximity to high-tension wire lines (wire coding) in either the child’s residence or the mother’s residence during pregnancy.
COMMENT BY HOWARD A. PEARSON, MD, FAAP
More than 2000 children are diagnosed with ALL each year in the United States. The annual incidence of ALL in the United States has increased about 20% over the past two decades.1 The etiology of ALL as well as the reasons for its increasing incidence are largely unknown. There have been several reports that have suggested that living close to high- voltage power lines may cause leukemia in children.2,3 However, in none of the previous studies were direct measurements made of low-frequency electromagnetic fields. Rather, they relied upon proxy estimates of exposure based on distances of residences from power lines and on wiring configurations (so called "wire coding" classification). These estimates were usually done long after the diagnosis. The study by Linet and colleagues goes a long way to address the serious limitations of the previous studies purportedly showing an association between power lines and ALL. Their conclusion, that there is no association, is based on a careful experimental design, large numbers of patients and appropriate controls, careful direct measurements, and expert statistical analysis of their data.
In a somewhat testy editorial accompanying the Linet paper, Edward W. Campion points out that the low-frequency electromagnetic fields associated with power lines are only 10-15% as strong as the Earth’s static magnetic field. In addition, the amount of electromagnetic energy in them is "far below that required to break molecular bonds such as those in DNA." Electromagnetic fields have no reproducible biologic effects at all, except at strengths far beyond those ever found in homes. He essentially says, "Enough is enough; let’s stop spending millions of dollars on unnecessary studies of this sort and get on with the job of finding the true cause or causes of ALL." As convincing as this study appears to be, it is unlikely that the controversy will be laid to rest. As long as there are dedicated conspirators who believe that industrial and military interests are concealing medical facts, and as long as the etiology of ALL remains a mystery, even a precisely designed study with clear-cut negative results is unlikely to be totally accepted. Clusters of ALL are dramatic and capture public attention. However, most do not have a demonstrable biologic etiology. As often pointed out by Robert Miller, MD, a respected pediatric cancer epidemiologist at the National Cancer Institute, "In a disease with the frequency of ALL, clustering is a statistical inevitability."
References
1. Pui C-H. Childhood leukemia. N Engl J Med 1995; 332:1618-1630.
2. Wertheimern N, Leeper E. Electrical wiring configuration and childhood cancer. Am J Epidemiol 1979;109:273-284.
3. Feychting M, Ahlbom A. Magnetic fields and cancer in children residing near Swedish high-voltage power lines. Am J Epidemiol 1993;138:467-481.
4. Campion EW. Power lines, cancer and fear: Clusters of ALL are dramatic and capture public attention. N Engl J Med 1997;337:44-46.
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