ARPANSA - Australian Radiation Protection and Nuclear Safety Agency

An epidemiological study reported in 1997 by Linet and colleagues in the New England Journal of Medicine (a prestigious medical journal) concluded that there was no significant excess risk of acute lymphoblastic leukemia (ALL) associated with magnetic field exposures of 0.2 µT or greater.

Background

In 1979 Werthiemer and Leper published the first epidemiological study which suggested that proximity to powerline electromagnetic fields is associated with an increase in leukemia. Since that time there have been several other studies which have indicated either no association or a weak association between powerlines and cancer. The present work investigates the incidence of ALL which is the most common childhood cancer and has been increasing in incidence for the past 20 years. Since this is concomitant with increased electricity usage the possibility of an association exists.

Epidemiology

Analytical epidemiological studies can be carried out using one of two methods. In the first method, referred to as a cohort study, a group of people exposed to the risk factor under test are compared with a similar group of people who are not so exposed (the control group). The incidence rates of disease in the two groups are then analyzed mathematically to see if there is an excess of disease in the exposed group thus establishing an association. In the second method, called a case-controlled study, a group of people with a disease suspected to be caused by the risk factor under study (the cases), is compared with a similar group of people who do not have the disease (the controls). The data is then analyzed to see if the 'cases' have higher exposure to the risk factor than the 'controls' thereby establishing an association.

It is important in doing these types of studies that the 'control' group be as similar to the 'exposed' or 'cases' group as possible to avoid what are known as confounding errors. For example, a study of the health hazards from drinking alcohol might compare drinkers with non-drinkers. This is likely to lead to an erroneous result because drinkers tend to smoke more than non-drinkers and the health hazard from cigarette smoking would be confused with that from drinking alcohol.

Other errors which occur in these types of studies include measurement of exposures. It is a fairly simple matter to discriminate smokers from non-smokers simply by interview. In the case of exposure to magnetic fields interview is not possible. In studies up to date a surrogate (substitute) for measurement of magnetic field exposure has been used. For example, the 1979 Werthiemer and Leper study which indicated an association between powerline magnetic fields and childhood leukemia used so called 'wire codes' (the distribution patterns of residential powerlines) as an indicator of exposure to magnetic fields. This type of study is subject to criticism because no actual measurement of household exposures are made and no effort is made to see if the neighbouring residents have occupied their homes for a reasonable period.

The Study

The Linet study is of particular importance because the authors have gone to considerable length to remove weaknesses present in previous studies investigating a possible link between powerline magnetic fields and childhood leukemia. This was a case control study comparing 638 children with ALL and 620 controls. The study was therefore quite large and actual measurements of magnetic fields were made. In addition wire codes were assigned to 416 cases and 416 controls so the effect of this surrogate could be determined. This included, in 41 per cent of the cases, wire codes determined at the homes where the mothers resided whilst pregnant.

Conclusion

Linet concluded "our comprehensive case-control investigation did not find significantly increased risks of ALL associated with time-weighted average summary residential magnetic-field measurements or with residence in homes characterized by a high wire-code category during the five years immediately preceding the diagnosis of ALL or during the index pregnancy."

Update

This study has been criticized because it did not strictly comply with the Wertheimer-Leeper wire code and proximity to high voltage power lines as distinct from power lines in general. Other studies which had shown a link with leukemia had used proximity to high voltage power lines. Therefore a>second study has been performed using data for high voltage lines and the distances that subjects were living from these lines were measured.

The study failed to show either an association with distance from the nearest power line (within 40 meters) or with living within 40 m of a high voltage line.

Related Links

The United States National Institute of Environmental Health Sciences (NIEHS) Conclusion on Health Effects of Electric and Magnetic Fields
The Controversy Over Electromagnetic Fields and Possible Adverse Health Effects
Comments on Pooled Analysis Study of Magnetic Fields and Childhood Cancer (childhood leukemia)
Distance of Place of Residence from Dense Traffic; An Alternative to 50Hz Magnetic fields as a Risk Factor for Leukemia and Other Childhood Cancers?
Powerline (Extremely Low Frequency ELF) Electromagnetic Fields and Cancer - The Doll Report

References

Residential Exposure to Magnetic Fields and Acute Lymphoblastic Leukemia in Children
The New England Journal of Medicine
1997, 337:1-44.
M S Linet, E E Hatch, R A Kleinerman, L L Robison, W T Kaune, D R Friedman, R K Severson, C M Haines, C T Hartsock, S Niwa, S Wacholder and R E Tarone

Electrical Wiring Configurations and Childhood Cancer
Am. J. Epidemiol.
1979, 109:273-284.
N Wertheimer and E Leeper

Are Children Living Near High-Voltage Power Lines at Increased Risk of Acute Lymphoblastic Leukemia?
Am. J. Epidemiol.
2000, 151:512-515.
R A Kleinerman, M S Linet, E E Hatch, L L Robison, W T Kaune, S Niwa, S Wacholder and R E Tarone

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