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Extremely Low Frequency Field Exposure & Childhood Leukemia

CancerNet from the National Cancer Institute
CANCER FACTS
National Cancer Institute
National Institutes of Health

Extremely Low Frequency Field Exposure & Childhood Leukemia

Collaborative Study of Extremely-Low-Frequency Electromagnetic Field Exposure & Childhood Leukemia

The National Cancer Institute (NCI) and the Children's Cancer Group (CCG) are
collaborating on a large-scale investigation to determine whether exposures to
extremely-low-frequency (ELF) electromagnetic fields contribute to the
development of acute lymphocytic leukemia (ALL) in children under age 15.  ALL
accounts for 85 percent of all childhood leukemias in the United States.

ELF electromagnetic fields are the electric and magnetic fields created by
electric charges in the 60-hertz (60 cycles per second) alternating current
supplied to U.S. households.

The 5-year study, directed by NCI's Epidemiology and Biostatistics Program, was
initiated in September 1989 because of public concern and a need for more precise
epidemiologic data.  It is part of a larger CCG investigation evaluating the risk
of ALL associated with a wide range of factors, such as prenatal exposure to
x-rays, childhood and maternal diseases, maternal drug use, maternal smoking,
parental occupations, household chemical exposures, and family genetic histories.

For the ELF field evaluation, 600 children with ALL and 600 matched controls are
being selected from the 1,800 cases and 1,800 controls (the latter identified by
random-digit telephone dialing) who are participating in the comprehensive CCG
study.  The subjects, all under age 15, will include residents of 11 states:  
Illinois, Indiana, Iowa, Kentucky, Maryland, Michigan, Minnesota, New Jersey,
Ohio, Pennsylvania, and Wisconsin.

A dosimetry study was conducted to determine the best way to estimate children's
ELF exposure levels.  Children under age 9 wore monitors that recorded all ELF
exposures during a 24-hour period.  When results were compared with ELF field
measurements made in homes, schools, and day care centers, the home measurements
were found to correlate closely with actual cumulative ELF exposures, while
school and day care center measurements contributed little to the overall ELF
exposure history.  Based on these findings, several types of home measurements
were selected for use in the main ELF field study to characterize exposures for
all cases and controls.

The relationship between ELF radiation (from both household sources and electric
power lines) and ALL is being examined by:


      -     Measuring ELF radiation levels in four rooms in current and former
            homes of children with leukemia and matched controls;

      -     Interviewing parents about their children's ELF exposures (including
            prenatal exposures) from electrical appliances;

      -     Diagramming the location, type, and size of external power lines
            near residences;

      -     Measuring the earth's magnetic field in two rooms to determine its
            possible influence on ELF field measurements;

      -     Examining seasonal variability in ELF radiation levels within
            selected homes over a 1-year period;

      -     Determining whether electric meter readings and utility company
            records can be used to approximate ELF radiation measurements in a
            home; and

      -     Replicating the personal ELF radiation dosimetry study on selected
            control subjects in both younger (0-8 years) and older (9-14 years)
            age groups.

Data on individual subjects will be used to estimate the amount of ELF exposure
prenatally and throughout life.  Estimates will be made for both the children who
developed ALL and their matched controls.  It will then be determined whether ELF
exposure increases the risk of childhood ALL.  This study will provide one of the
first comprehensive and complete measures of ELF exposures in children's
residences.

In summary, children with newly diagnosed ALL and matched controls will have ELF
field measurements made in current and former homes.  For children with leukemia,
measurements will be obtained closer to their date of diagnosis than was possible
in previous studies.  The possible role of ELF magnetic field exposures will be
evaluated as part of a large-scale, comprehensive study of virtually all known
or suspected causes of childhood ALL.  Results from the study should be available
in 1995.
                                     # # #

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                            Questions and Answers  

                Collaborative Study of Extremely-Low-Frequency
                   Radiation Exposure and Childhood Leukemia


1.    What are extremely-low-frequency (ELF) electromagnetic fields?

      The electric and magnetic fields created by electric charges in 60-hertz
      alternating current are commonly referred to as extremely-low-frequency
      electromagnetic fields.  Electric fields result from the strength of the
      charge, and magnetic fields arise from charge motion.

      An electric device that is plugged into a wall socket and activated
      generates both electric and magnetic fields.  If the device is turned off
      and left plugged in, only the electric field remains, because no charges
      are in motion.  The intensity of both kinds of fields drops off as
      distance from the source increases.

      ELF electromagnetic fields are considered nonionizing radiation, radiation
      that does not possess enough energy to remove electrons from atoms.  
      Therefore, they cannot alter genes.  The energy in ionizing radiation,
      such as x-rays and gamma rays, can break atomic bonds and cause
      chromosomal changes.  ELF fields also differ greatly from microwaves,
      which are used to operate microwave ovens and radar:  microwaves are
      nonionizing radiation of much higher frequencies (3 billion to 30 billion
      hertz).  Findings on the biological effects of one form of radiation
      cannot necessarily be generalized to other forms of radiation of different
      wavelengths.


2.    Have ELF fields been shown to cause or promote cancer?

      A small number of cell culture studies have indicated that ELF fields may
      cause biological effects in living tissues, such as interference with
      protein synthesis.  However, these biological effects have not been proven
      hazardous.  There is still no evidence that ELF fields cause or promote
      cancerous transformation of normal cells.

      Studies of laboratory animals exposed to ELF radiation have not shown any
      increased risk of cancer.  Occupational studies of electrical workers have
      suggested an association with cancers, particularly leukemias and brain
      tumors.  However, these studies are difficult to interpret because
      electrical workers are often exposed to chemicals, solvents, and other
      carcinogens.

      For example, a National Cancer Institute (NCI) case-control study of brain
      tumors found an elevated risk among persons who worked in the electrical
      and electronics industry.  Risk of brain tumors rose with length of
      employment in the manufacturing or repair of electronic equipment but not
      among workers exposed to electric and magnetic fields.


3.    What have previous epidemiologic studies of ELF fields and cancer shown?

      Human epidemiologic studies of ELF fields and cancer have been
      inconsistent and inconclusive.  Findings from studies in Colorado and
      Sweden, which suggested a small increase of cancer in children and adults
      living near high-current power lines, were not confirmed in similar
      studies in Rhode Island, Washington, and England.

      A 1987 case-control study in Denver suggested a significant risk of
      childhood cancer associated with living near high-voltage power lines.  
      However, the association was made using wire code configurations (diagrams
      showing increasing levels of current-carrying capacity) as a surrogate for
      ELF exposure levels.  No consistent risk for childhood cancer was seen in
      homes where actual measurements were made.  Similar findings were reported
      in a 1991 case-control study of childhood leukemia in Los Angeles.

      A study of leukemia in adults conducted by the University of Southern
      California did not find any connection between the occurrence of leukemia
      and the use of electric blankets.  Findings on the relationship between
      appliance use and childhood cancer have been inconsistent.

      Two comprehensive reviews published in 1992 by the Oak Ridge Associated
      Universities and the National Radiological Protection Board (United
      Kingdom) on the health effects of ELF electromagnetic fields both
      concluded that the human data to date provide no firm evidence of a
      carcinogenic hazard from ELF exposure.


4.    What advantages does the NCI-Children's Cancer Group (CCG) collaborative
      study have over previous examinations of ELF fields and childhood
      leukemia?

      ūThe study focuses on newly diagnosed cases.  Previous studies have
      frequently involved ELF exposure estimates made as long as 20 years after
      the diagnosis of leukemia.  Because families of the cases and controls had
      in many cases moved, many relevant homes were not measured for ELF
      radiation levels, and few opportunities existed for interviewing parents
      about other causal factors (such as pesticide exposures or medical
      x-rays).  The NCI-CCG study uses a population of newly diagnosed
      (incident) ALL cases, allowing the researchers to make measurements and
      estimates of ELF exposures soon after the date of leukemia onset.  
      Extensive ELF field measurements are obtained within and immediately
      outside residences.  Parents are asked detailed questions about their
      child's lifetime appliance exposure and daily environment.

      ūThe study includes a strong measurement component.  Previous studies have
      utilized incomplete ELF radiation measurements (such as measurements in
      only one home), surrogates for measurements, or no measurements at all.  
      The NCI-CCG study includes ELF field assessment in nearly all current and
      former residences of subjects. Measurements used in previous studies, such
      as wire code configurations and the earth's magnetic field, are also
      included.

      ūThe study benefits from being part of a larger investigation.  Previous
      studies of ELF radiation have varied greatly in their sample selection,
      methodologies, and analyses.  Data interpretations, comparisons of
      results, and extensions of findings to larger populations are difficult.

      The NCI-CCG ELF radiation study utilizes leukemia cases and matched
      controls from 11 states participating in the nationwide CCG study.  Like
      all subjects in the large-scale investigation, they are being evaluated
      for many other exposures and factors suspected of being associated with
      childhood leukemia.  This will allow ELF exposure data to be analyzed with
      respect to data collected for other risk factors.  For example, if a child
      with leukemia has been heavily exposed to ELF radiation and the mother
      received x-rays while pregnant, the researchers will adjust for the x-ray
      factor.  The result will be a more accurate evaluation of the possible
      relationship between ELF and that child's leukemia.


5.    How was the study design approved?  How will the results be evaluated?

      The design of the study (protocol) was critically evaluated by internal
      committees in NCI's Epidemiology and Biostatistics Program.  Because of
      the importance of clarifying any potential health hazards associated with
      ELF exposure from power lines near residences and from electrical
      appliances and wiring inside homes, a special advisory group was
      established to also review and approve the final protocol, help monitor
      the study, and evaluate the results.  The advisory group consists of
      selected members of the NCI's Division of Cancer Etiology's Board of
      Scientific Counselors and other scientists with expertise in this area.

      In addition to the normal NCI internal peer review requirements for
      approval of scientific studies before they are submitted to journals for
      publication, the advisory group will review and comment upon the
      scientific validity of the final report.


6.    What is the Children's Cancer Group?

      The CCG is an NCI-supported, multicenter network of pediatric oncologists,
      epidemiologists, and other cancer researchers from 38 institutions and
      affiliated hospitals throughout the United States.  The CCG Operations
      Center is located at the National Childhood Cancer Foundation in Arcadia,
      California.     
     

Date Last Modified: 12/92

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