• 05 AUG 11
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    Sage Associates’ comments on the De-Kun Li paper (previous message)

    From Cindy sage:

    Critics of the Li paper on maternal EMF exposures and childhood asthma are quick to dismiss possible consequences of this important new study. One example is the comment of Prof. William Stewart in the UK. We draw his attention to the following published studies.

    “Prof William Stewart, Visiting Professor at University of Southampton and an expert in electromagnetic fields, said the study had “a number of weaknesses”, including the use of meters that measure only AC fields and not the Earth’s DC field. ‘This is important because the biological interactions of pure magnetic fields are very small compared with those of electric fields – so the authors should not describe it as a magnetic field effect at all, or mums-to-be will start to hide from the earth’s 500mG field in magnetically-shielded rooms!”

    Experts criticise study linking magnetic field exposure to asthma risk

    Prof. Stewart’s comments that relate to the earth’s geomagnetic field are not relevant to this discussion, and give a misleading comparison. Humans evolved with the DC geomagnetic fields of the earth.

    The earth’s geomagnetic fields vary from 300 mG to 700 mG (the same as 30 to 70 microtesla or uT) which sound excessively high by comparison to 2 mG in the asthma paper. But humans evolved with DC geomagnetic fields and are adapted to and dependent on them, it is not the same as alternating or AC power frequency fields that are man-made and associated with increased risk of cancers and other diseases.

    “The earth’s geomagnetic (static) field is another source of exposure, but this field is a natural part of the environment under which all life on earth evolved, and is unlike the artificial magnetic field produced by an appliance or PDA. Appliances or PDAs emit ELF signals that contain both intensity and frequency information; it is the combination of these information categories that has been shown to be biologically active at low intensities [Adey, 1992; Liboff, 1992]. The earth’s geomagnetic field intensity can vary from about30 to 70 microtesla (uT) depending on location on the earth’s surface, and this can sound quite high when improperly compared to electric appliances. However, the geo- magnetic field is not comparable to man-made ELF magnetic fields from appliances or PDAs in terms of potential health concerns.”


    Sage C Johansson O Sage SA. 2007. Personal digital assistant (PDA) cell phone units produce elevated extremely-low frequency electromagnetic field emissions. Bioelectromagnetics 28(5) 386-392.

    Sage C Johansson O Sage SA. 2007. Response to Comment on “Personal Digital Assistant (PDA) Cell Phone Units Produce Elevated Extremely-low Frequency Electromagnetic Field Emissions.” Bioelectromagnetics 28(7) 581-582.

    Sage C Johansson O. 2007. Response to comment on “Measuring ELF fields produced by mobile phones and personal digital assistants (PDAs)”. Bioelectromagnetics 28(7)

    It would be more informative for Prof. Stewart to cite average residential exposures for ELF-EMF to compare to these magnetic field levels linked to increased asthma risk for children.

    BioInitiative Report Section 20

    What are Ambient ELF and RF Levels? Average Residential Exposures to ELF (Power Frequency Fields)

    A nation-wide survey in the United States by Zaffanella et al (1993) collected engineering data on sources and levels of 60 Hz electric power magnetic fields that exist inside residences in the United States. Approximately 1000 residences were randomly selected for the survey. The goals were to 1) identify all significant sources of magnetic field, 2) estimate for each source the percentage of residences where magnetic fields exceeded specified levels, 3) to determine the relation between magnetic field and sources and 4) to characterize the field varations in time.

    The median field was identified as 0.5 mG and the average field was 0.9 mG. Thus, this confirms that average residential magnetic fields based on the 1000-home study is less than 1 mG.

    Appliances produce magnetic fields but these diminish rapidly with distance (at 1/R3),

    Power lines generally produce the largest average residential magnetic field when the entire living space of a residence and a 24-hour period are considered. Power line magnetic field exceeds 1 mG in 17%, exceed 2.5 mG in 9.5% and exceed 5 mG in 0.3% of all the residences surveyed.

    Zaffanella (1998) conducted measurements to characterize typical EMF exposure levels in persons living in the United States – a study called the 1000-Person Study. Table A- S.2 shows that about half of all people in the US have EMF exposures at home under 0.75 mG; in bed are 0.48 mg; at school 0.60 mG; at work 0.99 mG; and 0.87 mG is the median EMF exposure for an average 24-hour day.


    BioInitiative Working Group, Cindy Sage and David O. Carpenter, Editors. BioInitiative Report: A Rationale for a Biologically-based Public Exposure Standard for Electromagnetic Fields (ELF and RF) at www.bioinitiative.org, August 31, 2007. 584-585.

    Sage C. Carpenter DO. 2009. Public Health Implications of Wireless Technologies. Pathophysiology 16 (2009) 233–246

    Where there is extended or chronic exposure, magnetic field levels of only 1-2 mG and above have been associated with increased risk of cancer and neurological diseases in many scientific studies and reviews.

    “It is no longer acceptable to build new power lines and electrical facilities that place people in ELF environments that have been associated with an increased risk of adverse health effects, levels generally at 2 mG (0.2 mT) and above.”


    Hardell L Sage C. Biological effect from electromagnetic field exposure and public exposure standards. Biomedicine & Pharmacotherapy 2008;62:104-109. doi:10.1016/j.bipha. 2007.12.004.

    Carpenter DO Sage CL. 2008. Setting Prudent Public Health Policy for Electromagnetic Field Exposures. Reviews on Environmental Health 23(2) 91-117.

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