Chapter 15. Do electromagnetic fields cause cancer?

There is debate over whether electric power lines cause cancer. Much of the uncertainty arises because the available data involve correlations.

This chapter is a brief overview of a possible public health hazard - electromagnetic fields, which are produced by the electricity we use. There are two models at issue

• Model 1: electromagnetic fields from residential sources increase cancer rates.
• Model 2: electromagnetic fields from residential sources do not increase cancer rates.

Box 2.1 What is electromagnetic radiation?

Origin of concern

Beginning in the 1960's and the 1970's, evidence arose that intense electromagnetic fields could influence behavior and physiology. No study was particularly conclusive. In all cases, the fields were intense and effects seemed reversible, and the concern was neither about cancer nor about effects from fields of low intensity such as those in the typical neighborhood. But in 1979, epidemiologists Nancy Wertheimer & Ed Leeper reported that childhood leukemia rate in Denver was higher for dwellings "near" a transformer than for dwellings away from a transformer. The result was incredible because it suggested that many of us are exposed to a cancer risk in our own dwellings. There have been at least 6 attempts to repeat Wertheimer and Leeper's epidemiological correlations, and the overall trend continues to be born out (with some inconsistencies); studies appear maybe a couple of times a year now. Overall, it appears that there is a slightly elevated risk of leukemia associated with living near high current transformers and the wires that emanate from them (the risk factor is 1-2). The baseline rate for childhood leukemia is about 1/20,000, so the EMF risk raises it to 1/10,000.

In addition, there appears to be an association of cancer with occupations exposed to high intensity EMF, although the results are inconsistent between studies and even within studies. One study (NY telephone) made an attempt to determine if there was a correlation between cancer and occupations which had varying exposure to the EMF.

Cancer incidence vs. exposure to electromagnetic fields

The occupations are ranked according to exposure and the cancer incidence is indicated. However, this is the only study (of many) showing a possible dose response effect, and even in this case, the results present a heterogeneous array of cancers.

Reasons for being skeptical

If EMFs cause cancer, then we should see an effect of EMFs on biological tissue. There have been attempts to explore possible biological mechanisms that could account for EMF-induced cancer, but most have given negative results.

In determining whether it is reasonable to suppose that electromagnetic fields cause cancer, once needs to consider their energy and intensity. Electromagnetic fields from alternating current are low in energy. The energy of electromagnetic radiation increases with the frequency of radiation. Alternating current cycles at 60 times/second, so its frequency is 60 cycles/second. Visible light has a frequency of 10¹⁴ cycles/second, UV light has a frequency of 10¹⁵-10¹⁶ cycles/second, and X-rays have a frequency of 10¹⁶-10²⁰ cycles/second (g and cosmic rays have even higher frequencies). So the electromagnetic fields (EMFs) of alternating current have only a trivial level of energy compared to X-rays.

In addition to the energy of EM radiation, one needs to consider the intensity. Intensity is the amount of radiation per unit time. For example, a light bulb emits more intensely when it is bright than when it is dim, even though the energy level of individual photons is the same. So even though EMF from alternating current might be too low in energy to produce mutations, high intensity fields might have some biological effects. Here again, however, there would seem to be little reason for concern. Field intensity falls rapidly with distance, so even though the field intensity of various house-hold appliances is high at the source (e.g., the motor in a hair dryer), the field is quite small only a few inches away. And intensities experienced in the household are small relative to the Earth's magnetic field and to the electrical fields generated by our own cells. The only possible cause for concern, therefore is that the man-made fields oscillate, whereas the cells' electrical fields and Earth's magnetic fields do not.

In addition to the fact that the energy and intensity of EMFs does not appear likely to have biological effects, science has also not found any clear biological mechanism by which EMFs can cause cancer. One study showed that EMF suppresses melatonin (hormone) levels. Low melatonin levels are associated with breast and prostrate cancer, but these are not the types of cancer most often related to EMF exposure. Another recent finding suggested that EMF affects calcium uptake by cells. Calcium is associated with cell division. EMF is not associated with mutations in DNA.

Where things stand now

We do not know if EMF causes cancer. More isolated correlations between cancer and EMFs keep cropping up, such as the suggestion that radar "guns" used by police cause cancer (in the police, not in the speeding driver) or that cellular telephones cause brain cancer. Yet the evidence in favor of an EMF cancer connection remains correlational, and there are several additional reasons for doubting the causation:

• 1. There is no readily conceivable physical mechanism (energy levels are too low).
• 2. The initial hints for biochemical evidence do not suggest the types of cancer that are actually observed.
• 3. The increase in electrical usage in society should have been accompanied by a proportional increase in leukemia, but was apparently not.
• 4. There is no obvious dose response.

Nonetheless, there is increasing advocacy of "prudent avoidance" of EMFs: children and pregnant women are advised (by Consumer Reports) to avoid ordinary electric blankets, and people should generally distance themselves from high-EMF electric appliances.