Archive-name: powerlines-cancer-FAQ/part3
Last-modified: 1994/7/4
Version: 2.6
Maintainer: jmoulder@its.mcw.edu

FAQs on Power-Frequency Fields and Cancer (Q&A, Part 2 of 3)

16) Do laboratory studies indicate that power-frequency fields can cause
cancer?

Carcinogens, agents that cause cancer, can be either genotoxic or
epigenetic (in older terminology these were called initiators and
promoters).  Genotoxic agents (genotoxins, initiators) can directly damage
the genetic material of cells.  Genotoxins often affect many types of
cells, and may cause more than one kind of cancer. Genotoxins generally do
not have thresholds for their effect; in other words, as the dose of the
genotoxin is lowered the risk gets smaller, but it may never goes away.  

An epigenetic agent is something that increases the probability that a
genotoxin will damage the genetic material of cells or that a genotoxin
will cause cancer.  Promoters are a particular kind of epigenetic agent
that increase the cancer risk in animals already exposed to a genotoxic
carcinogen.  Epigenetic agents (including promoters) usually affect only
certain types of cells, and may cause only certain types of cancer. 
Epigenetic agents generally have thresholds for their effect; in other
words, as the dose of an epigenetic agent is lowered a level is reached at
which there is no risk. 

16A) Are power-frequency fields genotoxic? 

There are many approaches to measuring genotoxicity.  Whole-organism
exposure studies can be used to see whether exposure causes cancer or
causes mutations.  Cellular studies can be done to detect DNA or
chromosomal damage.  

Very few whole-organism exposure studies have been published (see Loscher &
Mevissen [K6] for summaries of some of the unpublished work).  Bellossi et
al [G13] exposed leukemia-prone mice for 5 generations and found no effect
on leukemia rates; however, since the study used 12 and 460 Hz pulsed
fields at 60 G (6 mT), the relevance of this to power-frequency fields is
unclear.  Otaka et al [G19] showed that power-frequency magnetic fields did
not cause mutations in fruit flies.  Rannug et al [G20] found that
power-frequency magnetic fields did not significantly increase the
incidence of skin tumors or leukemia in mice.  Benz et al [G4] conducted a
multi-generation mouse exposure study in 1983-1985 as part of the NY State
Powerlines Project; this study reported no increase in mutations rates,
fertility, or sister chromatid exchanges, but has never been published in
the peer-reviewed literature.

Published laboratory studies have reported that power-frequency magnetic
fields do not cause DNA strand breaks [G5,G9,G17], chromosome aberrations
[G1,G7,G16], sister chromatid exchanges [G2,G7,G11,G21], micronuclei
formation [G11], or mutations [G3,G16,G18].

Many of the above laboratory studies also examined power-frequency
electrical fields and combination of power-frequency electrical and
magnetic fields [G1,G2,G5,G9,G11,G17].  As with the studies of magnetic
fields alone, the studies of electrical fields and combined fields showed
no evidence of genotoxicity.

There are two published reports of genotoxicity.  Khalil & Qassem [G12]
reported that a 10.5 G (1.05 mT) pulsed field caused chromosome
aberrations.  Nordenson et al [E4] reported that switchyard workers exposed
to spark discharges had an increased rate of chromosomal defects, but
Bauchinger et al [E2] found no such increase in chromosomal defects in a
similar study.

16B) Are power-frequency magnetic fields cancer promoters? 

Epigenetic agents influence the development of cancer without directly
damaging the genetic material.  Promoters are a specific class of such
epigenetic agents.  In a promotion test, animals are exposed to a known
genotoxin at a dose that will cause cancer in some, but not all animals. 
Another set of animals are exposed to the genotoxin, plus another agent. 
If the agent plus the genotoxin results in more cancers than that seen for
the genotoxin alone, then that agent is a promoter.  It has been suggested
that power-frequency EMFs could promote cancer [L2].

Published studies have reported that power-frequency magnetic fields do not
promote chemically-induced skin cancer [G10,G15,G20,G27,G29] or
chemically-induced liver cancers [G22,G25].  For chemically-induced breast
cancer, two published study have reported promotion [G14,G23], but two
others have not found promotion [G24,G28].  Interpretation of the breast
cancer promotion data is complicated by the fact that one of the positive
studies [G14] has been published only in preliminary form, and also reports
that a static magnetic field of less than the intensity of the earth's
magnetic fields can promote chemically induced-breast cancer.

16C) Do power-frequency magnetic fields enhance the effects of other
genotoxic agents?
 
There are some types of studies that are relevant to the carcinogenic
potential of agents, but that are neither classic genotoxicity nor
promotion tests. The most common of these are cellular studies that test
whether an agent enhances the genotoxic activity of a known genotoxin;
these studies could be regarded as the cellular equivalent of a promotion
study.

Published studies have reported that power-frequency magnetic fields do not
enhance the mutagenic effects of known genotoxins [G3], and do not inhibit
the repair of DNA damage induced by ionizing [G8,G9] or UV [G16] radiation.

One study [G7] has reported that power-frequency fields may increase the
frequency of sister chromatid exchanges induced by known genotoxins.

17) Do laboratory studies indicate that power-frequency fields have any
biological effects that might be relevant to cancer?

There are biological effects other than genotoxicity and promotion that
might be related to cancer.  In particular, agents that have dramatic
effects of cell growth, on the function of the immune system, or on hormone
balances might contribute to cancer without meeting the classic definitions
of genotoxicity or promotion.  

17A) How do laboratory studies of the effects of power-frequency fields on
cell growth relate to the question of cancer risk?

There are substances (called mitogens) that cause non-growing normal cells
to start growing.  Some mitogens appear to be carcinogens.  There have been
numerous studies of the effects of power-frequency fields on cell growth
(proliferation) and tumor growth (progression). Most recent studies of the
effects of power-frequency magnetic fields on cancer growth have shown no
effect [G6,G10,H3], but one has reported that a 20 G (2 mT) enhanced tumor
growth [G15].  Most recent studies of effects of power-frequency magnetic
fields on cell growth have also shown no effect [G1,G11,G17,G21,H2,H8,H9],
but some have shown increased [G7] or decreased [G12] cell growth after
exposure to intense (greater than 10 G, 1 mT) fields.  With one
controversial exception [H1] there have been no reported effects on
proliferation or progression for fields below 2000 mG (200 microT).

17B) How do laboratory studies of the effects of power-frequency fields on
immune function relate to the question of cancer risk?

In the early 1970s there was speculation that damage to the immune system
had a major role in preventing the development of cancer; this theory was
known as the immune surveillance hypothesis [E3,E7].  Subsequent studies
have shown that this hypothesis is not generally valid [E3,E6,E7]. 
Suppression of the immune system in animals and humans is associated with
increased rates of only certain types of cancer, particularly lymphomas
[E6,E7].  Immune suppression has not been associated with an excess
incidence of leukemia, brain cancer or breast cancer in either animals or
humans [E3,E6,E7].  

Some studies have shown that power-frequency fields can have effects on
cells of the immune system [K2], but no studies have shown the type or
magnitude of immune suppression that is associated with an increased
incidence of lymphomas.  

17C) How do laboratory studies of the effects of power-frequency fields on
the pineal gland and melatonin relate to the question of cancer risk?

It has also been suggested that power-frequency EM fields might suppress
the production of the hormone melatonin, and that melatonin has
"cancer-preventive" activity [H7,H8,L3].  This is still highly speculative.
 

There have been a number of reports that electrical fields and static
magnetic fields can affect melatonin production [H7], but studies using
power-frequency magnetic fields have not shown reproducible effects.  Kato
et al [H10] reported that exposure to circularly-polarized power-frequency
fields of 10-2500 mG (1-250 microT) caused a small decrease melatonin
production in rats, but that lower-intensity fields [H10] and vertically-
or horizontally-polarized power-frequency fields [H13] had no effect. 
Loscher et al [G28] reported that 3-10 mG (0.3-1.0 microT) power-frequency
fields caused a small decrease in melatonin production in mice, but that
this decrease did not lead to promotion of chemically-induced mammary
tumors.  Lee et al [H11] reported that exposure to a 500 kV transmission
line field (40 mG, 4 microT, 6 kV/m) had no effect on melatonin levels in
sheep.  

The second component of the powerline-melatonin-cancer hypothesis, that a
decrease in melatonin levels will lead to an increase in cancer, is also
unproven.  While there is some evidence that melatonin has activity against
transplanted and chemically-induced breast tumors in rats, there is little
evidence that melatonin affects other types of cancer in animals, or that
it has any effect on breast or other types of cancer in humans.  

18) Do power-frequency fields show any reproducible biological effects in
laboratory studies?

While the laboratory evidence does not suggest a link between
power-frequency magnetic fields and cancer, numerous studies have reported
that these fields do have "bioeffects", particularly at high field strength
[H4,H6,K1,K2].  Power-frequency fields intense enough to induce electrical
currents in excess of those that occur naturally (above 5 G, 500 microT,
see Question 8) have shown reproducible effects, including effects on
humans [K1]. 
    
18A)  Do power-frequency fields of the intensity encountered in
occupational and residential settings show reproducible biological effects?
 
If a reproducible biological effect is defined as one that has been
reported in the peer-reviewed literature by more than one laboratory,
without contradictory data appearing elsewhere; then there may be no
reproducible effects below about 2 G (200 microT).  While there are reports
of effects for fields as low as about 5 mG (0.5 microT), few, if any, of
these reports have been validated.  

The lack of validation of the laboratory studies is due to many factors. 
First, many reports on the biological effects of power-frequency fields
have never been published in the peer-reviewed literature, and cannot be
scientifically evaluated.  Second, no attempts have ever been made to
replicate many of the published reports of biological effects; and one
positive report, standing in isolation, is hard to evaluate.  Third, when
attempts have been made to replicate some of the published studies, these
replications have often failed to show the effect [H5,H2,H12].  Lastly, the
investigators in this field use a wide variety of biological systems,
endpoints, and exposure conditions, which makes studies extremely hard to
compare and evaluate.

18B)  Are there known mechanisms by which power-frequency fields of the
intensity encountered in occupational and residential settings could cause
biological effects?

The known biological mechanisms through which intense (greater than 5 G,
500 microT) power-frequency magnetic fields cause biological effects are
not relevant to fields below about 500 mG (50 microT).  The currents
induced in the body by fields of less than 500 mG (50 microT) are similar
to, but much weaker than, the currents that occur naturally [F2].  The
currents induced by a 50 mG (5 microT) are less than those induced in the
body by walking through the Earths static magnetic field [F2].  Thus, as
emphatically pointed out by Adair [F2,F8], if weak power-frequency magnetic
fields do have biological effects, they are not mediated by induced
currents.

It has been suggested that power-frequency magnetic fields could cause
biological effects by acting directly on magnetic biological material [F3],
but analysis of the biophysics indicates that this would require
power-frequency fields of at least 50 mG (5 microT) [F3,F8].

Some of the biophysical constraints on possible mechanisms for biological
effects of weak power-frequency magnetic fields could be overcome is there
were resonance mechanisms that could make cells (or organisms) uniquely
sensitive to power-frequency fields [F1,F8].  Several such resonance
mechanisms have been proposed, but none have survived scientific scrutiny
[F1,F8,H5,H2,H12].  There are also severe incompatibilities between known
biophysical characteristics of cells and the conditions required for such
resonances [F8].

Thus if power-frequency fields below 50 mG (5 microT) do actually have
biological effects, the mechanisms must be found, in Adairs [F2] words:
outside the scope of conventional physics.  

19) What about the "new epidemiological studies" showing a link between
power frequency fields and cancer?

New studies, particularly epidemiological studies, appear frequently.  When
these studies show "positive" effects they generate considerable media
coverage.  When they fail to show "positive" effects they are generally
ignored.  This section will cover the more recent (1993 and 1994) studies
in some detail.

19A) What about the new "Swedish" study showing a link between power lines
and cancer?

There are new residential exposure studies from Sweden [C13,C18], Denmark
[C16], Finland [C15] and the Netherlands [C17].  The published studies are
considerably more cautious in their interpretations of the data than were
the unpublished preliminary reports and the earlier press reports.

The authors of the Scandinavian childhood cancer studies [C15,C16,C18] have
produced a collaborative meta-analysis of their data [B5].  The RRs
(Question 13) from this meta-analysis are shown below in comparison to
meta-analysis of the prior studies [B3,B4]. 
  Childhood leukemia, Scand:   2.1 (1.1-4.1);  prior: 1.3 (0.8-2.1)
  Childhood lymphoma, Scand:   1.0 (0.3-3.7);  prior: none
  Childhood CNS cancer, Scand: 1.5 (0.7-3.2);  prior: 2.4 (1.7-3.5)
  All childhood cancer, Scand: 1.3 (0.9-2.1);  prior: 1.6 (1.3-1.9)

- Fleychting & Ahlbom [C13,C18].  A case-control study of everyone who
lived within 300 m (1000 ft) of high-voltage powerlines between '60 and
'85.  For children all types of tumors were analyzed; for adults only
leukemia and brain tumors were studied.  Exposure was assessed by spot
measurements, calculated retrospective assessments, and distance from power
lines.  No increased overall cancer incidence was found in either children
or adults, for any definition of exposure.  An increased incidence of
leukemia (but not other cancers) was found in children for calculated
fields over 2 mG (0.2 microT) at the time of diagnosis, and for residence
within 50 m (150 ft) of the power line.  The increased incidence of
leukemia is found only in one-family homes.  The retrospective fields
calculations do not take into account sources other the transmission lines.
 No significant elevation in cancer incidence was found for measured
fields.  
 
- Verkasalo et al [C15].  A cohort study of cancer in children in Finland
living within 500 m (1500 ft) of high-voltage lines.  Only calculated
retrospective fields were used to define exposure.  The calculated fields
are based only on lines of 110 kV and above, and do not take into account
fields from other sources. Both average fields and cumulative fields
(microT - years) were used as exposure metrics.  The total incidence of
childhood cancer was not significantly elevated for average exposure above
0.20 microT (2 mG), or for cumulative exposure above 0.50 microT-years (5
mG-years).  A significant excess incidence of brain cancer was found in
boys; the excess was due entirely to one exposed boy who developed three
independent brain tumors.  No significant increase in incidence was found
for brain tumors in girls or for leukemia, lymphomas or other cancers in
either sex.

- Olsen and Nielson [C16].  A case-control study based on all childhood
leukemia, brain tumors and lymphomas diagnosed in Denmark between '68 and
'86.  Exposure was assessed on the basis of calculated fields over the
period from conception to diagnosis.  No overall increase in cancer was
found when 0.25 microT (2.5 mG) was used as the cut-off point to define
exposure (as specified in the study design).  After the data were analyzed,
it was found that the overall incidence of childhood cancer was
significantly elevated if 0.40 microT (4 mG) was used as the cut-off point.
 No significant increase was found for leukemia or brain cancer incidence
for any cut-off point.  A significant increase in lymphoma was found for
the 0.10 microT cut-off point but not for higher cut-off points.

-Schreiber et al [C17].  A retrospective cohort study of people in an urban
area in the Netherlands.  People were considered exposed if they lived
within 100 meters of transmission equipment (150 kV lines plus a
substation).  Fields in the "exposed" group were 1-11 mG (0.1-1.1 microT),
fields in the "unexposed" group were 0.2-1.5 mG (0.02-0.15 microT).  The
total cancer incidence in the exposed group was insignificantly less than
that in the general Dutch population.  No cases of leukemia or brain cancer
were seen in the "exposed" group.  

19B) What about the new "Swedish" study showing a link between occupational
exposure to power-frequency fields and cancer?

There are new occupational studies from Sweden [D12], Denmark [D14], Norway
[D16], Canada [D15], and the United States [D11,D13].  The published
studies are considerably more cautious in their interpretations of the data
than were the unpublished preliminary reports and the earlier press
reports.

-Floderus et al [D14].  A case-control study of leukemia and brain tumors
in occupationally-exposed men who were 20-64 years of age in '80.  Exposure
calculations were based on the job held longest during the 10-year period
prior to diagnosis.  Many measurements were taken using a person whose job
was most similar to that of the person in the study. About two-thirds of
the subjects in the study could be assessed in this manner.  A significant
elevation in incidence was found for leukemia, but not for brain cancer.

- Guenel et al [D14].  A case-control study based on all cancer in employed
Danes between '70 and '87.  Each occupation-industry combination was coded
on the basis of supposed 50-Hz magnetic field exposure.  No significant
increases were seen for breast cancer, malignant lymphomas or brain tumors.
 Leukemia incidence was significantly elevated among men in the highest
exposure category; women in similar exposure categories showed no increase
in leukemia. 

- Tynes et al [D16].  Case-control study of workers on electrical (16.67
Hz) and non-electrical railroads in Norway.  Analysis showed no significant
excess of leukemia or brain cancer, and no significant trend for either
magnetic or electrical fields.  On the electrified railroads fields
averaged 19.7 mT (197 mG), and 0.8 kV/m.  Cumulative exposures were as high
as 3000 mT-years (30 G-yrs) and 25 kV/m-yrs.

- Theriault et al [D15.  Case-control study of electric utility workers in
France and Canada.  Exposure to magnetic fields were estimated from
measurements of current exposure of workers performing similar tasks.  No
association with magnetic fields was observed for overall cancer or for any
of the other 29 cancer types studied, including melanoma, overall leukemia,
brain cancer or male breast cancer.  Workers with cumulative exposure above
3.1 microT-years (31 mG-years) had a significantly higher incidence of
acute non-lymphocytic and acute myeloid leukemia, there were no clear
dose-response trends.  

- Matanoski et al [D11].  Case-control study of telephone company workers
in New York, with exposure defined by job titles plus some retrospective
measurements.  The incidence of leukemia was increased, but not
significantly so, in workers with higher exposures to magnetic fields.  The
authors interpret their data as showing higher risk with increasing
exposure, but the trend does not appear to be statistically significant.

- Sahl et al [D13].  Cohort plus nested case-control of electrical utility
workers in California.  Dosimetry was done on selected workers. 
Electricians had the highest exposures, with a time-weighted mean of 30 mG
(3 microT).  Neither cohort nor case-control analysis showed a significant
excess of total cancer, leukemia, brain cancer or lymphoma.  No significant
dose-response trend was found for any cancers.
 
19C) What about the new studies showing a link between electrical
occupation and breast cancer?

There are some laboratory studies [G14,G23] that suggest that
power-frequency fields might promote chemically-induced breast cancer (see
Question 16B), and a biological mechanism has been proposed that could
explain such a connection (see Question 17C).  However, there is relatively
little epidemiological support for such a connection.

McDowall et al [C4] found no excess female breast cancer (and no male
breast cancer at all) in adults living near transmission lines or
substations.  Vena et al [C12] found no excess breast cancer in women who
used electric blankets.  Tynes & Anderson [D4] and Demers [D5] both
reported a significantly elevated incidence of male breast cancer in
electrical workers.  Matanoski et al [D6] and Loomis et al [D7] also
reported an excess incidence of male breast cancer in electrical workers,
but in neither case was the increase statistically significant.  More
recently, studies by Theriault et al [D15], Rosenbaum et al [D17] and
Guenel et al [D14] have found no excess breast cancer in electrical
workers.

Recently, Loomis et al [D18,D19] reported a significantly elevated
incidence of female breast cancer in occupations with presumed exposure to
power-frequency fields.  In occupations with "potential exposure" to
power-frequency fields there was no increased incidence of breast cancer. 
The occupations that showed an excess incidence of breast cancer were
male-dominated and the ones that did not were largely female-dominated.
 The authors note that breast cancer mortality is known to be elevated
among women in professional and technical jobs in general.  This elevation
is related to the fact that women working in male-dominated jobs tend to
have reproductive histories (for example, no pregnancies, delayed
child-bearing, not breast-feeding) that increase their risk for breast
cancer.  

20) What criteria do scientists use to evaluate all the confusing and
contradictory laboratory and epidemiological studies of power-frequency
magnetic fields and cancer?

There are certain widely accepted criteria that are weighed when assessing 
epidemiological and laboratory studies of agents that may pose human health
risks.  These are often called the "Hill criteria" [E1].  Under the Hill
criteria one examines the strength (Question 20A) and consistency (Question
20B) of the association between exposure and risk, the evidence for a
dose-response relationship (Question 20C), the laboratory evidence
(Question 20D), and the biological plausibility (Question 20E).  

The Hill criteria must be applied with caution.  First, when employing the
Hill criteria it is necessary to examine the entire published literature;
it is not acceptable to pick out only those reports that support the
existence of a health hazard.  Second, it is necessary to directly review
the important source documents; it is not safe to base judgments solely on
academic or regulatory reviews.  Third, satisfying the individual criteria
is not a yes-no matter; support for a criterion can be strong, moderate,
weak, or non-existent.  Lastly, 
the Hill criteria must be viewed as a whole; no individual criterion is
either necessary or sufficient for concluding that there is a causal
relationship between exposure to an agent and a disease.

Overall, application of the Hill criteria shows that the current evidence
for a connection between power-frequency fields and cancer is weak, because
of the weakness and inconsistencies in the epidemiological studies,
combined with the lack of a dose-response relationship in the human
studies, and the largely unsupportive laboratory studies.  A detailed
evaluation of the criteria follows.

20A) Criterion One: How strong is the association between exposure to
power-frequency fields and the risk of cancer?

The first Hill criterion is the *strength of the association* between
exposure and risk.  That is, is there a clear risk associated with
exposure?  A strong association is one with a RR (Question 13) of 5 or
more.  Tobacco smoking, for example, shows a RR for lung cancer 10-30 times
that of non-smokers.  

Most of the positive power-frequency studies have RRs of less than two. 
The leukemia studies as a group have RRs of 1.1-1.3, while the brain cancer
studies as a group have RRs of about 1.3-1.5.  This is only a weak
association.

20B) Criterion Two: How consistent are the studies of associations between
exposure to power-frequency fields and the risk of cancer?

The second Hill criterion is the *consistency* of the studies.  That is, do
most studies show about the same risk for the same disease?  Using the same
smoking example, essentially all studies of smoking and cancer showed an
increased risk for lung and head-and-neck cancers. 

Many power-frequency studies show statistically significant risks for some
types of cancers and some types of exposures, but many do not.  Even the
positive studies are inconsistent with each other.  For example, while a
recent Swedish study [C18] shows an increased incidence of childhood
leukemia for one measure of exposure, it contradicts prior studies that
showed an increase in brain cancer [B3,B4], and a parallel Danish study
[D14] shows an increase in childhood lymphomas, but not in leukemia.  

Many of the studies are internally inconsistent.  For example, where a
recent Swedish study [C18] shows an increase for childhood leukemia, it
shows no overall increase in childhood cancer.  Since leukemia account for
about one-third of all childhood cancer, this implies that the rates of
other types of cancer were decreased; an examination of the data indicates
that this is true.  In summary, few studies show the same positive result,
so that the consistency is weak.

20C) Criterion Three: Is there a dose-response relationship between
exposure to power-frequency fields and the risk of cancer?

The third Hill criterion is the evidence for a *dose-response
relationship*.  That is, does risk increase when the exposure increases? 
Again, the more a person smokes, the higher the risk of lung cancer.

No published power-frequency exposure study has shown a dose-response
relationship between measured fields and cancer rates, or between distances
from transmission lines and cancer rates.  The lack of a relationship
between exposure and increased cancer incidence is a major reason why most
scientists are skeptical about the significance of the epidemiology.

Not all relationships between dose and risk can be described by simple
linear no-threshold dose-response curves where risk is strictly
proportional to risk.  There are known examples of dose-response
relationships that have thresholds, that are non-linear, or that have
plateaus.  For example, the incidence of cancer induced by ionizing
radiation in rodents rises with dose, but only up to a certain point;
beyond that point the incidence plateaus or even drops.  Without an
understanding of the mechanisms connecting dose and effect it is impossible
to predict the shape, let alone the magnitude of the dose-response
relationship.

20D) Criterion Four: Is there laboratory evidence for an association
between exposure to power-frequency fields and the risk of cancer?

The fourth Hill criterion is whether there is *laboratory evidence*
suggesting that there is a risk associated with such exposure? 
Epidemiological associations are greatly strengthened when there is
laboratory evidence for a risk.  When the US Surgeon General first stated
that smoking caused lung cancer, the laboratory evidence was ambiguous.  It
was known that cigarette smoke and tobacco contained carcinogens, but no
one had been able to make lab animals get cancer by smoking (mostly because
it is hard to convince animals to smoke).  Currently the laboratory
evidence linking cancer and smoking is much stronger.

Power-frequency fields show little evidence of the type of effects on
cells, tissues or animals that point towards their being a cause of cancer,
or to their contributing to cancer (Question 16).

20E) Criterion Five: Are there plausible biological mechanisms that suggest
an association between exposure to power-frequency fields and the risk of
cancer?

The fifth Hill criterion is whether there are *plausible biological
mechanisms* that suggest that there should be a risk?  When it is
understood how something causes disease, it is much easier to interpret
ambiguous epidemiology.  For smoking, while the direct laboratory evidence
connecting smoking and cancer was weak at the time of the Surgeon Generals
report, the association was highly plausible because there were known
cancer-causing agents in tobacco smoke.

From what is known of power-frequency fields and their effects on
biological systems there is no reason to even suspect that they pose a risk
to people at the exposure levels associated with the generation and
distribution of electricity (see Questions 16,17,18).

Copyright (C) by John Moulder
end: powerlines-cancer-FAQ/part3
