Magnetic and Electromagnetic Therapy
By David W. Ramey, DVM
One of the more popular therapies for the treatment of a variety of conditions in human
and veterinary medicine is the application of a magnetic field. The biological effects of low-level magnetic fields have been
studied since the 1500s. The crucial question, however, is whether these effects have any physiological significance. Many
claims have been made for the therapeutic effectiveness of magnetic fields, but are there any good reasons for believing them?
The idea that magnetic therapy could be used to treat disease began in the early 16th
century with the Swiss physician, philosopher, and alchemist Paracelsus, who used magnets to treat epilepsy, diarrhea, and
hemorrhage.1 Magnetic therapy became more popular in the mid-18th century when Franz Mesmer, an Austrian doctor
who also helped begin the fields of hypnotism and psychoanalysis (and from whose name the word "mesmerize" was coined), opened
a popular magnetic healing salon in Paris. The purpose of the salon was to treat the untoward effects of the body's innate
"animal magnetism." In spite of continued condemnation by the scientific community, magnetic therapy became a popular form
of treatment by the lay community.
Over the next few centuries, magnetic therapy developed into a form of quackery. In
1799, Elisha Perkins, a Connecticut physician and sometime mule trader, advocated the use of "metallic tractors" for the treatment
of various diseases of humans and horses.2 The user of the tractors (small metal magnetic wedges) swept the tractors
over the injured area for a few minutes to "draw off the noxious electrical fluid that lay at the foot of suffering." Subjects
and observers perceived immediate benefits. They reported their testimonials and Perkins became very rich. Magnetic tractors
failed to prevent Dr. Perkins' death due to yellow fever in 1799.
In the late 1800s, the Sears catalogue advertised magnetic boot inserts. Magnetic caps
and clothing (with over 700 magnets) were available by mail order from Thatcher's Chicago Magnetic Company. 3 Dr.
Thatcher asserted that "magnetism properly applied will cure every curable disease no matter what the cause."4
At the turn of the 20th century, Dr. Albert Abrams, named the "Dean of 20th Century charlatans" by the American Medical Association,
postulated that each organ system and patient was "tuned" to a characteristic electromagnetic wavelength. By the time of World
War II, physiologic effects of electromagnetic fields no longer received much attention in medical journals.
The history of quackery in the use of magnets has obscured scientific investigations
performed on the medical effects of magnetic and electromagnetic fields. From a biophysics standpoint, a distinction is made
between the two therapies; magnetic and electromagnetic are not the same.
Electricity and Magnetism
Electromagnetism was first discovered in the 1800s by the English physicist Michael
Faraday, who determined that a magnetic field could be generated by running an electric current through a wire coil. Conversely,
a changing magnetic field can generate an electric voltage; the magnetic field must change to have any electrical effect (hence,
the term pulsating electromagnetic field therapy, which generates rising and falling levels of a magnetic field.)
The biological effects of pulsating electromagnetic fields are hypothesized to be due
to electrical rather than magnetic forces. Magnetism generates a voltage in tissue according to the equation:
V = n
x a x dB/dt
V = Voltage
n = number of turns in the electromagnetic coil
a = area of the loop
dB/dt = The rate of change of magnetic field with respect to time, with B representing
the strength of the magnetic field (in Teslas). For example, if B goes from zero to 1 Tesla in 1 millisecond, then dB/dt =
Based on this equation, a static magnetic field cannot generate an electrical voltage,
as the dB/dt component of the equation, is zero, as is the voltage induced by the field. Thus, any effects of a static magnetic
field on tissue cannot be electrical in nature.
Pulsating Electromagnetic Field Therapy
Extracellular matrix synthesis and repair are subject to regulation both by chemical
agents (such as cytokines and growth factors) and physical agents, principally mechanical and electrical stimuli. The precise
nature of such electromechanical signals is not known, however. In bone, mechanical and electrical signals may regulate the
synthesis of extracellular matrix by stimulating signaling pathways at the cell membrane.6,7 In soft tissue, alternating
current electrical fields induce a redistribution of integral cell membrane proteins which, hypothetically, could initiate
signal transduction cascades and cause a reorganization of cytoskeletal structures. 8 However, the hypothesis that
electrical signals may be responsible for information transfer in or to cells has neither been proved nor disproved.
There is ample evidence that electrical activity exists in the body at all times. For
example, electrical currents can be measured in the beating heart and are also generated in the production of bone. Endogenous
electrical current densities produced by mechanical loading of bone under physiologic conditions approximate 1 Hz and 0.1
- 1.0 microA/cm2 .9 Thus, it is theorized that application of an appropriate electrical current, either directly
through wires or indirectly through induction by a magnetic field, may affect tissues in several ways. The word appropriate
in the preceding sentence is important since cells and tissues respond to a variety of electrical signal configurations in
ways that suggest a degree of specificity for both the tissue affected and the signal itself.
The most widely studied application of electromagnetic field therapy in human medicine
is in fracture therapy. Although the mechanisms remain undetermined, several studies report that electrical fields generated
by pulsating electromagnetic field therapy stimulate biologic processes pertinent to osteogenesis10,11,12 and bone
graft incorporation. 13,14 This form of therapy is approved for the treatment of delayed and non-union fractures
in humans in the U.S. by the United States Food and Drug Administration. Effectiveness of the treatment is supported by at
least two double-blind studies.15,16 Pulsating electromagnetic field therapy, however, delays the healing of fresh
experimentally induced fractures in rabbits.17
Pulsating electromagnetic field therapy has also been evaluated in the treatment of
soft tissue injuries, with the results of some studies providing evidence that this form of therapy may be of value in promoting
healing of chronic wounds (such as bedsores)18 , in neuronal regeneration,19,20 and in many other soft
tissue injuries.21,22 results of a recent study in an experimental Achilles tendinitis model in rats indicated
that there was an initial decrease in water content in injured tendons treated with pulsating electromagnetic field therapy
but that all treated groups were equal to controls by 14 days.23The limited value of this form of therapy in the
treatment of tendon injuries may be due in part to the lack of significant electrical activity in tendons, activity that could
be altered by a pulsating electromagnetic field.
In contrast, a number of investigators have been unable to show any effect of low-level
electromagnetic fields on tissue healing. One study, for example, failed to identify any beneficial effect of applying a magnetic
field to a non-healing fracture24 and concluded that the long periods of immobilization and inactivity required
for the application of the magnetic field therapy were just as likely to be responsible for tissue healing.
Criticisms of pulsating electromagnetic field studies include: some of the studies
are poorly designed; independent trials have not been conducted to confirm positive results; and the electrical fields induced
by the machines are several orders of magnitude lower than are required to alter the naturally occurring electrical fields
that exist across biological membranes.25 Even proponents of the therapy concede that much work needs to be done
to optimize such variables as signal configuration and duration of treatment before pulsating electromagnetic field therapy
can be generally recommended.26
Static Magnetic Field Therapy
Magnetic devices that radiate an unchanging magnetic field are available in a variety
of configurations such as pads, bandages, and even magnetic mattresses. Scientific studies do not support claims of efficacy.
Furthermore, a mechanism of action by which such devices might exert these effects remains elusive. Because static magnetic
fields do not change, there can be no electrical effect. Hypotheses for an effect of a static field include influencing the
electronic spin rate states of chemical reaction intermediates27,28 and influencing cyclical changes in the physical
state(s) of water.29 Importantly, neither of these proposed effects has been demonstrated in biological systems
under physiological condition.30
In spite of a lack of demonstrable mechanism of action, proponents of applying static
magnetic field therapy to injured or painful tissues generally attribute their alleged effects to an increase in local blood
circulation. Unfortunately, the scientific evidence in supporting this hypothesis is tenuous at best.
Blood, like all tissues, contains electrically charged ions. A physics principle known
as Faraday's Law states that a magnetic field will exert a force on a moving ionic current. Furthermore, an extension of Faraday's
law called the Hall effect states that when a magnetic field is placed perpendicular to the direction of flow of an electric
current, it will tend to deflect and separate the charged ions. While the deflection of ions will be in opposite directions
depending on the magnetic pole encountered and the charge of the ion, this force is not based on the attraction or repulsion
of like and unlike charges.
The Hall effect implies that when a magnet is placed over flowing blood in which ionic
charges (such as Na+ and Cl-) exist, some force will be exerted on the ions. Furthermore, the separation of ionic charges
will produce an electromotive force, which is a voltage between points in a circuit. In theory, this produces a very small
amount of heat. These physical effects, which do exist, provide the basis for a quasi-scientific theory to account for the
purported effects of static magnetic field therapy. For example:
When a magnetic field with a series of alternating North and South poles is placed over a blood vessel, the
influence of the field will cause positive and negative ions (for example, Na+ and Cl-) to bounce back and forth between the
sides of the vessel, creating flow currents in the moving blood not unlike those in a river. The combination of the electromotive
force, altered ionic pattern, and the currents causes blood vessel dilation with a corresponding increase in blood flow. 31
The problem with using Faraday's law and the Hall effect to explain the purported effects
of static magnetic pads is that the magnitude of that force applied by the field is infinitesimally small. Two facts account
for the lack of effect. First, the magnetic field applied to the tissue is extremely weak. Second, the flow of the ionic current
(i.e., the blood) is extremely slow, especially when compared to the flow of electric current. However, it is possible to
estimate the forces applied to flowing blood by a weak magnetic field as long as the strength of the magnetic field applied,
the velocity of the flowing blood, and the number of the ions in the blood are known.
Magnetic field strength is measured in one of two units: 1 Tesla = 104 Gauss.
The magnetic field strength of a Norfield's MAGNETIChockwrapTM(for horses) measured at California Institute of
Technology had a field strength of 270 Gauss at the level of the pad and 1 Gauss at a distance of 1 cm from the pad. Tissues
purportedly affected by the pads lie at least 1 cm away from them; 1 Gauss is approximately the magnetic field strength of
the earth.32 Promotional information for Bioflex pads asserts an "independent laboratory" has measured the field
strength of their pads at 350 Gauss and that "optimum" field strength for the purported healing effects is less than 500 Gauss.33
Regardless, these are very weak magnetic fields.
Considering the applied magnetic field at 250 Gauss (0.025 Tesla) and the velocity
of blood flow v as 1 cm/sec (0.01 m/sec), the electric field to which an ion in the blood is exposed can be calculated as:
E = v
x B = 2.5 x 10-4 Volts/meter/sec
Hence, the change in electric potential (a psuedo-Hall effect) across a 1 mm diameter
blood vessel can be estimated at a minuscule 2.5 x 10-7 Volts.
Ions of opposing charges will move in opposite directions when moving through a static
magnetic field. The separation of charges, known as the drift velocity, can also be calculated. In the case of Na+ and Cl-
ions in flowing blood under the influence of a 250 Gauss magnetic field, the increased separation of the positive sodium and
the negative chloride ions will be about 0.2 Angstroms per second, or about 1/10 the diameter of an atom. This can be compared
with the random drift distance in one second that results from the thermal agitation imparted by the heat of the horse's body
of about 0.25 mm/sec. Stated in another fashion, the ions will travel farther from thermal agitation than from the 250 Gauss
magneto-electrical field drift by a factor of about 10 million.34
Any magnetic forces generated by a static field affecting fluid movement in blood vessels
would have to overcome both the normal, pressure-driven turbulent flow of blood propelled by the heart and the normal thermal-induced
Brownian movement of the particles suspended in the blood. Given the strong physical forces that already exist in a blood
vessel, any physical forces generated by a static magnetic field on flowing blood, particularly those as weak as those associated
with therapeutic magnetic pads, are extremely unlikely to have a biological effect.
Magnetic Pad Design
At least one manufacturer of magnetic pads (Magnaflex/BioflexTM) asserts
that the effect of charge separation can be increased by alternating north and south magnetic poles. Alternating magnetic
poles are most commonly seen in refrigerator magnets. By alternating the magnetic poles, an increased magnetic gradient is
created, which increases the ability of the magnets to stick to the refrigerator. Paradoxically, alternating poles decrease
the magnetic field strength of the magnet because the fields tend to cancel each other out as they extend from the magnet.
Thus, while alternating poles would exert opposite forces on ions flowing through the magnetic field, the decrease in magnetic
field strength would lessen any potential influence of the magnetic field on the target ions. Nor does there appear to be
any consensus in the industry as to the ideal design for the pads. In fact, a competing manufacturer asserts that, "Leading
scientists agree that unipolar magnets are superior to bi-polar,"35 although neither the scientists nor the supporting
research are identified.
Further proprietary design information regarding at least one commercial source of
magnetic pads (BioflexTM pads) would also appear to be irrelevant regarding biologic effects. Promotional information
for the pads indicates that the "concentric circle" arrangement of the pads increases the likelihood that the magnetic field
would be applied perpendicular to flowing blood, thereby maximizing the Hall effects. In fact, because blood vessels run randomly
throughout the three dimensions of any tissue, there can be no "preferred" arrangement of the magnetic field that would favor
its perpendicular orientation to the flow of blood.
Studies on Static Magnetic Fields and Blood Flow
A number of studies have investigated the effects of static magnetic fields on blood
flow. Studies commissioned by the makers of one type of magnetic pad showed that exposure of a highly concentrated saline
solution in a glass capillary tube increased the flow of the solution. This study has been often cited by manufacturers of
static magnetic devices as evidence that magnetic field therapy can potentially affect the circulation of blood. Although
the mechanism for the increase in saline flow is not apparent, it certainly could not have been related to any dilatory effect
on the walls of the glass capillary tube. The investigator who performed the study concluded that the results of the experiments
performed using highly concentrated saline in a glass tube should not be extrapolated to effects that would be expected with
A second study evaluated the effects of the pads in the distal limbs of horses using
nuclear scintigraphy, a technique that is useful in identifying areas of blood vessel dilation and inflammation. That study
concluded that, "Scintigraphy was performed in the vascular, soft tissue, and bone phase using a cross over trial to demonstrate
increased blood flow and metabolic activity as a result of the local application of a permanent magnetic pad on the equine
metacarpus. A highly significant increase was evident in the three phases."37 The results of this study have been
used repeatedly to suggest that magnetic pads promote blood circulation to the areas under the pads.
This study, which is apparently the only one to state that a static magnetic field
affects blood circulation, is open to criticism. The experimental model, which compared the results of scans on one "treated"
limb vs. the non-treated limb is inherently inaccurate, as one forelimb cannot be used as a control for the other in scintigraphic
studies (each limb should be used as its own control). Furthermore, the design of the study was flawed, as a bandage and magnetic
pad were applied to one limb while a bandage only was applied to the other. A more appropriate control would have been a bandage
and a demagnetized pad. The radioisotope chosen for the study was not appropriate to determine blood circulation accurately.
Finally, the study measured absolute scintigraphic counts, when the use of relative perfusion ratios would have been more
Numerous other studies have failed to show any effect of magnetic fields on blood circulation.
For instance, no effect of dental magnets on the circulation of blood in the cheek could be demonstrated.39 Scintigraphic
evaluation of blood flow in mice exposed to two strengths of pulsating electromagnetic field force failed to demonstrate any
circulatory effects.40 A study on the circulatory effects of a magnetic foil was unable to show any effect in the
skin of human forearms41 and application of a magnetic foil to healing wounds in rats showed no significant effects.42
A study in horses showed that application of a magnetic pad over the tendon region for 24 hours showed no evidence of temperature
increase in treated limbs vs. placebo controlled limbs, using thermographic measurements as an indirect assessment of blood
circulation to the area.43
As a more practical matter, if a magnet caused local increases in circulation, one
would expect the area under the magnet to feel warm or become red as a result. Such an effect is not reported when magnets
are held in the hand. Furthermore, one would expect any circulatory effects produced by very weak magnetic fields to be magnified
in stronger magnetic fields. However, no circulatory effects have ever been reported in magnetic resonance imaging machines,
in which the magnetic forces generated are two to four orders of magnitude greater than those produced by therapeutic magnetic
pads. In studies of humans exposed to magnetic fields up to 1 Tesla (10,000 Gauss) there was no evidence of alterations in
local blood flow at the skin of the thumb or at the forearm.44 Even a 10 Tesla magnetic field is predicted to change
the vascular pressure in a model of human vasculature by less than 0.2%, and experimental results of the effects of strong
magnetic fields on concentrated saline solutions are in general agreement with these predictions.45
Based on the available scientific data, one must conclude that if there is an effect
of static magnetic fields on blood circulation, there is no known biological mechanism by which that effect is generated.
One may also postulate that the boots, blankets, and bandages in which the magnets are sewn have some sort of a thermal effect
that is independent of the magnetic field (and could be duplicated with any form of bandaging).
Magnetic Fields and Pain Relief
Both static and pulsating electromagnetic field therapy have also been promoted as
being beneficial for the relief of pain. As with other proposed effects, there is no known mechanism of action by which application
of a magnetic field produces biological effects. If they are effective in the relief of pain, it is unlikely that the effect
is related to a reduction in nerve conductivity; the field required to produce a 10% reduction in nerve conductivity is roughly
Studies evaluating the effects of pulsating electromagnetic fields in the relief of
pain have shown conflicting results. Pulsating electromagnetic field therapy has reportedly provided pain relief in the treatment
of osteoarthritis of the human knee and cervical spine,47,48 in the treatment of persistent neck pain,49
and in the treatment of women with chronic refractory pelvic pain.50 However, electromagnetic therapy showed no
benefit in the relief of pain due to shoulder arthritis51, and a 1994 summary of published trials of non-medicinal
and noninvasive therapies for hip and knee osteoarthritis concluded that there were insufficient data available to draw any
conclusions on the efficacy of the therapy.52 Paradoxically, another study in humans showed that magnetic treatment
actually induced hyperalgesia in a tooth pain model.53
Pads that apply a static magnetic field are also promoted as having pain-relieving
effects. Poorly controlled studies from the Japanese literature suggest that static magnetic devices were highly effective
in alleviating subjective symptoms such as neck, shoulder, and other muscular pain.54,55 One controlled, double-blind
pilot study suggested that magnetic pads were effective in the relief of myofascial or arthritic-like pain in postpolio syndrome,56
although every patient in the study, whether being treated with a placebo or a magnet, showed relief from pain. However, other
studies have concluded that a magnetic foil offered no advantage over plain insoles in the treatment of pain of the human
heel57 and that a magnetic necklace had no effect on neck and shoulder pain.58 It has also been suggested
that there is a strong placebo effect at work in the perception of pain relief offered by static Magnetic devices.59
Clinical Use of Magnetic Fields in Veterinary Medicine
Magnetic and electromagnetic devices appear not to be used on small animals. However,
the devices are widely advertised in magazines targeted at horse owners. Pulsating electromagnetic field therapy is typically
applied to horses with boots or blankets. Some of the variables of the magnetic field generated (such as the amplitude and
frequency of the signal) can be controlled using this form of magnetic therapy. However, changes in these variables appear
to affect different tissues in different ways, and those ways are not well defined, making selection of ideal field strength
of the therapy problematic.
The other way to apply a magnetic field to a horse is by attaching a magnetic pad.
This form of therapy generates a continuous, static magnetic influence on the targeted tissue; however, the magnetic field
cannot be modulated. The principle advantage of this form of magnetic therapy is that it is relatively inexpensive (compared
to the cost of the machines) and easy to apply; the disadvantage is that as yet there is no scientific evidence of an effect.
The absence of a plausible scientific theory for a mechanism of action should never
override reliable strong clinical evidence of an effect. For example, the mechanism of aspirin was not known for many years,
although the drug was clinically effective. However, there appear to be no published scientific studies available that demonstrate
that any form of magnetic field therapy is valuable in the treatment of disease conditions of the horse.
Daily electromagnetic therapy did increase the concentration of blood vessels in surgically
created defects of equine superficial digital flexor tendon, but the maturation of the repair tissue and the transformation
of collagen type (two essential components in the healing process of tendon) actually were delayed by the treatment in tendon
samples collected at 8 to 12 weeks after surgery.60 No benefit could be demonstrated in the healing of freshly
created bone injuries treated with pulsating electromagnetic field therapy when compared to untreated control limbs, 61
although another study did suggest an increase in bone activity under pulsating electromagnetic field treatment when holes
were drilled in horse cannon bones.62 Topical treatment with a pulsed electromagnetic field showed little effect
on metabolism of normal horse bone in another study.63 Unfortunately, the principle application of pulsating electromagnetic
field therapy in people, for delayed and non-union fractures, is of little apparent use in horses.
Magnetic Therapy and Pseudoscience
In spite of hundreds of years of investigation, there still appears to be no place
for magnetic therapy in scientific medicine. While legitimate investigations are taking place, many aspects of magnetic therapy
carry hallmarks of pseudoscience. For example:
- Vague, unsupported claims of effectiveness.
One device advertises that "leading scientists agree that unipolar magnets are superior to bipolar." The "leading scientists"
are not identified. The company also claims to have "tens of thousands of very satisfied users."
- Misuse of defined scientific terminology. The
discovery of a "unipolar" magnet (see above) or magnetic monopole would lead its discoverer to an almost immediate Nobel prize,
as magnetic monopoles have not been shown to exist. One company advertises its "Tectonic" magnets (tectonics is a geologic
term referring to the study of the earth's structural features.)
- Mischaracterization of medicine. One company
warns about the side effects of taking "too many pills" and states that, "Using magnets means you are not putting anything
into your stomach that might cause upset or damage." Another company describes their magnets as "natural as nature" and "wholistic"
[sic]. While magnets may not have any side effects, they may not have any effects, either.
- Inaccurate claims. One company states that studies
at various universities have "proven" that static magnets increase blood flow. This appears to be contrary to fact.
- Predicted phenomena remain slippery. As experimental
and theoretical work progresses, more and more sound evidence for the related phenomena should appear.64 So far,
such evidence remains elusive in the field of magnetic therapy.
- No deepening evidence. In spite of hundreds
of years of experience and investigation, the "state of the art" in magnetic therapy appears to have increased little since
the days of Franz Mesmer.
Whenever an injury to tissue occurs, the goal of any medical therapy is to help allow
healing of that injury so that, to the extent that it can be done, the injured tissue is returned to full normal function
as quickly as possible. The quality of tissue repair and the speed with which that repair can be accomplished are the two
major variables in the healing of any injury. Any medical therapy that could be demonstrated to affect either variable (or
better yet, both of them) would be extremely valuable to the medical field.
However, assessing whether or not a particular medical therapy is effective in those
regards is somewhat problematic. The old adage, "Time heals all wounds," is largely true. Many diseases are self-limiting
and the body is able to heal itself with no intervention whatsoever. For example, according to one source, approximately 70
per cent of all acute infectious disease conditions of the horse are adequately dealt with by the host's defenses.65
That suggests that whichever method of treatment is selected, 7 out of 10 times, the problem will get better. If healing occurs
while a device touted to promote healing is applied to an injured or infected area, that device often receives the credit.
Explanations that magnetic fields "increase circulation," "reduce inflammation," or
"speed recovery from injuries" are simplistic and are not supported by the weight of experimental evidence. The effects of
magnetic fields on body tissues are complex and appear to vary from tissue to tissue and from different intensities and duration
of the magnetic field applied. The nature of the magnetic devices make them amenable to randomized, controlled, double-blind
studies that are, for the most part, lacking. Although the therapies appear to be harmless, that does not also mean that they
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