History

Magnet therapy in the treatment of various medical conditions dates back as early as 200 AD with Greek healers reportedly using magnetic rings as a treatment for arthritis.¹ During the Middle Ages, magnets were thought to be effective in the treatment of baldness, wounds, arthritis, and gout.¹ In the early 1600s, an English physician, Thomas Browne, may have been one of the first to scientifically evaluate magnets. He concluded that the use of magnets in the treatment of such diseases as gout, headache, and venereal disease amounted to wishful thinking.¹ Because of its continued popularity as an alternative therapeutic modality and the business that it generates, therapeutic efficacy has been studied in various models.

Magnets continue to be in use today, with a myriad of products available claiming various therapeutic values. An Internet search² of magnetic therapy for dogs yields products such as beds, collars, and jackets, among others, that claim to have beneficial effects on pain, blood flow, tissue oxygenation, bone and tissue regeneration, inflammation, and sleep. The current literature is sparse, however, and little convincing evidence exists for these claims. For all of these applications, increased blood flow is one theory provided to explain why magnets may have an effect. At this time no solid explanation for why magnets may have a physiologic effect seems to be available. Unfortunately, only weak evidence exists, not only for the effects of pain alleviation and bone or wound healing, but also for the theorized cause, blood flow changes. When studies have shown a potential physiologic effect, the mechanism causing the effect is often poorly explained or may be more strongly associated with a placebo effect.

Effects on Blood Flow

The Lorentz force law states that a magnetic field exerts a force on a moving ionic current.³ The Hall effect further 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.³ Ions will be deflected in opposite directions depending on the magnetic pole encountered and the charge of the ion.³ In theory, when a magnetic field with a series of alternating north and south poles is placed over a blood vessel, the influence of the field may cause positive and negative ions to bounce back and forth between the sides of the vessel, creating currents in moving blood similar to those in a river.³ The combination of the electromotive force, altered ionic pattern, and currents may potentially cause blood vessel dilation with a corresponding increase in blood flow.⁴ However, magnetic forces are smaller than the physical forces already present caused by the heart muscle.³

The iron in hemoglobin causes blood to be only weakly repelled or attracted by magnets.⁵ If they were attracted to a magnet this could have a clotting effect negatively affecting circulation.³ Static magnets, to be effective, must overcome the strong physical forces of blood flow propelled by the heart and normal thermal induced Brownian random movement of the particles suspended in the blood, which is unlikely.³

Increased flow rates of concentrated saline have been observed within a glass capillary tube under the influence of a magnetic field.³ The reason for the increased flow is not explained but because the capillary cannot expand, it cannot be related to vasodilation.³ However, the investigator of this study warns that these findings should not be extrapolated to tissue perfusion.⁶ Many studies have shown static magnets to be ineffective in altering circulation both in animal and human studies regardless of the level of magnetic field.³

In a study performed on six horses, the effect of static magnetic therapy on blood flow was assessed in the metacarpal region.⁷ Red blood cells were labeled with Tc 99m phosphate and dorsal images of both metacarpi were acquired with a gamma camera. One metacarpus was treated with a magnetic wrap with 270 G at its surface, and the other metacarpus was treated with an identical wrap in which the magnets had been replaced with identical size and weighted polytetrafluoroethylene sheet. The metacarpi were treated for 48 hours and the scintigraphy was repeated. No significant difference was noted in perfusion of the metacarpal region between groups. The authors noted that in the commercially available wraps used in this study, the strength of the magnetic field dropped off to 0.5 G at 7 mm from the surface of the magnet, making it unlikely that the underlying blood vessels were actually exposed to a clinically relevant magnetic field. Static magnetic fields have also been shown to have no significant effect on mucosal blood flow in humans,⁸ soft tissue healing in rats,⁹ or blood flow to the skin of rats.¹⁰

Pain Alleviation

A variety of theories exist attempting to explain how magnets may provide pain relief. Likewise, a wide variety of protocols with varying magnetic strengths is observed in the literature. One theory to explain pain relief is associated with increased or altered blood flow. As discussed previously, little to no evidence supports the contention that magnets have a measureable effect on blood flow. A second theory to explain pain relief is reduced nerve conductivity. This theory proposes that nociceptive C fibers have a lower threshold potential and that magnetic fields selectively attenuate neuronal depolarization by shifting the membrane resting potential.¹¹ However, this is an unlikely theory as a 10% reduction in nerve conductivity would require 24 T,¹² a field strength obtained only in the strongest superconducting magnets used for research.³

Clinical Effects

Perhaps one of the most successful studies conducted on the use of static magnets to treat pain was done by Vallbona and colleagues¹³ on 50 patients with postpolio syndrome who reported muscular or arthritic pain. Based on a hypothesis that magnets applied over trigger points would have the greatest effect, they applied static magnets ranging in strength from 300-500 G to palpated trigger points for 45 minutes while patients remained in the experimental setting.¹³ This study was double-blinded and appears to be one of the best-controlled studies using magnets because patients had little opportunity to test for magnetism. Pain levels were assessed by palpation of trigger points before and after application of the magnetic device. The McGill pain questionnaire was used to evaluate subjective pain, elicited by palpation of the single most painful trigger point, even if multiple sites were present. Following application of the magnets, trigger points were again palpated and pain was reassessed by the subjects. Twenty-two patients in the active group showed improvement as compared with four in the placebo group, a significant difference.

In 2007, Pittler and colleagues¹⁴ published a systematic review and metaanalysis of 29 randomized trials in humans on the effect of static magnets on pain and concluded that the evidence does not support the use of magnets for pain relief for low back pain, delayed-onset muscle soreness, or foot pain.¹⁴ The exceptions to this finding were three double-blinded randomized controlled trials assessing pain relief in osteoarthritis (OA) that found pain reductions relative to placebo when treatments lasted 2 to 12 weeks.¹⁴ A separate study evaluated the use of magnets continuously for 24 hours and found that there was no pain relief. The authors concluded that for the condition of OA, there is insufficient evidence to exclude a clinically beneficial effect and believed that further investigation might be warranted.¹⁴

In a large randomized double-blind study assessing the effectiveness of magnet therapy on pain intensity and opioid requirements in human patients with acute postoperative pain, investigators found no difference in pain intensity level or opioid requirement between groups treated with magnets or sham magnets.¹⁵ Patients with various abdominal surgeries or lipoma excision were treated with quadrapolar static magnets of 1900 G strength placed at the ends of the incisions and around them and left in place for 2 hours. The control group was treated with sham magnets of equal weight and size. Patients rated their pain via a numerical rating scale and the number of rescue doses of morphine was recorded. The authors concluded that magnetic therapy should not be used for treatment of postoperative acute pain or any pain that results from tissue injury.¹⁵

A comparison of commercially available static bipolar magnetic shoe insoles with identical sham insoles in 101 human subjects diagnosed with plantar fasciitis (heel pain) showed no significant difference in outcome variables studied.¹⁶ Insoles were worn for at least 4 hours a day, 4 days a week for 8 weeks. The sham group reported significant improvement in morning foot pain intensity, and both groups reported an improvement in how much foot pain interfered with their employment enjoyment; however, magnets did not induce additional benefit over nonmagnetized insoles. The sham insoles used in this study averaged a surface reading of 2.2 G and active magnetic insoles averaged 192.1 G.¹⁶

In a multicenter, double-blinded, placebo-controlled study investigating the role of static magnetic insoles on diabetic peripheral neuropathy–caused neuropathic foot pain, investigators found that chronic use of 450 G multipolar, static magnetic shoe insoles significantly reduced symptoms of burning, numbness, tingling, and exercise-induced foot pain compared with sham insoles.¹⁷ Subjects wore magnetic insoles or sham insoles for 24 hours per day for 4 months and tabulated validated daily pain scores and unvalidated quality of life scores. No new analgesic drugs were allowed during the study. Significant differences between groups were not apparent until after the second month of treatment. Of note was that the magnitude of the reduction of burning, numbness, tingling, and exercise-induced foot pain, especially in the severe and extreme cases, was comparable or better than those previously reported for gabapentin, tramadol, and lamotrigine studies.¹⁷ The mechanism of action of the magnets is unknown, but this study suggests that long-term use may be required to see improvement in symptoms.

The effectiveness of commercially available magnetic bracelets for pain control in OA of the hip and knee in people was evaluated in a multicenter, randomized, placebo-controlled trial.¹⁸ Three groups were evaluated over a 12-week period: (1) standard strength static bipolar magnetic bracelet, (2) a weak magnetic bracelet, or (3) a nonmagnetic (dummy) bracelet. Mean pain scores using the standardized validated Western Ontario and McMasters Universities score were reduced more in the standard magnet group than in the dummy group (27% change from baseline). However, some patients discovered that the bracelets had a magnetic field, resulting in unblinding, although the analysis indicated that this had a small effect on the results. The authors concluded that pain from OA of the hip and knee decreases when wearing magnetic bracelets, but it remains uncertain whether the effect is due to specific or nonspecific (placebo) effects.

Studies on magnets for therapeutic purposes in animals are limited. Two studies by workers from Hungary demonstrated a reduction of writhing from visceral pain in mice induced by intraperitoneal injection of acetic acid. Mice were treated by placing them in a cage with magnets with nonhomogeneous 2-754 mT strength. The pain reaction was significantly reduced in the treated mice compared with mice injected and placed in cages without the magnetic field.19,20 The authors hypothesized that the observed effect was somehow mediated by the peripheral opioid system because naloxone antagonized the static magnetic field–induced analgesic response if given peripherally but not centrally.²⁰

One study determined the effect of a permanent magnetic field on the progression of OA in a canine model.²¹ OA was created by transecting a cranial cruciate ligament. Dogs were subjected to no floor mattress, a floor mattress with ceramic pieces placed between two layers of foam but no magnetic field (sham control), or a floor mattress with ceramic permanent magnets placed between two layers of foam. The magnetic field had a surface field strength of 1100 G, whereas the magnetic field strength at the surface of the mattress was 450-500 G and was equally distributed over the surface. The magnetic mattress group appeared to have less synovitis, less synovial effusion, less disruption of the cartilage surface, and less cartilage ulceration than did the other groups. Histologic scores for OA were less in the magnetic mattress group as compared with the other groups, but the differences were not statistically significant. There were similar trends in immunohistochemical studies for matrix metalloproteinase (MMP)-1 and MMP-3, with the magnetic mattress group having less staining; this group had similar MMP-3 to normal cartilage. The mattress and magnetic field group did not differ from the normal group in MMP-3 as determined by Western blot analysis. The results of this study suggest that cartilage exposed to a magnetic field may have reduced progression of OA early in the disease process. Further studies are needed to confirm this and to delineate the mechanisms of action that magnetic fields may have in reducing the progression of OA.