Magnetic Fields and the Body

The electrochemical processes of the human body are extremely complex and incompletely understood, and physical effects of magnetic fields cannot be ruled out. Many thousands of papers have in fact been published on biological effects of electromagnetic fields, much of it focused on the effects of radio-frequency and microwave fields or, in recent years, on fields at power-line frequencies (fifty or sixty cycles per second). Studies of biological effects of steady magnetic fields (reviewed by Frankel and Liburdy 1996) have concentrated mostly on high fields of the level encountered in MRI magnets, typically of the order of 10,000 gauss (1 tesla). Unfortunately, research has been very limited at field levels typical of magnetic therapy products, most of which are limited to a few hundred gauss, even at the magnet surface. (The earth's field is a bit less than half a gauss.)

Viewed simply as inert material, the human body, like its primary constituent, water, is diamagnetic, i.e., weakly repelled by magnetic fields. In response to an applied magnetic field, the electrons in water molecules make slight adjustments in their motions, producing a net magnetic field in the opposing direction about 100,000 times smaller than the applied field. With the removal of the applied field, the electrons return to their original orbits, and the water molecules once again become nonmagnetic. (We perhaps should note that some promoters of magnetic therapy also promote "magnetized water." You can't magnetize water. Although water responds weakly to an applied field, the response disappears as soon as the field is removed.) Although the diamagnetism of water and most living things is very weak, a high-field electromagnet producing 160,000 gauss (16 tesla) at the center of the coil has recently been used to levitate not only water drops but also flowers, grasshoppers, and small frogs (Berry and Geim 1997), the "flying frogs" drawing worldwide media coverage. Since fields of that magnitude are required to balance gravitational forces, the much lower fields of magnetic-therapy devices can only produce diamagnetic forces that are thousands of times smaller than gravity. (The repulsive force will be proportional to the product of the field and the field gradient.)

Some dubious literature suggests that magnetic fields attract blood, citing all the iron it contains. However, iron in the blood is very different from metallic iron, which is strongly magnetic because the individual atomic magnets are strongly coupled together by the phenomenon we call ferromagnetism. The remarkable properties of ferromagnetic materials are a result of the cooperative behavior of many, many magnetic atoms acting in unison. The iron in blood consists instead of isolated iron atoms within large hemoglobin molecules, located inside the red blood cells. Although each of the iron atoms is magnetic, it is not near other iron atoms, and remains magnetically independent.

The net effect of the weak paramagnetism of the isolated iron atoms in hemoglobin is only a slight decrease in the overall diamagnetism of blood. Blood, like water, is weakly repelled by magnetic fields, not attracted.

Although most components of the human body and other living things are weakly diamagnetic, many organisms have been shown to contain small amounts of strongly magnetic materials, usually magnetite (Fe3O4). The most extreme case is that of magnetotactic bacteria, originally found in mud collected from the marshes of Cape Cod. Each contains a long chain of magnetite particles that interact strongly enough with the earth's magnetic field to orient the bacteria along the field. Magnetite crystals have also been found in pigeons, honeybees, many mammals, and even in the human brain, but in proportionately much smaller amounts than in the bacteria. It seems very unlikely that there is enough magnetite within the human body to provide a possible mechanism to explain magnetic therapy. However, if magnetite particles were located at strategic places, they could locally amplify the effects of low magnetic fields and, for example, modify ion flow across cell membranes, of the type involved with electrical transmission in nerve cells.

More likely mechanisms are those based on magnetic forces on moving charged particles, possibly including ions or charged molecules in flowing blood, moving across cell membranes, moving across synapses between nerve cells, etc., or those based on more subtle effects on biochemical reactions (Frankel and Liburdy 1996). Although no physical mechanisms for magnetic therapy have been established, the possibilities are numerous and complex. Only further clinical tests, carefully controlled to account for placebo effects, can confirm or dispute the results of the Baylor study and prove or disprove the claims of magnetic therapy.

Some media reports have not sufficiently distinguished the Baylor form of magnetic therapy, based on modest static fields from permanent magnets, with a more accepted form of "magnetic therapy" based on high pulsed magnetic fields from electromagnets (Malmivuo and Plonsey 1995). Pulsed magnetic fields are very different from static magnetic fields, because, via Maxwell's equations, time-varying magnetic fields induce electric fields. Electric fields have pronounced biological effects, particularly on nerve and muscle cells, as we have known since the days of Galvani and his twitching frogs' legs. Many years ago the FDA approved the use of pulsed magnetic fields in "bone growth stimulators" for the treatment of fractures that were slow to heal, and research on "magnetic stimulation" -- pulsed magnetic fields applied to the brain or other components of the nervous system -- has grown rapidly in recent years. Transcranial magnetic stimulation, in which the patient receives hundreds of magnetic field pulses of 1 tesla or more, each only a millisecond in duration, has shown considerable promise as a means of treating depression. However, these forms of pulsed-field magnetic therapy are based on biological effects of induced electric fields, and are very different from the use of the static fields from permanent magnets.