Static and low-frequency magnetic field effects: health risks and therapies

Many biological processes are affected by electromagnetic fields. Hence incremental internal fields generated by external magnetic fields can be expected to affect that biology. With some exceptions, most of the present interest in the effects of exogenous static and low-frequency magnetic fields centres on three intensity regions. (1) There are concerns that 50-60 Hz power distribution fields as small as 0.2 µT, may affect the health of populations. (2) ac fields that are larger than 1 mT (and usually smaller than 100 mT) with frequencies of a few kHz or less may have therapeutic value with respect to the healing of bone fractures and soft-tissue injuries. (3) The very large slowly varying fields of the order of 2 T used in magnetic resonance imaging might affect the physiology of the patients. Magnetic fields interact with biological systems through forces on the electrical currents associated with physiological functions and through the torques exerted on the magnetic moments of biologically important molecules and the electrons that play a role in the binding of geminate radicals. The torques that the Earth's magnetic field applies to the ferrimagnetic domains of biologically formed magnetite affects the biology of species in several different phyla and may have consequences in humans. Low-frequency magnetic fields also induce electric fields through the Faraday effect that may have biological consequences. For either the direct magnetic fields or the magnetically induced electric fields to affect the biology of living systems, the interactions with such systems must generally be larger then the interactions with endogenous physiological and thermal noise. This constraint seems to exclude the possibility that the environmental fields less than 1 µT from the electric power distribution system affect health and places important constraints on the minimal fields that can be expected to have therapeutic value.