[Magnetic fields and health: from epidemiology to cryptochrome chemistry]

Biological effects of static magnetic fields (MF) and time-varying MF of electricity (50/60 Hz) appear possible from intensities in the low illitesla range. However, prolonged exposure to 50/60 Hz MF is associated with an increased risk of childhood leukemia at less than one microtesla of time-averaged intensity. And such kind of association is suggested in adults for some blood cancers and senile dementia. The cryptochrome hypothesis has been proposed to explain the association established with childhood leukemia. Cryptochromes indeed assume the regulation of circadian biorhythms (a disruption of these lasts takes part to carcinogenesis) and they could be intrinsically sensitive to MF as from the low microtesla range. The cryptochrome hypothesis is now supported by diverse experimental observations. And recently, its relevance is further enhanced by the perspective of possible photo-dependence of the clock function of Cry 2 in retina, at least in diurnal mammals - the magnetic sensitivity of cryptochromes is indeed photo-dependent. Such a perspective however implies some major paradigm shifts in the experimental study of biological effects of 50/60 Hz MF as it has been conducted to date. On the other hand, the cryptochrome hypothesis can in principle also apply to static MF. For these, indeed, a mechanism of interaction with cryptochromes is identified, which is not the case of 50/60 Hz MF so far. A hypothesis is proposed here for these last, namely, resonance-based interaction with the spin polarization of one or both the radicals of the long-lived (milliseconds) pair FAD°-Trp4°.