This article is from the Static Electromagnetic Fields and Cancer FAQ, by John Moulder firstname.lastname@example.org and the Medical College of Wisconsin with numerous contributions by others.
There are known biological mechanisms through which strong (greater than
2000 mT) static magnetic fields could cause biological effects [1,50],
but these mechanisms could not account for biological effects of static
fields with intensities of less than about 200 mT [1,50]. It is
conceivable that biological effects could be mediated through effects on
free radical reaction rates at field strengths as low as 0.1 mT
[56,57,71]; but there is no evidence that such effects have any
biological significance .