There have been many studies linking magnetic fields to illness, especially children growing up under power lines. I've been recently acquainted with a researcher who used a Gaussmeter to measure the field strength near a school which had an unusually high incidence of leukemia among it's students. Power lines 30 feet away from the school were thought to play a role, but they found out that badly installed wiring a portable was creating intermittant fields which they believe to be the cause.
We don't know exactly why or how it happens, but there is evidence that EMFs do cause negative health effects.
http://www.dhs.ca.gov/ps/deodc/ehib/emf/RiskEvaluation/riskeval.html
Read chapter 21, conclusions, if you want to get to the point.
