Magnetic fields have been linked to childhood cancer in many countries and now it's also been shown in Japan. Michinori Kabuto, of the National Institute of Environmental Studies in Ibaraki, along with a number of collaborators have found that children exposed to 4 mG (0.4 µT) or more in their bedrooms had close to five times more leukemia than those living in low-exposure homes. This statistically significant finding appears in the August 1st issue of the International Journal of Cancer.
One big advantage of this study is that it's the first to measure residential magnetic fields over the course of a full week, rather than just 24 hours —as was the case, for instance, in the 1997 U.S. National Cancer Institute study. These extra measurements show that there was a great deal of variation in homes with high-field levels. Kabuto explains that when he compared the leukemia risk for each of the seven days separately, the leukemia risk on the highest exposure day was nearly twice that for the lowest exposure day. That's a big difference and could explain some of the inconsistencies in past studies.
On the negative side, the participation rate for the controls was less than 30%, which is extremely low. Kabuto was well aware that this could have played havoc with his entire study and he did what he could to investigate its implications. "[S]election bias per se cannot fully explain our positive finding," he concludes.
Whatever its strength and weaknesses, the Japanese study is the last major epidemiological study of EMFs and childhood leukemia we can expect for a long time. Decisions concerning the adoption of precautionary policies will have to be made with the information we now have in hand.