A pooled analysis of magnetic fields, wire codes, and childhood leukemia

We obtained original individual data from 15 studies of magnetic fields or wire codes and childhood leukemia, and we estimated magnetic field exposure for subjects with sufficient data to do so. Summary estimates from 12 stud ies that supplied magnetic field measures exhibited little or no associatio n of magnetic fields with leukemia when comparing 0.1-0.2 and 0.2-03 microt esla (muT) categories with the 0-0.1 muT category, but the Mantel-Haenszel summary odds ratio comparing >0.3 muT to 0-0.1 muT was 1.7 (95% confidence limits = 1.2, 2.3). Similar results were obtained using covariate adjustmen t and spline regression. The study-specific relations appeared consistent d espite the numerous methodologic differences among the studies. The associa tion of wire codes with leukemia varied considerably across studies, with o dds ratio estimates for very high current us low current configurations ran ging from 0.7 to 3.0 (homogeneity P = 0.005). Based on a survey of househol d magnetic fields, an estimate of the U.S. population attributable fraction of childhood leukemia associated with residential exposure is 3% (95% conf idence limits = -2%, 8%). Our results contradict the idea that the magnetic field association with leukemia is less consistent than the wire code asso ciation with leukemia, although analysis of the four studies with both meas ures indicates that the wire code association is not explained by measured fields. The results also suggest that appreciable magnetic field effects, i f any, may be concentrated among relatively high and uncommon exposures, an d that studies of highly exposed populations would be. needed to clarify th e relation of magnetic fields to childhood leukemia.