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

Greenland S, Sheppard AR, Kaune WT, Poole C, Kelsh MA

Epidemiology, October 2000, Volume 11, Number 6 2000

Childhood Leukemia-EMF Study Group*

Abstract. We obtained original individual data from 15 studies of magnetic fields or wire codes and childhood leukemia, and estimated magnetic-field exposure for subjects with sufficient data to do so. Summary estimates from 12 studies that supplied magnetic-field measures exhibited little or no association of magnetic fields with leukemia when comparing 0.1-0.2 and 0.2-0.3 microtesla (mT) categories to the 0-0.1 m T category, but the Mantel-Haenszel summary odds ratio comparing >0.3 m T to 0-0.1 mT was 1.7 (95% confidence limits (CL) = 1.2-2.3). Similar results were obtained using covariate adjustment and spline regression.

The study-specific relations appeared consistent despite the numerous methodologic differences among the studies. The association of wire codes with leukemia varied considerably across studies, with odds-ratio estimates for very-high current versus low-current configurations ranging from 0.7 to 3.0 (homogeneity P = 0.005).

Based on a survey of household magnetic fields, an estimate of the U.S. population attributable fraction of childhood leukemia associated with residential exposure is 3% (95% CL = -2%, 8%).

Our results contradict the idea that the magnetic-field association with leukemia is less consistent than the wire-code association with leukemia, although analysis of the 4 studies with both measures indicates that the wire-code association is not explained by measured fields. The results also suggest that appreciable magnetic-field effects, if any, may be concentrated among relatively high and uncommon exposures, and that studies of highly exposed populations would be needed to clarify the relation of magnetic fields to childhood leukemia.