A pooled analysis of extremely low-frequency magnetic fields and childhood brain tumors

Abstract

Pooled analyses may provide etiologic insight about associations between exposure and disease. In contrast to childhood leukemia, no pooled analyses of childhood brain tumors and exposure to extremely low-frequency magnetic fields (ELF-MFs) have been conducted. The authors carried out a pooled analysis based on primary data (1960-2001) from 10 studies of ELF-MF exposure and childhood brain tumors to assess whether the combined results, adjusted for potential confounding, indicated an association. The odds ratios for childhood brain tumors in ELF-MF exposure categories of 0.1-<0.2 μT, 0.2-<0.4 μT, and ≥0.4 μT were 0.95 (95% confidence interval: 0.65, 1.41), 0.70 (95% CI: 0.40, 1.22), and 1.14 (95% CI: 0.61, 2.13), respectively, in comparison with exposure of <0.1 μT. Other analyses employing alternate cutpoints, further adjustment for confounders, exclusion of particular studies, stratification by type of measurement or type of residence, and a nonparametric estimate of the exposure-response relation did not reveal consistent evidence of increased childhood brain tumor risk associated with ELF-MF exposure. These results provide little evidence for an association between ELF-MF exposure and childhood brain tumors.

Figure 1.

Odds ratios (solid line) and 95% confidence intervals (dashed lines) for childhood brain tumors in a moving window of extremely low-frequency magnetic field exposure levels, adjusted for age at diagnosis, gender, and study, 1960–2001. Reference category: <0.1 μT.

Figure 2.

Nonparametric estimates of trend in the log odds of childhood brain tumors according to extremely low-frequency magnetic field exposure, with a range of smoothing levels from a generalized additive model using a natural cubic smoothing spline for exposure, 1960–2001. Results were adjusted for age at diagnosis, gender, and study. Rug plots at the bottom of each panel indicate the exposure values of subjects included in the analysis. Panel A, 2 df; panel B, 3 df; panel C, 4 df; panel D, 5 df. Dashed lines, 95% confidence interval.

Figure 3.

Influence analysis of the summary odds ratio for childhood brain tumors according to extremely low-frequency magnetic field exposure of ≥0.4 μT versus <0.1 μT, with omission of individual studies, 1960–2001. Results were adjusted for age at diagnosis, gender, and study. Bars, 95% confidence interval.