Residential and occupational exposure to 50-Hz magnetic fields and brain tumours in Norway: a population-based study

Our case-control study was conducted to investigate whether residential and occupational exposure to magnetic fields increased the risk for brain tumours in adults. Data from an occupational exposure matrix was also evaluated. The study population in this nested case-control study was made up of subjects aged 16 years and older who had resided in a broad corridor around a high-voltage power line in 1980 or during one of the years from 1986-1996. The cases were incident cases diagnosed during 1980-96. Two controls were matched to each case by year of birth, sex, municipality and first year entering the cohort. The time-weighted average exposure to residential magnetic fields generated by the power lines was calculated for the exposure follow-up from 1 January 1967 to diagnosis. In addition, job titles and branches of industry were classified as categories of hours per week in a magnetic field above background level (0.1 microT). Exposures were cumulated over occupationally active years for the exposure follow-up from 1 January 1955 to diagnosis. When residential magnetic fields are evaluated, the 2 upper residential, time-weighted, average magnetic field categories showed elevated odds ratios (ORs) for all brain tumours (OR = 1.6; 95% confidence interval [95%CI] 0.9-2.7 and OR = 1.3; 95% CI 0.7-2.3). Occupational exposure showed no association to exposure for any site. We found an elevated risk for residential exposure to magnetic fields and brain tumours, although the risk was not significant, and no clear exposure-response pattern was found. The findings for the occupational exposure groups showed an inverse association.