Epidemiological study (observational study)

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

By: Klaeboe L, Blaasaas KG, Haldorsen T, Tynes T

Published in: Int J Cancer 2005; 115 (1): 137-141

Aim of study (acc. to author)

A population-based case-control study was conducted in Norway to investigate whether residential and occupational exposure to 50-Hz magnetic fields increased the risk for brain tumour.

Further details

The study population included all adults in Norway living in a corridor around a high-voltage power line (33 to 420 kV, 40 to 300 m). Residential exposure was calculated as time-weighted average of the magnetic fields generated by power lines. Occupational exposure was assessed as follows: the jobs were classified in categories of hours per week in a magnetic field above background level (0.1 µT), the categories were cumulated and multiplied by number of years working in the job.

Endpoint/type of risk estimation

brain tumor

Type of risk estimation:

incidence

(odds ratio (OR))

Exposure

- 50/60 Hz
- magnetic field
- power transmission line
- occupational
- residential

Assessment

job exposure matrix: based on occupational data of censuses 1960, 1970, 1980, and 1990
calculation: time-weighted average magnetic field of residence close to high-voltage power line based on height of towers, distance between phases, ordering of phases, distance between power line and house, average load on the power line

Exposure groups

Group	Description
Reference group 1	not exposed
Group 2	residential magnetic fields: < 0.05 µT
Group 3	residential magnetic fields: 0.05 - 0.19 µT
Group 4	residential magnetic fields: ≥ 0.20 µT
Group 5	occupational magnetic fields: < 18 (occupational exposure category - years)
Group 6	occupational magnetic fields: 18 - 30 (occupational exposure category - years)
Group 7	occupational magnetic fields: ≥ 31 (occupational exposure category - years)

Population

Group:
- men
- women
Age: ≥ 16 years
Observation period: 1980 - 1996
Study location: Norway

Case group

Characteristics: brain tumor
Data source: Cancer Registry of Norway

Control group

Selection:
- population-based
Matching:
- sex
- age
- area
- case:control = 1:2

Study size

	Cases	Controls
Eligible	454	908

Statistical analysis method:

conditional logistic regression

(adjustment:

5-year age group
sex

)

Results (acc. to author)

90 % of the cases and 92 % of the controls had a residential exposure to magnetic fields of less than 0.05 µT( background level).
A statistically non-significant, moderately elevated risk for residential exposure to magnetic fields and brain tumors was observed. However, no clear exposure-response pattern was found. Occupational exposure to magnetic fields showed an inversed association to the risk of brain tumor.

Study funded by

Research Council of Norway

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