Epidemiological study (observational study)

Case-control study on occupational exposure to extremely low-frequency electromagnetic fields and glioma risk epidem.

By: Carlberg M, Koppel T, Ahonen M, Hardell L

Published in: Am J Ind Med 2017; 60 (5): 494-503

Aim of study (acc. to author)

The association between occupational exposure to extremely low-frequency magnetic fields and glioma risk was investigated in a case-control study in Sweden.

Endpoint/type of risk estimation

brain tumor: glioma

Type of risk estimation:

incidence

(odds ratio (OR))

Exposure

- 50/60 Hz
- magnetic field
- occupational

Assessment

questionnaire: occupational history including job title, branch, first and last year for each job
job exposure matrix
calculation: cumulative exposure, average exposure, maximum exposed job

Exposure groups

Group	Description
Reference group 1	cumulative exposure: < 2.33 µT-years
Group 2	cumulative exposure: 2.33 - < 3.79 µT-years
Group 3	cumulative exposure: 3.79 - < 5.55 µT-years
Group 4	cumulative exposure: 5.55 - < 8.52 µT-years
Group 5	cumulative exposure: ≥ 8.52 µT-years
Reference group 6	average exposure: < 0.11 μT
Group 7	average exposure: 0.11 - < 0.13 μT
Group 8	average exposure: 0.13 - < 0.18 μT
Group 9	average exposure: 0.18 - < 0.27 μT
Group 10	average exposure: ≥ 0.27 μT
Reference group 11	maximum exposed job: < 0.13 μT
Group 12	maximum exposed job: 0.13 - < 0.16 μT
Group 13	maximum exposed job: 0.16 - < 0.24 μT
Group 14	maximum exposed job: 0.24 - < 0.60 μT
Group 15	maximum exposed job: ≥ 0.60 μT

Population

Group:
- men
- women
Age: 19–80 years
Observation period: 1997 - 2003, 2007 - 2009
Study location: Sweden

Case group

Characteristics: brain tumor, histopathologically verified
Data source: Swedish cancer registry

Control group

Selection:
- population-based
Matching:
- sex
- 5-year age group

Study size

	Cases	Controls
Participants	1,346	3,485
Participation rate	86 %	86 %

Statistical analysis method:

unconditional logistic regression
restricted cubic splines analysis, interaction analysis between occupational ELF-MF exposure and mobile phone and cordless phone use

(adjustment:

age
sex
socioeconomic status
year of diagnosis

)

Results (acc. to author)

Overall, no significant increased risk for glioma was observed in the groups with occupational exposure to extremely low frequency magnetic fields (groups 2-5, 7-10, 12-15) in comparison with the respective reference groups. However, a significant increased risk for the glioma subtype astrocytoma grade IV (glioblastoma multiforme) was observed with cumulative exposure in the time window 1-14 years before diagnosis (highest cumulative exposure category (≥ 2.75 µT): OR 1.9, CI 1.4-2.6), but not in the time window of 15 years and longer (highest cumulative exposure category (≥ 6.59 µT): OR 0.9, CI 0.6-1.3).
No statistically significant interaction between occupational exposure to extremely low frequency magnetic fields and mobile phone and cordless phone use was found.
The authors conclude that an increased risk in late stage (promotion/progression) of astrocytoma grade IV for occupational exposure to extremely low frequency magnetic fields was found.

Study funded by

Cancer och Allergifonden (Cancer and Allergy Foundation), Sweden
Cancerhjälpen (Cancerhelp), Sweden
Kone Foundation, Finland
Mr Brian Stein
Pandora Foundation, Germany

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