Epidemiological study (observational study)

Occupational exposure to extremely low frequency magnetic fields and mortality from cardiovascular disease epidem.

By: Hakansson N, Gustavsson P, Sastre A, Floderus B

Published in: Am J Epidemiol 2003; 158 (6): 534-542

Aim of study (acc. to author)

The relation between occupational exposure to extremely low frequency (ELF) magnetic fields and mortality from cardiovascular diseases was investigated in the population of Swedish twins.

Further details

Exposure was assessed by linking occupation reported in 1967 or 1973 to a job exposure matrix. Four levels of exposure to extremely low frequency magnetic fields were related to cause-specific mortality through 1996. A further aim of the study was to elavuate whether genetic susceptibility to cardiovascular disease modifies the relation between exposure and disease.

Endpoint/type of risk estimation

cardiovascular diseases: acute myocardial infarction, ischemic heart disease, arrhythmia

Type of risk estimation:

mortality

(relative risk (RR))

Exposure

- occupational

Assessment

questionnaire: in 1967 or 1973
job exposure matrix: geometric mean of average workday mean values

Exposure groups

Group	Description
Reference group 1	low magnetic field exposure: < 0.10 µT
Group 2	medium magnetic field exposure: 0.10 - 0.19 µT
Group 3	high magnetic field exposure: 0.20 - 0.29 µT
Group 4	very high magnetic field exposure: ≥ 0.30 µT
Reference group 5	no genetic susceptibility & magnetic field exposure < 0.20 µT
Group 6	no genetic susceptibility & magnetic field exposure ≥ 0.20 µT
Group 7	genetic susceptibility & magnetic field exposure < 0.20 µT
Group 8	genetic susceptibility & magnetic field exposure ≥ 0.20 µT

Population

Group:
- men
- women
Age: 15–81 years
Characteristics: same-sex twins with death diagnosis cardiovascular disease
Observation period: 1967/1973 - 1996
Study location: Sweden
Data source: Swedish Twin Registry, causes-of-death registry
Exclusion criteria: students, housewives, other subjects without an occupation, and subjects with jobs not included in job exposure matrix

Study size

Type	Value
Total	27,790

Other:

person-years of follow-up: 613,133

Statistical analysis method:

Cox proportional regressions analysis

(adjustment:

age
sex
smoking, body mass index

)

Results (acc. to author)

There was no overall increase in mortality from cardiovascular disease across the exposure groups. In the absence of genetic susceptibility to the disease, a small effect was seen for magnetic fields below 0.20 µT, and a strong effect was found for genetic susceptibility in the absence of extremely low frequency magnetic fields. The joint prevalence of the two factors showed the strongest increase in risk (RR 2.68, CI 1.09, 6,58), and a synergistic effect was indicated, particularly among monozygotic twins.

Limitations (acc. to author)

Exposure was assessed by questionnaire without taking duration of exposure into account. Exposure assessment is based on the job exposure matrix without individual measurements. The analyses of genetic susceptibility and exposure was based on low numbers.

Study funded by

Swedish Council for Working Life and Social Research (FAS)

Koeman T et al. (2013): Occupational exposure to extremely low-frequency magnetic fields and cardiovascular disease mortality in a prospective cohort study
McNamee DA et al. (2011): The response of the human circulatory system to an acute 200-muT, 60-Hz magnetic field exposure
McNamee DA et al. (2010): The cardiovascular response to an acute 1800-microT, 60-Hz magnetic field exposure in humans
Cooper AR et al. (2009): A population-based cohort study of occupational exposure to magnetic fields and cardiovascular disease mortality
Lednev VV et al. (2008): Modulation of cardiac rhythm in the humans exposed to extremely weak alternating magnetic fields
Ahlbom A et al. (2004): Occupational Magnetic Field Exposure and Myocardial Infarction Incidence
Sahl J et al. (2002): Occupational magnetic field exposure and cardiovascular mortality in a cohort of electric utility workers
Savitz DA et al. (1999): Magnetic field exposure and cardiovascular disease mortality among electric utility workers