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.
|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|
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.
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.