Occupational magnetic field exposure and myocardial infarction incidence

Background: Studies on healthy volunteers have seen reduced heart rate variability after exposure to extremely low-frequency electric and magnetic fields (EMF). Because reduced heart rate variability has been linked to cardiovascular disease risk, it has been hypothesized that exposure to EMF might increase the risk of cardiovascular disease. One epidemiologic study has shown increased mortality from cardiovascular conditions in utility workers with elevated exposure to magnetic fields, but several other epidemiologic studies have failed to confirm this result. We tested the hypothesis that occupational EMF exposure increases the risk of myocardial infarction in a large population-based case-control study of myocardial infarction, with detailed information on potential confounders. Methods: We used data from the SHEEP study, which is a population-based case-control study of acute myocardial infarction in Stockholm. Occupational EMF exposure was based on job titles 1, 5, and 10 years before diagnosis. We used 2 approaches to classify exposure: first, specific individual job titles with presumed elevated EMF exposure, and second, classification of subjects according to a job-exposure matrix. Results: We found no increased risk of myocardial infarction in subjects classified as having elevated EMF exposure. For the highest exposure category of greater than or equal to0.3 muT according to the job-exposure matrix, the adjusted relative risk was = 0.57 (95% confidence interval 0.36-0.89). Conclusions: The results of this study do not support the hypothesis that occupational EMF exposure increases the risk of myocardial infarction.