Occupational exposure to extremely low frequency magnetic fields or electric shocks and cancer incidence in four Nordic countries

Objectives To evaluate the association between occupational exposure to extremely low frequency magnetic fields (ELF-MF) or electric shocks and brain cancer, haemopoietic and lymphatic malignancies, and breast cancer incidence in the Nordic Occupational Cancer cohort. Method The cohort was set up by linking occupational information from national censuses held in 1960, 1970, 1980-1, and/or 1990 to national cancer registry data in Finland, Iceland, Norway, and Sweden. All subjects aged 30-64 years who participated in a census were followed-up for cancer incidence until 2003-2005. Occupational exposure to ELF-MF or electric shocks (low, medium, high) was assigned to each subject based on census reported jobs using job-exposure matrices. For each case, five controls were randomly selected by matching for country, age, and sex. Conditional logistic regression models were performed adjusting for social class and occupational exposure to solvents. Results A total of 68 770 brain cancer cases, 65 609 non-hodgkin lymphoma cases, 83 088 leukaemia cases, 33 791 multiple myeloma cases, 1827 male breast cancer cases, and 297,283 female breast cancer cases were included. Thirty-five percent of the total population was ever exposed to medium levels of ELF-MF and 7% to high levels, whereas 19% was ever exposed to a medium risk of electric shocks and 13% to a high risk. No associations were found between occupational exposure to ELF-MF or electric shocks and any of the cancer outcomes. Conclusions In this very large census cohort we found no evidence of increased risk of several cancers in relation with occupational exposure to ELF-MF or electric shocks.