Occupational exposure to electromagnetic fields and chronic diseases

Abstract: This thesis consider two exposures from the electromagnetic spectrum extremely low-frequency magnetic fields (ELF MF) and ultraviolet (UV) radiation. ELF MF are the lowest and UV radiation ranges among the highest frequencies of non-ionizing radiation. The exposure prevalence of these fields is high in the general population. Most people are exposed daily to either or both types and potential health effects are of great concern. The aim of the thesis was to study occupational exposure to ELF MF and UV radiation in relation to cancer, neurodegenerative diseases and cardiovascular diseases. A cohort with an increased prevalence of individuals highly exposed to ELF MF was created in order to be able to study exposure-response relations. In all, four cohort studies and one case-control study were performed. Exposure-response relationships were found for occupational ELF MF exposure and certain cancer diseases: malignant brain tumors among women, tumors of the pituitary gland among men. Welders were at an increased risk of tumors of the endocrine glands. The outcome might indicate an interaction with the hormonal system. A potential effect of occupational ELF MF exposure in cancer development cannot be rejected. In the study of neurodegenerative diseases, the risk of both amyotrophic lateral sclerosis and Alzheimer s disease increased with increasing exposure to ELF MF. The results confirm previous findings of an association, and further epidemiological studies are needed, preferably based on morbidity data and taking into account potential confounding from e.g. electric shocks. For acute myocardial infarction (AMI), a low level increase in relative risk was found as well as an exposure-response relation. Joint occurrence of ELF MF exposure and a genetic susceptibility for AMI showed a synergistic effect on AMI mortality. Effect modification from e.g. genetic predisposition to the disease deserves to be further explored in studies of ELF MF and AMI. Swedish construction workers exposed to sunlight from outdoor work were at an increased risk of myeloid leukemia, lymphocytic leukemia or non-Hodgkin s lymphoma and stomach cancer. These findings are possibly due to an effect of UV radiation on the immune system. Sunlight exposure was also associated with an increased risk of malignant melanoma of the eye. Extensive research has been carried out in relation to ELF MF. There is yet no evidence of any biological mechanisms that could explain how ELF MF might contribute to cause chronic diseases. Therefore, additional efforts to explore potential pathways are warranted. Also, the question of effect modification from individual sensitivity such as genetic predisposition and interactions with other environmental factors deserves to be further explored.