Occupational exposure to extremely low frequency magnetic fields and the risk of chronic diseases

Abstract

Interest in the health effects of ELF-MF among adults has focused on cardiovascular diseases, breast and brain cancer, leukaemia, and neurodegenerative diseases. Of these, brain cancer, leukaemia, amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease have shown the strongest associations with increased ELF-MF exposure, although this evidence is inconsistent. We investigated the association between occupational exposure to extremely low frequency magnetic fields (ELF-MF) and cardiovascular and neurodegenerative disease mortality and cancer incidence. We aimed to improve on earlier studies by investigating this association within the prospective, general population Netherlands Cohort Study (NLCS), using state-of-the-art job-exposure matrices (JEM) and a full occupational history to assess exposure, and controlling for potential confounding by behavioural and other occupational exposures. The NLCS was started in 1986 and contains 120,852 men and women aged 55 to 70 years. Employing a case-cohort approach, the person-years for the entire cohort are estimated using a subcohort of 5,000 subjects. Occupational history and information on potential confounders is available for the period up to baseline. Occupational exposure to ELF-MF was assigned to jobs on the basis of a recently developed ELF-MF JEM. The association between ELF-MF and health endpoints was estimated using Cox proportional hazards regression. The combined results of our analyses showed positive associations for acute myeloid leukaemia, follicular lymphoma, ALS and Parkinson’s disease. Other health endpoints showed no associations. The negative findings for ELF-MF and cardiovascular diseases and breast cancer are in line with the current epidemiological evidence. The literature on brain cancer and leukaemia incidence is inconsistent, although current findings on brain cancer seem to go into the direction of no association. Our results add to the findings of no association for brain cancer and a positive association for leukaemia. Follicular lymphoma has not been reported in association with ELF-MF before. Non-Hodgkin lymphoma as an overarching group has generally shown no effects in the literature. This stresses the importance of looking into subtypes of non-Hodgkin lymphoma for health effects. Studies on ALS and Alzheimer’s disease are inconsistent, but seem to point into the direction of a possible association between ELF-MF and these diseases. Our analyses support an association for ALS, but not for dementia including Alzheimer’s disease. Lastly, the epidemiological evidence on the association of Parkinson’s disease with ELF-MF is generally negative, and our finding of a possible positive association is therefore unexpected. Our study had a number of strengths: i) use of an extensive occupational history , ii) improved ELF-MF-JEM to assign exposure and iii) having the ability to correct for potential confounding from behavioural variables and other occupational exposures. The use of mortality instead of incidence to identify cases of cardiovascular and neurodegenerative diseases was a significant drawback of this study. An overview of the literature shows that the effects of ELF-MF exposure on subtypes of hemato-lymphoproliferative malignancies, ALS and Alzheimer’s disease still warrant further study. These studies should focus on improving the exposure assessment and using incident cases for these health outcomes .