EPRI Comments on a Study of Occupational Magnetic Field Exposure and Alzheimer’s Disease
Davanipour Z, et al.  “A case-control study of occupational magnetic field exposure and Alzheimer’s disease: results from the California Alzheimer’s Disease Diagnosis and Treatment Centers.”  BMC Neurology, 9 June 2007, 7:13.  This case-control study examines the possible association between occupational magnetic field exposure and Alzheimer’s disease (AD) among patients residing in eight California Alzheimer’s Disease Diagnosis and Treatment Centers located throughout the state.  Cases were 1502 patients, over the age of 65 at first examination, who were diagnosed with probable or definite AD.  Controls were 396 similar patients whose dementia was not related to AD or vascular causes.  Subjects were assigned to magnetic field exposure categories based on their reported primary occupations by one investigator using his expert judgment.  Thirty-two (2.1%) cases and 3 (0.8%) controls had high exposure (average individual exposure > 1 µT or regular intermittent exposures > 10 µT), while 81 (5.4%) cases and 12 (3.0%) controls had medium exposure (average individual exposure 0.2–1.0 µT or regular intermittent exposures > 1 µT).  High-exposure occupations included garment workers, pilots, and welders.  Logistic regression analyses showed significant risk factors for AD, including magnetic field exposure, gender, stroke, and age.  Combining results from this study with those of two previous studies by the same authors yielded an odds ratio of 3.7 (p < 0.001) for sewing machine operators.  The authors conclude that, “Elevated occupational MF [magnetic field] exposure was associated with an increased risk of AD . . . Sewing machine operators . . . are likely to be at increased risk of developing AD, for some reason.  It is important to confirm this statement with targeted studies and, if confirmed, to determine the etiologically relevant exposure(s).”
 
EPRI suggests caution in interpreting the authors’ conclusions.  Since no information was available on the length of employment in primary occupations and occupational histories may have been obtained by interviews with proxies, significant exposure misclassification may have occurred.  Increased risk for AD observed among sewing machine operators could be linked to other exposures in their work environment and not necessarily to magnetic field exposure.  Small numbers of controls in the high- and medium-exposure categories (3 and 12, respectively) make risk estimates quite unstable.  Finally, the authors’ overall conclusion appears to be more in favor of an association than conclusions reached in recent publications, including an Environmental Health Criteria monograph on extremely low frequency (ELF) electric and magnetic fields (EMF) by the World Health Organization (WHO) and a consensus report from an Edinburgh, Scotland workshop on occupational ELF EMF epidemiology, soon to be a submitted manuscript.  According to the workshop report, “although studies of EMF and AD have been fraught with methodological difficulties and have yielded inconsistent results, there is some suggestion for an association.”  Both the workshop report and the WHO monograph call for further research.  These comments (1015351) are available to Program 60 members on epri.com.  For more information, contact Gabor Mezei, (650) 855-8908, gmezei@epri.com.