Occupational exposure to extremely low frequency electric and magnetic fields and Alzheimer disease: a meta-analysis.

BACKGROUND Among potential environmental risk factors for Alzheimer disease (AD), occupational exposures have received some attention, including extremely low frequency electromagnetic fields (ELF-EMF). A systematic review and meta-analysis of published epidemiological studies on this subject was carried out. METHODS The search was concluded in April 2006. Bibliographic databases consulted included PubMed, EMBASE, Cochrane Library and NIOSHTIC2. Pooled estimates were obtained using random-effects meta-analysis. Sources of heterogeneity between studies were explored, as was publication bias. RESULTS Fourteen different studies (nine case-control and five cohort studies) accomplished inclusion criteria. All these studies followed standardized criteria for AD diagnosis and most of them obtained quantitative estimates of exposure. Pooled estimates suggest an increased risk of AD from case-control studies (OR(pooled) 2.03; 95% CI 1.38-3.00) and from cohort studies (RR(pooled) 1.62; 95% CI 1.16-2.27), with moderate to high statistical heterogeneity in both cases (respectively, I(2) = 58% and I(2) = 54%). Cohort studies showed consistently increased risks for exposed men (RR(pooled) 2.05; 95% CI 1.51-2.80, I(2) = 0%). Evidence of dose-response relationship was not present. Test for publication bias suggests small study effects, mostly for case-control studies. CONCLUSIONS Available epidemiological evidence suggests an association between occupational exposure to ELF-EMF and AD. However, some limitations affecting the results from this meta-analysis should be considered. More information on relevant duration and time windows of exposure, on biological mechanisms for this potential association and on interactions between electromagnetic fields exposure and established risk factors for AD is needed.