Long-term residential magnetic field exposure and neurodegenerative disease mortality: An 18-year nationwide cohort study in Switzerland.

The potential health risks associated with exposure to extremely low frequency magnetic fields (ELF-MFs) are still being debated. In 2001, the International Agency for Research on Cancer (IARC) classified ELF-MFs as a possible human carcinogen (Group 2B). The IARC based this classification on "inadequate" evidence from animal studies and "limited" epidemiological evidence linking exposure above 0.3 to 0.4 μT to childhood leukemia. In addition to cancer, exposure to ELF-MFs is suspected to increase the risk of neurodegenerative diseases. One previous study [1] observed an increased mortality rate from Alzheimer’s disease among individuals who had lived near high-voltage power lines for a long time in Switzerland. Subsequent studies in Denmark and Italy provided weak evidence of an increased rate of Alzheimer’s disease and negative results for other neurodegenerative diseases. Electrical appliances and indoor wiring are the most common sources of indoor ELF-MF exposure for the general population. However, such exposure is typically intermittent and of short duration. In contrast, proximity to outdoor sources, such as high-voltage power lines and railway infrastructure, is a better indicator of long-term exposure.

The analysis is based on data from approximately 3.5 million adults from the Swiss National Cohort (2001–2018). Using the SNC database, the researchers created a closed cohort with an 18-year follow-up period, including only individuals who were 30 years of age or older at the start of the study (2001). Long-term ELF-MF exposure from high-voltage power lines (50 Hz) and railway lines (16.7 Hz) was modeled using validated proximity models. The horizontal distance to the nearest high-voltage power line or railway line was calculated and entered into the models as an input parameter. The proximity models were validated using a subset of measurements taken in 59 private households. Strong correlations were observed between the predicted and measured exposure for single- and multi-track railway lines. However, measured ELF-MF exposure decreased with increasing distance from high-voltage power lines only for the lines with the highest voltages (220–380 kV). In contrast, distance from 36 to 150 kV high-voltage power lines did not correlate with measured ELF-MF exposure, likely because other sources (e.g. household appliances) dominated the measured exposure levels. For this reason, these were excluded from the analysis. Long-term ELF-EMF exposure levels were calculated as a time-weighted average over 10-year time windows. Hazard ratios (HRs) were estimated for mortality due to Alzheimer’s disease (AD), other types of dementia (OTD), amyotrophic lateral sclerosis (ALS), Parkinson’s disease (PD), and multiple sclerosis (MS), also considering sociodemographic and environmental co-exposures. Air pollution and noise levels were also included.

Less than 1% of the population was exposed to long-term ELF-MF levels of ≥ 0.3 µT from high-voltage power lines, while 2.4% were exposed from railway lines. No associations were observed for ALS, PD, or MS. After adjusting for sociodemographic and environmental co-exposure, an increase of 1 µT in exposure to high-voltage power lines was associated with a 54% higher risk of AD-related mortality (95% CI 1.23–1.92). For other types of dementia, the associations were weaker. Each 1 µT increase in exposure was associated with a 31% higher risk of mortality (95% CI 1.13–1.52). The associations between ELF-MFs from railway lines and mortality from AD and other types of dementia were less consistent than those observed for high-voltage power lines. Exposure to railway lines was positively associated with AD mortality in minimally adjusted models (HR = 1.15; 95% CI 1.06–1.24) and in models adjusted for sociodemographic factors. However, the association weakened after adjusting for environmental co-exposures (HR = 1.08, 95% CI 0.99–1.18). A similar pattern was observed for the other types of dementia.

The results presented here regarding the risk of dying from Alzheimer’s disease are consistent with an earlier analysis of the Swiss National Cohort [1]. These findings also align with the repeatedly observed increased risk of dementia among individuals exposed to strong ELF-MF fields. However, the underlying biological mechanisms remain unclear. Several neurodegenerative mechanisms have been proposed to explain this association, including alterations in neuronal ion channels, epigenetic dysregulation, and oxidative stress. Assuming the observed associations are causal and considering that exposure to high levels of ELF-MFs from high-voltage power lines or railway lines is uncommon, the population-attributable fractions of Alzheimer’s cases would be 1.01% and 0.43%, respectively. (AT)

1. Huss A, Spoerri A, Egger M, Röösli M, Swiss (2009). Residence near power lines and mortality from neurodegenerative diseases: Longitudinal study of the Swiss population. American Journal of Epidemiology, 169(2), 167–175. https://doi.org/10.1093/aje/kwn297