Workplace exposure to very low frequency electromagnetic fields may be linked to a doubling in risk of developing the most common form of motor neurone disease, amyotrophic lateral sclerosis, or ALS for short, suggests research published online in Occupational & Environmental Medicine.
Previous research has suggested that ALS might be linked to workplace exposure to extremely low frequency electromagnetic fields, electric shocks, solvents, metals, and pesticides, but flaws in the design of these studies undermined their findings.
This latest study relied on data from the Netherlands Cohort Study, which has been looking at diet and cancer. It involves more than 58,000 men and more than 62,000 women aged between 55 and 69, and began in 1986.
Participants who had died of motor neurone disease (76 men and 60 women) were compared with around 4,000 (2,411 men and 2,589 women) who had been randomly selected for the purposes of the current study.
Their detailed employment histories were converted into workplace exposure to solvents, pesticides, metals, extremely low frequency magnetic fields and electric shocks, using a validated technique (job exposure matrices).
High levels of electromagnetic field exposure were largely confined to the men, and depended on job type. Participants’ neurological health was then tracked for an average of 17 years.
Occupational exposure to extremely low frequency electromagnetic fields was associated with a heightened risk of developing ALS among the men. Those whose jobs had exposed them to high levels of extremely low electromagnetic fields were more than twice as likely to develop ALS as those who had never been exposed through their work. Furthermore, those in the top 30% of cumulative exposure (duration x intensity) were nearly twice as likely to develop the disease.
The other occupational factors assessed were only weakly associated with ALS risk in both men and women.
While this is an observational study so no firm conclusions can be drawn about cause and effect, the researchers said that their findings strengthen the evidence suggesting that ALS may be linked to workplace exposure to extremely low electromagnetic fields.
Prof Roel Vermeulen, co-author of the paper, said: “ELF-MF are magnetic fields produced by electrical appliances and the power grid, with a frequency up to 300 Hz. Jobs with relatively higher ELF-MF levels are for example: electric line installer, repairers and cable jointer, welders, sewing-machine operators, air craft pilots. Essentially jobs where workers are placed in close proximity to appliances that use a lot of electricity.”
Prof Malcolm Sperrin, Director of Medical Physics and Clinical Engineering at the Royal Berkshire NHS Foundation Trust, highlighted that such fields are “different from the fields associated with WiFi, domestic power transmission etc. where to date there is no conclusive evidence of an elevated health risk.”
Prof Paul Pharoah, Professor of Cancer Epidemiology at the University of Cambridge, said: “Even though the study was very carefully conducted there are two main problems with the results. The first is that chance is the most likely explanation for the findings. The researchers evaluated ten different exposures in men and in women. If none of these exposures were associated with a risk of ALS then by chance an apparent association (statistically significant) would be observed in 1 out of 20 exposures. “
He added: “A second problem is that, even if the association between extremely low frequency magnetic fields and ALS were not due to chance, association does not mean causation. It is likely that occupational exposure to extremely low frequency magnetic fields is correlated with many other factors that could be the cause of the observed association.”
