A recently published paper exploring the connection between occupational risk factors and MND has sparked lots of interest, especially by the media. The study in question, led by Dr Roel Vermeulen from Utrecht University, The Netherlands, reviewed and studied five occupational exposures that had previously been suggested to be associated with developing MND (specifically, amyotrophic lateral sclerosis; ALS). These factors included exposure to electromagnetic fields, electrical shocks, solvents, metals and pesticides. While a few studies investigating these factors were already conducted in the past, their results are not consistent.
Despite the vast coverage of this topic in tabloids, we wanted to describe the research paper itself – to explain what exactly the researchers did, what they found and what it all means.
How was the study conducted?
In their study, the researchers used a database of over 120,000 people that were a part of The Netherlands Cohort Study on diet and cancer. This register was set up in 1986 and only included people who were 55-69 years of age. Out of the whole register, 158 people (88 men and 70 women) died of ALS – these were the cases whose data were used for the analyses.
As part of the enrolment to the database, the participants were asked detailed questions on a variety of topics, including lifestyle, dietary habits and previous occupations. Specific for this study, the researchers focused on the type and nature of companies the participants had worked for, their job title and time period of employment. They then looked at occupational exposure using a job-exposure matrix, which looks at the harmful factors for specific occupations (eg electricians are more likely to be exposed to electric shocks than other occupations). Further calculations relating to the time period of each employment and the number of paid jobs before joining the database gave an ‘exposure score’ (eg working as an electrician for 1 month will likely result in less electric shocks than in electricians who were in the profession for 30 years). This then yielded three levels of exposure (background – ie no exposure at work, low and high) for each of the five potentially harmful factors.
What was found?
The main finding revealed that men who were exposed to high levels of extremely low frequency magnetic fields (ELF-MF) at work were twice as likely to develop ALS compared to those with lower exposure levels. It is important to note that due to the low number of women working in high ELF-MF jobs, the analysis was only done on men. To get an idea of where someone might be exposed to ELF-MFs, any profession that involves working closely with high-voltage electricity appliances is a likely candidate. A study by van Tongeren et al (2009) showed that people working as welders, or office and records assistants in electricity industry are exposed to these magnetic fields more than those in other occupations.
For all other occupational risk factors, that is, electric shocks, metals, solvents and pesticides, the researchers did not find any strong association with ALS.
So what does this mean?
This study tells us that high and repetitive exposure to ELF MFs, specifically at work, might be one of the many environmental factors that contribute to developing ALS, alongside genetic and lifestyle influences. We have to bear in mind that, with a sample of 88 men, out of which only 9 were classed as having high occupational exposure to ELF MF, the results should be treated with caution. Most importantly, this study only showed a trend (ie higher likelihood of having ALS with higher exposure to ELF-MF) and did not confirm causation (ie we cannot say that exposure to ELF-MF causes ALS).
However, there are lots of follow-up questions that researchers can address in the future that stem from this study. For example, the precise effect of ELF-MF on ALS can now be investigated in more detail. The impact of other environmental factors that have been associated with MND can also be researched more thoroughly by utilising similar study design.
Our Director of the Research Development team, Dr Brian Dickie, sums it up: “The results suggest that exposure to high levels of extremely low frequency magnetic fields is associated with an increased risk of developing MND. However, this only becomes apparent when relatively large numbers of people are studied, indicating that any such effect is a very subtle one. It does not mean that exposure causes MND.”
Original research paper: Koeman T, Slottje P, Schouten LJ, et al. Occupational exposure and amyotrophic lateral sclerosis in a prospective cohort. Occupational and Environmental Medicine, March 2017.