Do low-frequency magnetic fields cause diseases of the nervous system?

Neurodegenerative diseases imply a progressive loss of cells in the nervous system. These diseases, which are usually slow-advancing and often lead to motor and cognitive impairment, include Parkinson’s, Alzheimer’s, multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS).

Whether there is a connection between electromagnetic fields and neurodegenerative diseases has been the subject of scientific research for many years. With this in mind, the Federal Office for Radiation Protection (BfS) stays abreast of the latest studies and follows up on new evidence through its own research.

Current status: epidemiological observational studies indicate a connection between Alzheimer’s and ALS and low-frequency magnetic fields

Previous epidemiological studies provided evidence that some neurodegenerative diseases may occur more frequently in the event of occupational exposure to low-frequency magnetic fields. This applies to ALS and Alzheimer’s disease. A meta-analysis of 42 cohort and case-control studies from 2013 indicates a link between occupational exposure to low-frequency magnetic fields and neurodegenerative diseases^[1]. This evidence was partially confirmed in a meta-analysis from 2019, which found an approximately 10% increase in the risk of developing ALS or Alzheimer’s^[2]. There was, however, no increase in the risk of developing Parkinson’s disease or multiple sclerosis.

What is amyotrophic lateral sclerosis (ALS)?

ALS is the most common motor neurone disease in adults and usually progresses rapidly. Motor neurones are nerve cells that control the muscles and whose death leads to progressive paralysis. As with Alzheimer’s, scientists only have a rudimental understanding of the causes and molecular basis for the disease’s development and its progression.

The familial form of the disease involves mutations in several genes that play a role in, above all, protein formation, the maintenance of protein balance and oxidative defence, such as the gene for the enzyme superoxide dismutase (SOD1), which is involved in oxidative processes.

Does occupational exposure to magnetic fields or living near a high-voltage power line increase the risk of developing ALS?

An increased risk of developing ALS was found in workers who were occupationally exposed to low-frequency magnetic fields. This was the result of an evaluation of 20 epidemiological studies as part of a meta-analysis in 2018^[3]. There are indications that, as well as with the average magnetic field exposure, the risk of ALS also increases due to electric shocks, which can occur more frequently in occupationally exposed persons^{[4, 5, 6, 7]}. A pooled case-control study from 2019 concluded that magnetic fields and electric shocks may increase the risk of ALS independently of one another^[8]. The most recent systematic review, which dates from 2021, also showed a weak but consistent link between occupational exposure to low-frequency magnetic fields and the occurrence of ALS. However, this meta-analysis, which included 27 studies, showed no link between electric shocks and the occurrence of ALS^[9]. In contrast, a British cohort study from 2022, which included almost 38,000 occupationally exposed individuals, found no increased risk of developing ALS^[10].

A 2018 meta-analysis of five original studies found no link between ALS and living near high-voltage power lines^[11]. This was confirmed in a meta-analysis of four original studies in 2022^[12].

What is Alzheimer’s disease?

Alzheimer’s is the most common form of dementia. It is a progressive neurodegenerative disease in which cognitive abilities decline over a period of decades. Both the causes and the molecular basis of the disease are still only partially understood.

The most conspicuous pathological changes in Alzheimer’s disease are protein deposits (amyloid plaques) in the brain. These are mainly composed of the amyloid-ß peptide and hyperphosphorylated tau protein. Mutations in the gene of the amyloid-ß precursor protein (APP) are responsible for a proportion of familial Alzheimer’s cases and lead to increased production of Aß fragments, which accumulate to form plaques. In addition to the pathological signs mentioned above, there is also an increased activation of glial cells (supporting cells in the nervous system) as well as an impairment of protein balance.

Does occupational exposure to magnetic fields or living near a high-voltage power line lead to an increased risk of developing Alzheimer’s?

A 2018 meta-analysis of 20 epidemiological studies revealed an increased risk of developing Alzheimer’s in the event of occupational exposure to magnetic fields^[13]. In a more recent study in 2020, various work-related circumstances were examined in connection with the occurrence of dementia (type and complexity of work as well as passivity and activity at work). The results of the meta-analysis also indicated a possible link between occupational exposure to low-frequency magnetic fields and the occurrence of dementia^[14].

A 2009 Swiss study of the general population (i.e. not of occupationally exposed persons) provided indications of a possible increased risk of dying from Alzheimer’s in people living less than 50 metres from a high-voltage power line (220–380 kilovolts). This risk increased with the duration of residence^[15]. A 2013 study with a similar methodological structure was unable to fully confirm these findings^[16]. A population-based case-control study from Italy published in 2019 showed a very weak, non-significant increase in the probability of a higher incidence of Alzheimer’s and Parkinson’s in people living up to 50 metres from power lines compared to those living more than 600 metres away^[17].

A narrative review from 2020 identified contradictory studies of the association between low-frequency magnetic fields and Alzheimer’s, with the results of the included studies ranging from disease-reducing to non-existent to intensifying effects. The review included low-frequency magnetic fields as well as high-frequency electromagnetic fields and ionising radiation with regard to their effect on Alzheimer’s disease^[18].

Do experimental laboratory studies support the epidemiological observations?

From 2008 to 2013, the BfS funded the research project „Effects of low-frequency magnetic fields on the development and progression of neurodegenerative diseases in an experimental model“ (only in German). This project investigated whether evidence from epidemiological studies could be confirmed in controlled laboratory experiments on mice. The principal finding of the molecular biological, biochemical and histological analyses, as well as the behavioural studies, was that low-frequency magnetic fields had no negative influence on the course of ALS and Alzheimer’s in the corresponding mouse model ^[19]. This was in keeping with the results of a French study published during the project period, in 2009, that found that a magnetic field had no influence on ALS in the mouse model^[20]. A study from China, published in 2015, also found that low-frequency magnetic fields had no influence on learning ability or protein deposits in the brains of rats^[21].

The report on the study’s results (only in German) was published in the Digital Online Repository and Information System (DORIS) of the BfS.

Conclusion: contradictory literature on ALS and Alzheimer’s

In summary, the results of the individual studies of ALS and Alzheimer’s are inconsistent. Overall, the majority of studies pointed to the same finding for occupational groups that are exposed to significantly higher levels of magnetic fields than the general population: there appears to be a weak but consistent link between exposure to low-frequency magnetic fields and the risk of developing ALS and Alzheimer’s, and this correlation is more pronounced for ALS on the whole than for Alzheimer’s. No link was found between Parkinson’s or multiple sclerosis and magnetic fields^{[12, 22, 23]}. However, the results of the epidemiological studies were not supported by the results of experimental studies on animals.

It remains unclear whether the observed correlations between low-frequency magnetic fields and neurodegenerative diseases are actually cause-and-effect relationships. Likewise, the underlying mechanisms are also unclear. Inflammation, oxidative stress and the immune system play important roles in ALS and Alzheimer’s, and current research is pursuing the hypothesis that these processes might be promoted by magnetic fields. There is no scientific proof of such an effect^[24].

Outlook: research continues as part of the “Radiation protection in electricity grid expansion” programme

A possible increased risk of neurodegenerative diseases due to exposure to magnetic fields is taking on renewed importance in the context of power grid expansion in Germany, and further research is needed to clarify a possible causal relationship. Accordingly, research into neurodegenerative diseases is a key focus of the BfS research programme “Radiation protection during power grid expansion”. To this end, the international workshop “Relationship between neurodegenerative diseases and magnetic field exposure – state of knowledge and research perspectives” was held in Munich in 2017 with a view to recording the current state of knowledge, identifying any gaps in knowledge and highlighting new potential avenues for research. The report on the workshop’s results was published in the Digital Online Repository and Information System (DORIS) of the BfS.

Literature

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