Neurodegenerative disorders

The main neurodegenerative disorders are Alzheimer's disease, Parkinson's disease, and Amyotrophic Lateral Sclerosis (ALS, known in the USA as Lou Gehrig's disease).  For Alzheimer's disease, see also a compilation of the abstracts of the epidemiological studies dealing with this and information on a new study in 2008 by Huss et al further down this page.

Conclusions of review bodies on neurodegenrative disorders generally

View of NRPB

In November 2001 the NRPB’s Advisory Group published a Report on electromagnetic fields and neurodegenerative disease. The conclusion was:

There is no good ground for thinking that exposure to extremely low frequency electromagnetic fields can cause Parkinson’s disease and only very weak evidence to suggest it could cause Alzheimer’s disease. The evidence that people employed in electrical occupations have an increased risk of developing amyotrophic lateral sclerosis is substantially stronger, but this could be because they run an increased risk of having an electric shock rather than any effect of long-term exposure to the fields per se. More on NRPB

In its new advice on exposure guidelines in 2004, the NRPB stated:

Studies of occupational exposure to ELF EMFs do not provide strong evidence of associations with neurodegenerative diseases. The only possible exception concerns people employed in electrical occupations who appear to have an increased risk of developing amyotrophic lateral sclerosis; however, this may be due to effects of electric shocks rather than any effect of long-term exposure to the fields per se. More on NRPB

View of ICNIRP

A major review published by ICNIRP in 2002 concluded:

For reasons discussed in the preceding sections, the ALS [amyotrophic Lateral sclerosis] results are intriguing and point toward a possible risk increase in subjects with EMF exposure. However, confirmatory studies are needed, as is an appropriate consideration of confounding, for example, from electric shocks, as a conceivable explanation. As for AD [Alzheimer’s disease], it appears the excess risk is constrained to studies with weaker designs; thus support for the hypothesis of a link between EMF and AD is weak. More on ICNIRP

View of SCENIHR

SCENIHR is the European Commission's Scientific Committee on Emerging and Newly Identified Health Risks. In their opinion on EMFs in 2007 they stated:

For several of the other outcomes the support was never strong. Nevertheless, several neurodegenerative diseases are still considered worthy of study in this respect, and this refers particularly to ALS (amyotrophic lateral sclerosis) and Alzheimer disease.

In a 2009 update they said:

New epidemiological studies indicate a possible increase in Alzheimer's disease arising from exposure to ELF. Further epidemiological and laboratory investigations of this observation are needed.

In their latest 2015 update they say in the main text:

Only few new studies have been published since the previous Opinion. Although the new studies in some cases have methodological weaknesses, they do not provide support for the previous conclusion that ELF MF exposure increases the risk for Alzheimer's disease.
 Then in the summary they say:
Epidemiological studies do not provide convincing evidence of an increased risk of neurodegenerative diseases, including dementia, related to power frequency MF exposure.

More on SCENIHR

View of WHO

The WHO Environmental Helath Criteria Monograph published in 2007 concluded:

It has been hypothesized that exposure to ELF fields is associated with several neurodegenerative diseases. For Parkinson's disease and multiple sclerosis the number of studies has been small and there is no evidence for an association with these diseases. For Alzheimer's disease and amyotrophic lateral sclerosis (ALS) more studies have been published. Some of these reports suggest that people employed in electrical occupations might have an increased risk of ALS. So far, no biological mechanism has been established which can explain this association, although it could have arisen because of confounders related to electrical occupations, such as electric shocks. Overall, the evidence for the association between ELF exposure and ALS is considered to be inadequate.


The few studies investigating the association between ELF exposure and Alzheimer's disease are inconsistent. However, the higher quality studies that focused on Alzheimer morbidity rather than mortality do not indicate an association. Altogether, the evidence for an association between ELF exposure and Alzheimer's disease is inadequate.

 More on the WHO Monograph

The Huss et al study from Switzerland

We give here more information on one important study that was published in the American Journal of Epidemiology in 2008, of neurodegenerative disorders in Switzerland in relation to proximity to power lines. See the press release by the university concerned.

It reports an association between living within 50 m of a power line (particularly for longer periods) and Alzheimer's disease but not ALS, Parkinson's disease or multiple sclerosis.

Results for Alzheimer's disease

The relative risks for subjects living at various distances from the power lines are shown here (for the subjects who had lived there at least 15 years):

graph of Huss results by distance

And the relative risks for various durations of residence are shown here, for subjects living within 50 m:

graph of Huss results by duration of exposure

Abstract

Am J Epidemiol. 2008 Nov 5. [Epub ahead of print]
Residence Near Power Lines and Mortality From Neurodegenerative Diseases: Longitudinal Study of the Swiss Population.
Huss A, Spoerri A, Egger M, Röösli M; for the Swiss National Cohort Study.The relation between residential magnetic field exposure from power lines and mortality from neurodegenerative conditions was analyzed among 4.7 million persons of the Swiss National Cohort (linking mortality and census data), covering the period 2000-2005. Cox proportional hazard models were used to analyze the relation of living in the proximity of 220-380 kV power lines and the risk of death from neurodegenerative diseases, with adjustment for a range of potential confounders. Overall, the adjusted hazard ratio for Alzheimer's disease in persons living within 50 m of a 220-380 kV power line was 1.24 (95% confidence interval (CI): 0.80, 1.92) compared with persons who lived at a distance of 600 m or more. There was a dose-response relation with respect to years of residence in the immediate vicinity of power lines and Alzheimer's disease: Persons living at least 5 years within 50 m had an adjusted hazard ratio of 1.51 (95% CI: 0.91, 2.51), increasing to 1.78 (95% CI: 1.07, 2.96) with at least 10 years and to 2.00 (95% CI: 1.21, 3.33) with at least 15 years. The pattern was similar for senile dementia. There was little evidence for an increased risk of amyotrophic lateral sclerosis, Parkinson's disease, or multiple sclerosis.

Replication

Frei et al published a study from Denmark, designed to test the Huss et al finding, which failed to replicate the finding.  This was one of the studies that led SCENIHR to conclude in their 2015 Opinion that

Only few new studies have been published since the previous Opinion. Although the new studies in some cases have methodological weaknesses, they do not provide support for the previous conclusion that ELF MF exposure increases the risk for Alzheimer's disease.

Am J Epidemiol. 2013 May 1;177(9):970-8.

Residential distance to high-voltage power lines and risk of neurodegenerative diseases: a Danish population-based case-control study.
Frei P, Poulsen AH, Mezei G, Pedersen C, Cronberg Salem L, Johansen C, Röösli M, Schüz J.

The aim of this study was to investigate the possible association between residential distance to high-voltage power lines and neurodegenerative diseases, especially Alzheimer's disease. A Swiss study previously found increased risk of Alzheimer's disease for people living within 50 m of a power line. A register-based case-control study including all patients diagnosed with neurodegenerative diseases during the years 1994-2010 was conducted among the entire adult population of Denmark. Using conditional logistic regression models, hazard ratios for ever living close to a power line in the time period 5-20 years before diagnosis were computed. The risks for developing dementia, Parkinson's disease, multiple sclerosis, and motor neuron disease were not increased in persons living within close vicinity of a power line. The risk of Alzheimer's disease was not increased for ever living within 50 m of a power line (hazard ratio = 1.04, 95% confidence interval: 0.69, 1.56). No dose-response according to number of years of living within 50 m of a power line was observed, but there were weak indications of an increased risk for persons diagnosed by the age of 75 years. Overall, there was little support for an association between neurodegenerative disease and living close to power lines.

Occupational studies of Motor Neurone Disease from the UK and the Netherlands

Two relatively recent studies have each looked at Motor Neurone Diases (MND) or its commonest type, Amyotrophic Lateral Sclerosis (ALS).  Both were occupational studies, looking at exposures in large cohorts of workers, one in the UK and one in the Netherlands.

The UK study was based just on workers in the electricity industry, and used exposure assessment methods that had been developed specifically for that industry.  The Netherlands study covered all workers, and used a less sophisticated Job-Exposure Matrix.  The UK study did not find associations; the Netherlands study did.

The abstracts of the two studies

Occup Med (Lond). 2014 Sep;64(6):454-60.
Neurodegenerative disease and magnetic field exposure in UK electricity supply workers.Sorahan T, Mohammed N. 

 

BACKGROUND: Previous research has suggested a possible link between neurodegenerative disease and exposure to extremely low-frequency electric and magnetic fields.

AIMS: To investigate whether risks of Alzheimer's, motor neurone or Parkinson's disease are related to occupational exposure to magnetic fields.

METHODS: The mortality experienced by a cohort of 73051 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-2010. All employees were hired in the period 1952-82, were employed for at least 6 months and had some employment after 1 January 1973. Detailed calculations had been performed by others to enable an assessment to be made of exposures to magnetic fields. Poisson regression was used to calculate relative risks (rate ratios) of developing any of the three diseases under investigation for categories of lifetime, distant (lagged) and recent (lugged) exposure.

RESULTS: No statistically significant trends were shown for risks of any of these diseases to increase with estimates of lifetime, recent or distant exposure to magnetic fields.

CONCLUSIONS: There is no convincing evidence that UK electricity generation and transmission workers have suffered elevated risks from neurodegenerative diseases as a consequence of exposure to magnetic fields.

Occup Environ Med 2017;0:1. doi:10.1136/oemed-2016-103780
Occupational exposure and amyotrophic lateral sclerosis in a prospective cohort
Tom Koeman, Pauline Slottje, Leo J Schouten, Susan Peters, Anke Huss, Jan H Veldink, Hans Kromhout, Piet A van den Brandt, Roel Vermeulen
Objective To prospectively study suspected occupational risk factors for amyotrophic lateral sclerosis (ALS).
Methods For this case–cohort analysis within the prospective Netherlands Cohort Study, 58 279 men and 62 573 women aged 55–69 years at enrolment in 1986 were followed up for 17.3 years on ALS mortality. Information on occupational history and potential
confounders were collected at baseline through a selfadministered questionnaire and entered for a random subcohort (2092 men and 2074 women) and ALS deaths (76 men and 60 women). Occupational exposure to solvents, pesticides, metals, extremely low frequency
magnetic fields (ELF-MFs) and electrical shocks was estimated by means of job exposure matrices (JEMs). Associations between ever/never occupationally exposed and cumulative exposure and ALS mortality were analysed by gender using Cox regression.
Results Occupational exposure to ELF-MF showed a possible association with ALS mortality among men: HR for ever holding a job with high exposure versus background 2.19 (95% (CI): 1.02 to 4.73) and HR for the highest tertile of cumulative exposure versus
background 1.93 (95% CI 1.05 to 3.55).
Interpretation These results strengthen the evidence suggesting a positive association between ELF-MF exposure and ALS. We did not replicate earlier positive findings for other occupational exposures.

 

Multiple Sclerosis

Multiple sclerosis has not been looked at as much as the other neurodegenrative disorders. We are aware of just one paper which concludes it found “no support” for an association with EMFs.

 

Neurology. 1999 Apr 12;52(6):1279-82.
Multiple sclerosis among utility workers

Johansen C, Koch-Henriksen N, Rasmussen S, Olsen JH.

Institute of Cancer Epidemiology, The Danish Cancer Society, Copenhagen. christof@cancer.dk

The incidence of MS was assessed in a nationwide cohort study of 31,990 employees of Danish utility companies between 1900 and 1993. Overall, 32 cases of MS were diagnosed, as compared with 23.7 expected from national incidence rates, to yield a standardized incidence ratio of 1.35 (95% confidence interval, 0.92 to 1.91). We found no support for the hypothesis of an association between occupational exposure to electromagnetic fields and the risk of MS.