Study type: Epidemiological study (observational study)

Association between Extremely Low-Frequency Electromagnetic Fields Occupations and Amyotrophic Lateral Sclerosis: A Meta-Analysis. epidem.

Published in: PLoS One 2012; 7 (11): e48354

Aim of study (acc. to author)

A meta-analysis was performed to evaluate the relationship between occupational exposure to extremely low-frequency magnetic fields and the risk of amyotrophic lateral sclerosis.

Further details

Following 17 studies were included in the pooled analysis: Deapen et al. (1986), Gunnarsson et al. (1991), Gunnarsson et al. (1992), Strickland et al. (1996), Davanipour et al. (1997), Savitz et al. (1988a), Savitz et al. (1988b), Johansen et al. (2000), Noonan et al. (2002), Feychting et al. (2003), Hakansson et al. (2003), Weisskopf et al. (2005), Park et al. (2005), Röösli et al. (2007), Sorahan et al. (2007), Fang et al. (2009), and Parlett et al. (2011).
Sub-analyses were conducted taking into account study design, exposure assessment method and diagnosis criteria. Among these seventeen studies, there were nine case-control studies and eight cohort studies. Seven studies assessed the exposure levels based on job title, five were based on the job-exposure matrix, and five were based on both. Six studies used clinical diagnosis, and the others used the death certificate for diagnosis of amyotrophic lateral sclerosis.

Endpoint/type of risk estimation

Type of risk estimation: (odds ratio (OR))




Study size

Type Value
Total 7,307,441

case-control studies: 9,506 cases and 4,946 controls; cohort studies: 7,292,989 persons and 3,175 cases

Statistical analysis method:

Conclusion (acc. to author)

Occupational exposure to extremely low-frequency magnetic fields was significantly associated with increased risk of amyotrophic lateral sclerosis in pooled studies (RR 1.29, CI 1.02-1.62), and case-control studies (OR 1.39, CI 1.05-1.84), but not cohort studies (RR 1.16, CI 0.80-1.69). In sub-analyses, similar significant associations were observed when the exposure level was defined by the job title, but not the job-exposure matrix. Furthermore, significant associations were found in studies of subjects who were clinically diagnosed but not those based on the death certificate.
The data suggest a slight but significant risk increase of amyotrophic lateral sclerosis among those with job titles related to relatively high levels of exposure to extremely low-frequency magnetic fields. Potential biases cannot be excluded. Electrical shocks or other unidentified variables associated with electrical occupations, rather than magnetic-field exposure, may be responsible for the observed associations with amyotrophic lateral sclerosis.

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