Wednesday, February 25, 2015

Risk factors for amyotrophic lateral sclerosis

Risk factors for amyotrophic lateral sclerosis

Ingre C, Roos PM, Piehl F, Kamel F, Fang F. Risk factors for amyotrophic lateral sclerosis.Clin Epidemiol. 2015 Feb 12;7:181-93. doi: 10.2147/CLEP.S37505. eCollection 2015.


Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease. It is typically fatal within 2-5 years of symptom onset. The incidence of ALS is largely uniform across most parts of the world, but an increasing ALS incidence during the last decades has been suggested. Although recent genetic studies have substantially improved our understanding of the causes of ALS, especially familial ALS, an important role of non-genetic factors in ALS is recognized and needs further study. In this review, we briefly discuss several major genetic contributors to ALS identified to date, followed by a more focused discussion on the most commonly examined non-genetic risk factors for ALS. We first review factors related to lifestyle choices, including smoking, intake of antioxidants, physical fitness, body mass index, and physical exercise, followed by factors related to occupational and environmental exposures, including electromagnetic fields, metals, pesticides, β-methylamino-L-alanine, and viral infection. Potential links between ALS and other medical conditions, including head trauma, metabolic diseases, cancer, and inflammatory diseases, are also discussed. Finally, we outline several future directions aiming to more efficiently examine the role of non-genetic risk factors in ALS.
Open Access:

Workers in various occupations with seemingly disparate exposures have been reported to be potentially at altered risk of ALS, including athletes, carpenters, cockpit workers, construction workers, electrical workers, farm workers, hairdressers, house painters, laboratory technicians, leather workers, machine assemblers, medical service workers, military workers, nurses, power production plant workers, precision metal workers, programmers, rubber workers, shepherds, tobacco workers, veterinarians, and welders.124,125 These occupations potentially involve work exposures to chemicals, pesticides, metals, and electromagnetic fields (EMF).125–127 However, common denominators among these different occupations are not easily identified.

Military personnel are exposed to a battery of unique and potentially harmful factors, including physical and psychological exertion and trauma, transmissible agents (eg, viruses) and vaccines, toxic substances (eg, heavy metals and chemicals), and other environmental toxicants specific to particular deployment areas. A review article focusing on the potential links between military-related factors and ALS has been published recently, and concluded that although there is evidence suggesting a role of military service in ALS, it is too premature to draw a firm conclusion regarding a causal relationship.128

Electric occupation, electric shock, and electromagnetic field

ALS has been associated with “electrical” occupations,129,130 especially welding.131 Magnetic fields, electrical fields, contact currents, microshocks, and both perceptible and imperceptible electric shocks all contribute to occupational exposure to extremely low frequency EMF. The reported association of ALS with EMF is generally weaker than that with electrical occupations.129,130 Evidence is not yet available to distinguish whether electric shocks or exposure to EMF underlies the association between electrical occupation and ALS.132–134 A meta-analysis suggested that there might be a slight but statistically significant increase in ALS risk among people with job descriptions related to relatively high levels of EMF exposure.135 However, studies using residential proximity to power lines as a proxy for EMF exposure have failed to support such a relationship.136,137 Different exposure levels investigated in studies of occupational, compared with residential, exposure to EMF may partly explain the different findings to date.


Joel M. Moskowitz, Ph.D., Director
Center for Family and Community Health
School of Public Health
University of California, Berkeley

Electromagnetic Radiation Safety

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