As if there wasn’t already enough reasons not to light up, a new study in the February Archives of Neurology reports that smoking boosts one’s risk of amyotrophic lateral sclerosis (ALS) by a factor of 1.4. The study, led by Hao Wang at the Harvard School of Public Health, considered more than a million people from five different prospective studies, 832 of whom had ALS. The younger people started smoking, the higher their risk of this motor neuron disease.

Smoking has long been considered a possible ALS risk factor (Kamel et al., 1999). However, recent results are conflicting. Some studies say smoking is a risk factor (Binazzi et al., 2009; Gallo et al., 2009); others say it is not (Schmidt et al., 2010; Okamoto et al., 2009), and some say it is, but only in women (Alonso et al., 2010; Alonso et al., 2010).

In the current work, Wang and colleagues pooled data from five long-running prospective studies: the Nurses’ Health Study, the Health Professionals Follow-up Study, the Cancer Prevention Study II Nutrition Cohort, the Multiethnic Cohort, and the National Institutes of Health—AARP Diet and Health Study. The authors note that, unlike studies that recruit participants at ALS clinics, this method is likely to represent a more complete spectrum of people with ALS. Using death records, the researchers determined that 832 of the 1.1 million participants in the studies likely died of ALS. Those who smoked were more likely to die of the disease. There was no significant gender effect.

The authors suggest that nitric oxide or other cigarette ingredients might damage nerves or cause oxidative stress, which is often linked to ALS. Given that the earlier a person tried that first cigarette, the higher his or her risk, “one possibility is that early smoking starts a cascade of events in susceptible individuals,” wrote study coauthor Eilis O’Reilly of the Harvard School of Public Health in an e-mail to ARF.

“I don’t think this closes the debate,” added coauthor Marc Weisskopf, also at Harvard, in another e-mail, noting there are still further questions about how smoking and ALS relate. Conversely, Carmel Armon, who in 2009 concluded smoking is a clear risk factor for ALS (Armon, 2009) and was not involved in the current work, wrote in an e-mail that he sees no reason for further research. “There has to be a point where we accept the facts as they are,” he wrote.—Amber Dance


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Paper Citations

  1. . Association of cigarette smoking with amyotrophic lateral sclerosis. Neuroepidemiology. 1999;18(4):194-202. PubMed.
  2. . An exploratory case-control study on spinal and bulbar forms of amyotrophic lateral sclerosis in the province of Rome. Amyotroph Lateral Scler. 2009 Oct-Dec;10(5-6):361-9. PubMed.
  3. . Smoking and risk for amyotrophic lateral sclerosis: analysis of the EPIC cohort. Ann Neurol. 2009 Apr;65(4):378-85. PubMed.
  4. . Association of ALS with head injury, cigarette smoking and APOE genotypes. J Neurol Sci. 2010 Apr 15;291(1-2):22-9. PubMed.
  5. . Lifestyle factors and risk of amyotrophic lateral sclerosis: a case-control study in Japan. Ann Epidemiol. 2009 Jun;19(6):359-64. PubMed.
  6. . Smoking and the risk of amyotrophic lateral sclerosis: a systematic review and meta-analysis. J Neurol Neurosurg Psychiatry. 2010 Nov;81(11):1249-52. PubMed.
  7. . Association of smoking with amyotrophic lateral sclerosis risk and survival in men and women: a prospective study. BMC Neurol. 2010;10:6. PubMed.
  8. . Smoking may be considered an established risk factor for sporadic ALS. Neurology. 2009 Nov 17;73(20):1693-8. PubMed.

Further Reading


  1. . Monitoring systemic oxidative stress in an animal model of amyotrophic lateral sclerosis. J Neurol. 2011 May;258(5):762-9. PubMed.
  2. . TDP-43 proteinopathy and motor neuron disease in chronic traumatic encephalopathy. J Neuropathol Exp Neurol. 2010 Sep;69(9):918-29. PubMed.
  3. . Head injury and amyotrophic lateral sclerosis. Am J Epidemiol. 2007 Oct 1;166(7):810-6. PubMed.
  4. . A cluster of amyotrophic lateral sclerosis in New Hampshire: a possible role for toxic cyanobacteria blooms. Amyotroph Lateral Scler. 2009;10 Suppl 2:101-8. PubMed.
  5. . Population-based case-control study of amyotrophic lateral sclerosis in western Washington State. I. Cigarette smoking and alcohol consumption. Am J Epidemiol. 2000 Jan 15;151(2):156-63. PubMed.

Primary Papers

  1. . Smoking and risk of amyotrophic lateral sclerosis: a pooled analysis of 5 prospective cohorts. Arch Neurol. 2011 Feb;68(2):207-13. PubMed.