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Title: Smoking and risk of amyotrophic lateral sclerosis: a pooled analysis of 5 prospective cohorts.
Authors: Wang H,  O'Reilly ÉJ,  Weisskopf MG,  Logroscino G,  McCullough ML,  Thun MJ,  Schatzkin A,  Kolonel LN,  Ascherio A
Journal: Arch Neurol
Date: 2011 Feb
Branches: NEB
PubMed ID: 21320987
PMC ID: PMC3319086
Abstract: BACKGROUND: Cigarette smoking has been proposed as a risk factor for amyotrophic lateral sclerosis (ALS), but epidemiological studies supporting this hypothesis have been small and mostly retrospective. OBJECTIVE: To prospectively examine the relation between smoking and ALS in 5 well-established large cohorts. DESIGN: Five prospective cohorts with study-specific follow-up ranging from 7 to 28 years. SETTING: Academic research. PATIENTS: Participants in 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 (formerly known as the American Association of Retired Persons) Diet and Health Study. MAIN OUTCOME MEASURES: Amyotrophic lateral sclerosis deaths identified through the National Death Index. In the Nurses' Health Study and the Health Professionals Follow-up Study, confirmed nonfatal incident ALS was also included. RESULTS: A total of 832 participants with ALS were documented among 562,804 men and 556,276 women. Smokers had a higher risk of ALS than never smokers, with age- and sex-adjusted relative risks of 1.44 (95% confidence interval, 1.23-1.68; P < .001) for former smokers and 1.42 (95% confidence interval, 1.07-1.88; P = .02) for current smokers. Although the risk of ALS was positively associated with pack-years smoked (P < .001), duration of smoking (9% increase for each 10 years of smoking, P = .006), and the number of cigarettes smoked per day (10% increase for each increment of 10 cigarettes smoked per day, P < .001), these associations did not persist when never smokers were excluded. However, among ever smokers, the risk of ALS increased as age at smoking initiation decreased (P = .03). CONCLUSIONS: Results of this large longitudinal study support the hypothesis that cigarette smoking increases the risk of ALS. The potential importance of age at smoking initiation and the lack of a dose response deserve further investigation.