authors of both studies conclude that physical activity is unlikely to be a major contributor to ALS risk (Veldink et al. 2005; Longstreth et al. 1998). Veldink et al. also reported on a systematic review of 24 studies published from 1966 to 2003. They found that most studies were methodologically weak and that all studies that had reported a relationship between physical activity and ALS had less than rigorous designs.
A recent study of 7,325 male Italian professional football (soccer) players over the period 1970–2003 revealed an increased incidence of ALS relative to what would have been expected given ALS incidence in the general population in Italy (Chio et al. 2005). Five cases were identified among the players compared with 0.77 expected from age- and sex-specific rates in the general population (standardized mortality ratio, 6.5; 95% CI, 2.1–15.1). The authors also reported an increased risk associated with number of years as a professional soccer player (≤5 years: standardized incidence ratio [SIR], 3.5; 95% CI, 0.4–12.7; >5 years: SIR, 15.2; 95% CI, 3.1–44.4).
A case-control study of 110 newly diagnosed ALS patients from two centers in New England and 210 population-based controls examined demographic characteristics, family history of ALS, and histories of smoking and alcohol consumption (Kamel et al. 1999). With adjustment for age, sex, region, and education, “ever smoking” was associated with a 70% increase in ALS risk (OR, 1.7; 95% CI, 1.0–2.8). “Current smoking” was not found to be associated with ALS (OR, 0.9; 95% CI, 0.4–1.8), but risk was increased among those who reported having stopped smoking more than 5 years before the time of the interview (OR, 1.9; 95% CI, 1.1–3.3) and even more among those who had quit within the last 5 years (OR, 4.2; 95% CI, 1.7–10.7). Increases in risk were reported for every stratum of “cigarettes per day,” “years smoked,” and “pack-years”; a statistically significant trend (p=0.046) was observed in connection with “cigarettes per day.” In contrast, ever having used alcohol was not associated with increased ALS risk (OR, 1.1; 95% CI, 0.4–3.2). A weak and imprecisely estimated increase was noted among those who reported more than 31 drinks