title: Amyotrophic lateral sclerosis among cross-country skiers in Sweden.
abstract: A highly increased risk of amyotrophic lateral sclerosis (ALS) has been suggested among professional athletes. We aimed to examine whether long distance cross-country skiers have also a higher risk of ALS and whether the increased risk was modified by skiing performance. We followed 212,246 cross-country skiers in the Swedish Vasaloppet cohort and a random selection of 508,176 general Swedes not participating in the Vasaloppet during 1989-2010. The associations between cross-country skiing as well as skiing performance (i.e., type of race, finishing time and number of races) and the consequent risk of ALS were estimated through hazard ratios (HRs) derived from Cox model. During the study, 39 cases of ALS were ascertained among the skiers. The fastest skiers (100-150% of winner time) had more than fourfold risk of ALS (HR 4.31, 95% confidence interval [CI] 1.78-10.4), as compared to skiers that finished at >180% of winner time. Skiers who participated >4 races during this period had also a higher risk (HR 3.13, 95% CI 1.37-7.17) than those participated only one race. When compared to the non-skiers, the fastest skiers still had a higher risk (HR 2.08, 95% CI 1.12-3.84), as skiers who had >4 races (HR 1.88, 95% CI 1.05-3.35), but those finishing at >180% of winner time had a lower risk (HR 0.46, 95% CI 0.24-0.87). In conclusion, long distance cross-country skiing is associated with a higher risk of ALS, but only among the best skiers; recreational skiers appear to have a largely reduced risk.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Box 281, 171 77, Stockholm, Sweden. fang.fang@ki.se.
authors.forename: Fang
authors.initials: F
authors.lastname: Fang
authors.affiliation: Department of Internal Medicine, Mora Hospital, Mora, Sweden.|Department of Medical Sciences, Cardiology, and Uppsala Clinical Research Center, Uppsala University, Uppsala, Sweden.
authors.forename: Ulf
authors.initials: U
authors.lastname: Hållmarker
authors.affiliation: Department of Medical Sciences, Cardiology, and Uppsala Clinical Research Center, Uppsala University, Uppsala, Sweden.
authors.forename: Stefan
authors.initials: S
authors.lastname: James
authors.affiliation: Department of Neurology, Karolinska University Hospital, Stockholm, Sweden.|Department of Clinical Neurosciences, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Caroline
authors.initials: C
authors.lastname: Ingre
authors.affiliation: Department of Surgical Sciences, Section of Orthopedics, Uppsala University, Uppsala, Sweden.
authors.forename: Karl
authors.initials: K
authors.lastname: Michaëlsson
authors.affiliation: Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Ahlbom
authors.affiliation: Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Maria
authors.initials: M
authors.lastname: Feychting
mesh_terms: D000328:Adult; D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000453:epidemiology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D016016:Proportional Hazards Models; D012865:Skiing; D013177:Sports; D013548:Sweden / Q000453:epidemiology
keywords: Amyotrophic lateral sclerosis; Cross-country ski; Longitudinal study; Physical activity