Epidemiological Studies on Long Distance Cross-Country Skiers : Participants in the Vasaloppet 1955-2010

Abstract: The overall aim of this thesis was to study the influence of physical activity on health. Risks and benefits of physical activity is of particular interest since there is a global trend of less physical activity among youths and adults.In order to investigate this aim we used a database from a large cross country ski race, Vasaloppet, with participants with a wide age range, and with both elite athletes and ordinary people who exercise and promote their health. The most serious risk of strenuous exercise is sudden death and it is challenging to identify preventive effects of major endemic diseases.Using epidemiological methodology we studied 200 000 Vasaloppet skiers and compared them with the general population. Based on personal identification numbers we added data from Swedish national personal and health registers, clinical registers as the cancer register, Swedeheart, or Swedish stroke register, and socioeconomic information from Statistics Sweden. In the Vasaloppet database we collected data on age, gender, finish time and number of races during the period 1989 to 2010.We evaluated risk of death during the race in two papers (I,II). During 90 years of annual races, cardiac arrest occurred in 20 skiers, of which five survived. The death rate is in average two per 100 000 skiers.We also studied the association with cancer incidence (paper III). The overall reduction of cancer was modest among skiers compared with the general population, but for cancers related to lifestyle the risks were markedly lower.We investigated the risk for recurrent myocardial infarction and found a 30% reduction among skiers (paper IV). In paper V we showed that skiers with a first stroke have a lower incidence of all-cause death. The skiers had a higher frequency of atrial fibrillation but had less severe stroke and no increased risk of recurrent stroke. Thus our data suggest that a lifestyle with a high level of physical activity may work as a protection after a cardiovascular event.Summary: The short excess mortality in endurance physical activity is by far outweighed by the long term protective effect of exercise in cardiovascular diseases and cancer.