Clinical and epidemiological data suggest that strenuous exercise increases the incidence of upper respiratory tract infections (URTI) in athletes. However, little is known if the risk for URT infections is associated with the type of sports performed (e.g., endurance vs. strength exercise, or mixed sports) or whether accompanying lifestyle factors such as dietary behavior, daily stress, and the intake of nutritional supplements or immunostimulants influence the incidence of URT infections. In order to increase our knowledge on such questions, 852 athletes who attended our outpatient department for sports medicine filled out a retrospective questionnaire (1-year self-recalled) dealing with the following questions: number of URTI episodes in the last 12 months; number of training days lost due to URTI; type of exercise (endurance/power/mixed type/swimming); training extent; special procedures for regeneration (e.g., physiotherapy); lifestyle and daily stress; dietary behavior; intake of nutritional supplements; and use of immunostimulants. Of the respondents, 72.1% reported one or more URTI episodes in the last 12 months. In a multiple-regression model, the following variables were positive predictors of an URTI episode: endurance sports [odds ratio, 2.15; CI (95%), 1.51-3.06; p < .000], daily stress [odds ratio, 1.97; CI (95%), 1.26-3.08; p < .01], sleep deprivation [odds ratio, 1.69; CI (95%), 1.14-2.5; p < .01], female gender (odds ratio, 1.5; CI [95%] 1.05-2.13; p < .05), training extent in hour per week [odds ratio, 1.05; CI (95%), 1.02-1.08; p < .01), and diet control [odds ratio, 0.6; CI (95%), 0.37-0.82; p < .01]. The positive predictive value of this model for URTI episodes was 76%. Subgroup analysis revealed that in athletes exhibiting the highest rate of infections, use of immunostimulants reduced the number of training days lost (2 days) due to infections. In conclusion, both sports-specific items as well as lifestyle variables contribute substantially in explaining the risk for athletes to develop respiratory infections. These findings should be considered in sports-specific training regimes, particularly in athletes prone to URT infections.
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