Dose-response relationship between exercise and respiratory disease mortality.

Pneumonia is the leading cause of death from infection in the United States, and in combination with influenza ranks eighth among all underlying causes of death [6,14]. Hospitalization is required for 40% to 50% of those infected, with approximately 10% requiring intensive care [24]. By 2020, the annual number of hospitalizations for community-acquired pneumonia is expected to rise to one million in the United States as the population ages [26]. In the elderly, the risk for community-acquired pneumonia is increased by heart disease, chronic lung disease, immunosuppressive drugs, alcoholism, and increasing age [9]. Long-term survival of community-acquired pneumonia is diminished by age, male sex, low educational achievement, and comorbid illnesses [14], with age and comorbid conditions being stronger predictors of survival than abnormal acute physiologic or laboratory findings [13]. Less common are nosocomical (hospital-acquired) and aspiration pneumonia. Treatment of nosocomical pneumonia is becoming increasingly problematic due to increases in antibiotic resistance of gram-negative bacteria [22], and has greater mortality (38% to over 70% [15]) than community-acquired pneumonia. Aspiration pneumonia, which is an infection of the lung caused by the inhalation of vomit or food, currently ranks as the fifteenth leading cause of death in the United States [6]. Its occurrence may indicate impaired ability to remove food or vomit by coughing due to age, inebriation, a complication of general anesthesia, or debilitation, as, for example, due to stroke [21]. Public health guidelines recommend 150 minutes a week of moderate-intensity, or 75 minutes a week of vigorous-intensity aerobic physical activity [20]. Multiple health benefits have been ascribed to physical activity [20]. However, these benefits do not currently include decreased respiratory disease risk. Two reports from the Nurses' Health Study II suggest that the risk for community-acquired pneumonia decreases with greater leisure-time and recreational physical activity in women, but not when adjusted for body mass index (BMI) [1,17], and, to our knowledge, there have been no significant risk reductions reported for men. However, reductions in pneumonia risk would be consistent with evidence suggesting that regular exercise improves immune function and attenuates its decline with age [3,7,8,11,12,19,35,37]. This report examines the association of running and walking with mortality due to respiratory disease in the National Walkers' and Runners' Health Studies, prospective epidemiological cohorts of over 150,000 walkers and runners whose mortality follow-up has been completed through 2008. The runners and walkers reported usual distance run or walked per week as part of their baseline questionnaire, which has been shown to be a superior to the more traditional time-based physical activity assessments for testing epidemiological hypotheses [32-34]. The large sample size, and the superior quantification of physical activity, provides a unique opportunity to test whether greater exercise energy expenditure predicts lower risk for respiratory diseases in general, and for pneumonia and aspiration pneumonia in particular.