During moderate exercise several transient changes occur in the immune system.29, 51, 52 and 53 Moderate exercise increases the recirculation of immunoglobulins, and neutrophils and natural killer cells, two cells that play a critical role in innate immune defenses. Animal data indicate that lung macrophages play an important role in mediating the beneficial effects of moderate exercise on lowered susceptibility to infection.54 Stress hormones, which can suppress immunity, and pro- and anti-inflammatory cytokines, indicative 20s Proteasome activity of intense metabolic activity, are not elevated during moderate exercise.29 Although the immune system returns to pre-exercise levels within a few hours after the exercise session

is over, each session may represent an improvement in immune surveillance

that reduces the risk of infection over the long term. Other exercise-immune related benefits include enhanced antibody-specific responses to vaccinations. For example, several studies indicate that both acute and chronic moderate exercise training improves the body’s antibody response to the influenza vaccine.55, 56, 57 and 58 In one study, a 45-min moderate exercise bout just before influenza vaccination improved the antibody response.55 These data provide additional evidence that moderate exercise favorably influences overall immune surveillance against pathogens. Taken together, the data on the relationship phosphatase inhibitor library between moderate exercise, enhanced immunity, and lowered URTI risk are consistent with guidelines urging the general public to engage in near-daily brisk walking. Although methodology varies widely and evidence is still emerging59 epidemiologic and randomized exercise training studies consistently report a reduction in URTI incidence or risk of 18%–67%. This is the most important finding that has emerged from exercise immunology studies during the past two decades. Animal and human data indicate that during each exercise bout, transient immune changes take place that over time may improve immunosurveillance against pathogens,

thereby reducing URTI risk. The magnitude of reduction in URTI risk with near-daily moderate physical activity exceeds levels reported for most medications and supplements, and bolsters public health guidelines urging individuals to be physically active until on a regular basis. Regular physical activity should be combined with other lifestyle strategies to more effectively reduce URTI risk. These strategies include stress management, regular sleep, avoidance of malnutrition, and proper hygiene.33, 60, 61, 62 and 63 URTI is caused by multiple and diverse pathogens, making it unlikely that a unifying vaccine will be developed.33 Thus lifestyle strategies are receiving increased attention by investigators and public health officials, and a comprehensive lifestyle approach is more likely to lower the burden of URTI than a focus on physical activity alone.