Mixed
Moderate exercise training (≥5 days/week, 20+ min bouts) significantly reduces the incidence and duration of upper respiratory tract infections (URTI) compared to sedentary behavior.
Aim for at least 20 minutes of moderate aerobic activity, five days a week. This level of activity is proven to cut your risk of getting sick by nearly half compared to being sedentary, and it does so without the immune suppression risks associated with extreme endurance training.
The RCTs (8 weeks to 1 year in length) are consistent in demonstrating that study participants assigned to moderate exercise programs experience reduced URTI incidence and duration. The magnitude of reduction in URTI symptom days with near-daily moderate exercise in these RCTs (typically 40%–50%) exceeds levels reported for most medications and supplements...
Why this rating
Supported by multiple RCTs and large epidemiological studies, though the paper notes the right side of the J-curve (high intensity) is less clear for elite athletes.
Source
The compelling link between physical activity and the body's defense system
David C. Nieman et al. · Journal of sport and health science/Journal of Sport and Health Science · 2018
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