Exercise increases fitness, supports weight loss, and boosts the immune system. Wait—boosts the immune system? Sure, we’ve all heard this, but how many of us have experienced otherwise?

R.J. Simpson et al. of the Laboratory of Integrated Physiology, Department of Health and Human Performance at the University of Houston reported in their abstract for “Exercise and the aging immune system” that regular exercise enhanced vaccination responses, positively affected white blood cell health, decreased age-related inflammation, and increased cells’ ability to continue reproducing thus increasing one’s lifespan. “This contention,” explain Simpson et al., “is supported by the majority of animal studies that report improved immune responses and outcomes to viral infections and malignancies due to exercise training.”

In a University of Tennessee, Knoxville study, “Physical Activity and Immunity in HIV-Infected Individuals,” C. M. Bopp et al. also found “that regular physical activity may also be beneficial for HIV patients.”

In the study “Moderate to vigorous physical activity and risk of upper-respiratory tract infection,” printed in the August 2002 issue of Medicine & Science in Sports & Exercise, Charles E. Matthews et al. demonstrated that “moderate levels of physical activity are associated with a reduced risk for upper-respiratory tract infection. Risk was reduced by about 20% in men and women.”

Why Do Athletes Get Sick after Starting a New Exercise Routine?

Countless studies support the idea that exercise boosts the immune system, but what about those of us who consistently come down with upper respiratory tract infections shortly after committing to a new exercise routine? After three weeks of faithful commitment to my mountain bike, I sit at home trying to recover from a persistent cold so I can get back into the swing of things. This is not unusual. Every time I commit to a workout routine, I get sick.

In her article, “Outrun The Common Cold,” published by Runner’s World in December 2007, Jennifer Pirtle reports, “Most data cite immune boosts after 30 to 75 minutes of moderate activity.” Not too many mountain bikers ride for only 75 minutes. So what happens when you ride for the usual 90 or 120 minutes? What about your three-hour rides?

David Nieman, DrPH, director of the Appalachian State University Human Performance Laboratory—and endurance runner—has focused on exercise immunology over the past 20 years. In the study, “Nutritional strategies to counter stress to the immune system in athletes, with special reference to football,” Dr. Nieman and Nicolette C. Bishop describe an ‘open window’ of immune dysfunction possibly lasting between three and 72 hours in which illness is most likely to develop. “Ingestion of carbohydrate beverages during intense and prolonged exercise has emerged as the most effective [countermeasure]. However, carbohydrate supplementation during exercise decreases exercise-induced increases in plasma cytokines and stress hormones, but is largely ineffective against other immune components including natural killer cell function and salivary IgA.” IgA is also found in blood and tears and is an immunoglobulin in the membranes of the ears, eyes, nose, and mouth that is responsible for protecting those common viral and bacterial entry points from such foreign bodies.

Preventing Illness after Endurance Workouts

This certainly makes the case for increased carbohydrate consumption during exercise, preferably in fluid form since the carbohydrates are delivered faster than solid carbohydrates such as those in bagels and bananas, but it doesn’t go far enough to prevent infection during the susceptible 72-hour period following an endurance workout. This is where lifestyle factors come into play: improve immune health by scheduling adequate sleep into your schedule, eat plenty of antioxidants and anti-inflammatory foods, and incorporate stress-reduction techniques into your day.

In addition to sleep, diet, and stress reduction, it is important to prevent exposure of your mucosal membranes to pathogens. Do not touch your eyes, ears, nose, or mouth after touching foreign surfaces that are highly likely to expose you to viruses and bacteria, such as gas pumps, shopping carts, door handles, and even pens at your local restaurants or banks. Instead, carry an alcohol-based hand sanitizer to use after exposure to any of these types of surfaces.