The average adult has two to three upper respiratory infections each year. We are exposed to viruses all day long, but some people seem more susceptible to catching colds or the flu. The following factors have all been associated with impaired immune function and increased risk of catching colds:
Regular Moderate Exercise Boosts ImmunityThere are some things that seem to protect us from catching colds and the flu. One of those things appears to be moderate, consistent exercise. Research continues to support a link between moderate, regular exercise and a healthy immune system.
Early studies found that recreational exercisers reported fewer colds once they began running regularly. Moderate exercise has been linked to a positive immune system response and a temporary boost in the production of macrophages, the cells that attack bacteria. It is believed that regular, consistent exercise can lead to substantial benefits in immune system health over the long-term.
More recent studies have shown that there are physiological changes in the immune system as a response to exercise. During moderate exercise immune cells circulate through the body more quickly and are better able to kill bacteria and viruses. After exercise ends, the immune system generally returns to normal within a few hours, but consistent, regular exercise seems to make these changes a bit more long-lasting.
According to professor David Nieman, Dr. PH., of Appalachian State University, when moderate exercise is repeated on a near-daily basis there is a cumulative effect that leads to a long-term immune response. His research showed that those who walk at 70-75 percent of their VO2 Max for 40 minutes per day had half as many sick days due to colds or sore throats as those who don't exercise.
Too Much Exercise May Decrease ImmunityHowever, there is also evidence that too much intense exercise can reduce immunity. This research is showing that more than 90 minutes of high-intensity endurance exercise can make athletes susceptible to illness for up to 72 hours after the exercise session. This is important information for those who compete in longer events such as marathons or triathlons.
Intense exercise seems to cause a temporary decrease in immune system function. Research has found that during intense physical exertion, the body produces certain hormones that temporarily lower immunity.
Cortisol and adrenaline, known as the stress hormones, raise blood pressure and cholesterol levels and suppress the immune system. This effect has been linked to the increased susceptibility to infection in endurance athletes after extreme exercise (such as marathon running or Ironman-distance triathlon training).
If you are training for ultra-endurance events, a key component of your training should be including enough rest and recovery days to allow your body (immune system) to recover. If you are feeling run-down or have other symptoms of overtraining syndrome --such as increased resting heart rate, slower recovery heart rate, irritability or general heaviness and fatigue -- you may need to tone down your workouts as well.
If you are already ill, you should be careful about exercising too intensely. Your immune system is already taxed by fighting your infection, and additional stress could undermine your recovery. In general, if you have mild cold symptoms and no fever, light or moderate exercise may help you feel a bit better and actually boost your immune system. Intense exercise will only make things worse and likely extend your illness.
Psychological Stress Also Reduces ImmunityIt's not only physical stress that increases the release of cortisol and adrenaline. Psychological stress can also impair immunity and lead to an increase of cold and flu infections.
Researchers at Ohio State followed people who had the stress of caring for a loved one with Alzheimer's disease and found that they experienced twice as many colds as non-caregivers. For such individuals, there is clearly a physical benefit to moderate, regular exercise.
Moderate exercise is not the only way to avoid colds and other infections. For more ways to stay healthy check out these tips for avoiding germs at the gym.
Acute exercise stimulates macrophage function: possible role of NF-kappaB pathways. Cell Biochemistry and Function. 2006 Aug 14;
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Nieman DC, Henson DA, Austin MD, Brown VA. The immune response to a 30-minute walk. Med Sci Sports Exerc 37:57-62, 2005. David Nieman, of Appalachian State University
Nieman DC. Risk of Upper Respiratory Tract Infection in Athletes: An Epidemiologic and Immunologic Perspective. Journal of Athletic Training 1997 Oct.