The average adult has two to three upper respiratory infections each year. We are exposed to bacteria all day long, but some people seem more susceptible to catching the bug. The following factors have all been associated with impaired immune function and increased risk of catching colds.
- old age
- cigarette smoking
- poor nutrition
- fatigue and lack of sleep
However, there are also some things that seem to protect us from picking up colds. One of those things seems to be moderate, consistent exercise. More and more research is finding a link between moderate, regular exercise and a strong immune system.
Early studies reported that recreational exercisers reported fewer colds once they began running. More recent studies have shown that there are physiological changes in the immune system response to exercise.
During moderate exercise immune cells circulate through the body more quickly, and are better able to kill bacteria and viruses. After the exercise ends, the immune system returns to normal within a few hours. However, consistent, regular exercise seems to make these changes a bit more long-lasting. According to professor David Nieman 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 of their maximum heart rate 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 Can Backfire
However, there is also evidence that too much intense exercise can reduce immunity. This research is finding 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.