Moderate Exercise Boosts Immunity, But Marathons Could Make You Sick

We've all heard that exercise can help stave off illness by offering an immune system boost, but what kind of activity is best? According to one expert who surveyed the research, moderate exercise - things like taking a brisk walk or playing touch football with friends - can reduce our risk of getting colds and flu viruses. But in a case of "less is more," the same is not true of prolonged, intensive training, like the kind undertaken by marathon runners and elite athletes. Unlike an average workout, a marathon can actually increase the likelihood that an athlete will get sick. ...