b'Keep MovingA growing number of studies confirm that routinely engaging in physical activity can fortify your defenses. In a University of Washington study, women who walked regularly were three times less likely to catch colds as their sedentary counterparts were. Another study of almost 550 adults found that those who were moderately active had a 20 percent lower risk of developing an upper respiratory tract infection than their inactive colleagues did. Researchers suspect that exercise works both directly and indirectly to enhance the immune response:Physical activity helps flush bacteria out of the lungs and airways.Exercise enhances your bodys immune response by speeding up the antibodies and white blood cells in your blood stream so that they can detect harmful bacteria and viruses sooner. The brief rise in body temperature during and right after a good sweat session may prevent bacteria from growing. This temperature rise may also help the body fight infection more effectively. Exercise slows down the release of cortisol and other stress-related hormones that can make you more vulnerable to illness. Preliminary research in the journal Biological Psychiatry suggests that chronic stress may alter how white blood cells function, leaving them less responsive to inflammation and illness.Although working out is good for you, be careful not to overdo it. Heavy, long-term exercise like taking part in a marathon or triathlete competition could actually decrease the number of white blood cells circulating through the body. And research shows that prolonged moderate to high intensity 12OPTIMAL IMMUNIT Y'