Getting regular exercise strengthens muscles and conditions our hearts, and it may also bolster the immune system enough to help us ward off colds and flu. A study from South Korea examined this potential benefit in mice. The researchers reasoned that inflammatory compounds produced in fat cells can weaken the immune system’s response to illness or infection. However, exercise can reduce the number and size of fat cells and thus potentially lower levels of inflammation. To test whether physical activity can actually have that effect, the researchers compared the results of infection with Staphylococcus bacteria in mice that exercised and those that didn’t. They divided laboratory mice into two groups. Those in one went about their usual activities, while those in the other group exercised by swimming. Because they’re not natural swimmers, the mice expended a great deal of energy staying afloat. Even though the strain on their muscles promoted some inflammation, the exercise also led to fewer and smaller fat cells. After putting the mice through the exercise, the researchers inoculated half the swimmers and half the sedentary mice with Staphylococcus. All the infected mice became ill, but the swimmers had lower levels of pro-inflammatory cells and their bodies produced greater numbers of immune system cells capable of fighting the infection. Would this effect be reproducible in humans? The Korean researchers think so.
My take? These findings may help explain how aerobic exercise strengthens the immune system. We know that exercise conditions our hearts and arteries and respiratory systems, increases stamina and general fitness. It also promotes cleansing of the blood by stimulating circulation and perspiration, and leads to a sense of well being, in part by releasing endorphins, the opiate-like molecules in the brain that can make us high, happy, and more tolerant of discomfort. Physical activity also increases the flow of oxygen to all organs, enabling them to work more efficiently. It burns calories, reduces stress, lowers serum cholesterol and tones the nervous system. Given its positive impact on the entire body, it makes sense that exercise would also help us fight off colds and flu.