Want to boost your immune system? Ward off colds and flus? One of the most proven methods is also safe, simple and free: exercise! Exercise increases leukocyte (white blood cell) production. White blood cells are the body’s main defense against bacterial and viral infections.

Even modest exercise, such as a daily 30 minute walk, works to increase the level of leukocytes if done regularly. And more is better! Conversely, non-exercisers have a higher risk of infections, including colds and flus, compared to those who exercise.