This article originally appeared in Shape.

Take a deep breath. That simple act can help bolster your immunity. Start huffing and puffing during a workout, and that will improve it too. The lungs and heart power the many pathways of immunity, which is why the way you breathe and your overall cardiorespiratory fitness are key.

Your lungs move oxygen-rich blood to the heart via capillaries, and then your heart extracts oxygen from the blood and pumps it around your body, like to the muscles you're contracting as you walk or cycle or squat, says Benjamin Levine, M.D., an exercise science professor at University of Texas Southwestern Medical Center in Dallas. That boost in muscle movement and oxygen flow also sparks the increased circulation of immune cells. Exercise trains your heart and lungs to pump oxygen-rich blood more efficiently and, by extension, send more immune cells into active duty. (More here: How Exercise Can Boost Your Immune System)

But focusing on your breath even as you're sitting still helps. When you inhale and exhale fully and slowly, you turn on our parasympathetic system — the calming lever of our nervous system, says Susan Blum, M.D., the author of The Immune System Recovery Plan (Buy It, $15, (The message is sent via the vagus nerve, which runs from the brain stem through the lungs and heart and into the diaphragm and intestines.) Flipping the switch likewise deactivates the sympathetic nervous system, our fight-or-flight response that pumps out stress hormones, like cortisol and adrenaline, says Thomas W. Decato, M.D., a pulmonologist in Spokane, Washington.