DEAR DOCTOR: One of the yoga teachers at our gym always goes on and on about the importance of the vagus nerve whenever we do deep-breathing exercises to relax. What is she talking about, and why is it important?
DEAR READER: Your yoga instructor is referring to one of the attributes of the ever-fascinating vagus nerve, which is the most complex of the 12 cranial nerves. Like each of the cranial nerves, the vagus nerve arises directly from the brain rather than the spinal cord. It's the longest of these nerves, and it travels a meandering path through the body, beginning in the brain, through the face, neck and upper body, and to the abdomen, where it ends in the colon. In fact, its name derives from the Latin word for "wandering."
Along the way, the vagus nerve divides, branches out and exchanges fibers with numerous other nerves, thus playing a role in an impressive array of our sensory and motor functions. It's one of the crucial links between the brain and the neck, lungs, heart and abdomen, and it helps to regulate mood, heart rate, digestion, anti-inflammatory and immune response. The gut and brain communicate via the vagus nerve, as do many other parts of the body.
There's so much to tell about this remarkable structure that we could easily fill several columns and not scratch the surface. So let's get right to your question about the vagus nerve and deep breathing.
One of the functions of the vagus nerve is to communicate with the diaphragm. That means that when you're taking the slow, deep and controlled breaths associated with yoga, which engage the muscles of the abdomen and the diaphragm, you're stimulating the vagus nerve. And since vagal stimulation has been found to help lift mood, lessen anxiety and even lower blood pressure, it follows that you can trigger this relax-and-restore response by doing some deep breathing exercises.
What's great about diaphragmatic deep breathing is that it's portable. You can do it anywhere, at any time, without any special equipment. And the bonus is that you can practice it in public without anyone knowing you're doing it. If you have a home-based blood pressure device, you can do your own experiment about the benefits. Start by taking a baseline blood pressure reading without any special preparation. Follow this with a few minutes of diaphragmatic breathing. For anyone who has never tried it, it's slow, deep breaths that fill the lungs from bottom to top. Be sure to relax and soften the muscles of the belly, which will pop out a bit as you breathe, to get the full beneficial effect.
Holding the breath for five to 10 seconds also stimulates the vagus nerve. So does adding a bit of resistance to the exhale, which can be achieved by blowing out through pursed lips. Not only do these breathing techniques have the potential to impart a sense of calm and relaxation, they quiet the fight-or-flight response in our bodies. And as you'll see if you try the blood pressure monitor experiment, they will often yield a lower blood pressure reading.
Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health.