The Science of Breathing for Stress Relief and Improved Health

Liz Lee
Nov 10
4 min read

I love science and I love learning. And, I am currently training to be a Certified Breath Coach, which will not only support my own nervous system regulation, but also help support my meditation practice and teaching. This blog is a deep dive into the 'respiratory' body, what happens when we breathe and why it is important for our overall health. As always, I infuse evidence from scientific literature, which you can read along with as you wish.

What Happens When We Breathe

When we breathe, the respiratory and circulatory systems exchange gases that keep our cells alive and regulate physiological balance.

1. Inhalation (Breathing In)

The diaphragm contracts and moves downward, expanding the chest cavity and drawing air into the lungs through the nasal or oral passages, trachea and bronchi, to the half a billion alveoli, where gas exchange occurs (Levitzky, 2013; West, 2012).
Oxygen diffuses from the alveoli into pulmonary capillaries and binds to hemoglobin in the blood, supplying oxygen to tissues for cellular respiration and ATP production. ATP - adenosine triphosphate is the energy source for all cellular activities in the body. (Guyton & Hall, 2021).

2. Exhalation (Breathing Out)

The diaphragm relaxes and moves up, decreasing lung volume and expelling carbon dioxide (CO₂), which is vital for maintaining the blood’s acid–base balance (Guyton & Hall, 2021).
- The lungs regulate acid-base balance by controlling the amount of CO₂ (which is acidic) in the blood. When CO₂ levels rise, breathing rate increases to expel it and reduce acidity. Being too acidic causes serious health problems, including neuronal responses in the brain. (Putnam, 2004).

Why Breathing Through the Nose Helps Calm Us

For the most part, the nose is for breathing, and the mouth is for eating and talking, and some forms of exercise. That is not to say you cannot breathe through your mouth, but for the purpose of regulation through the nose is considered the best.

When trying to calm ourselves (e.g., during stress or anxiety), nasal breathing has measurable physiological advantages because it activates the parasympathetic nervous system (PNS) and supports optimal gas exchange. Some of the science below...

1. Activates the Parasympathetic Nervous System (PNS)

Slow nasal breathing stimulates the vagus nerve, which lowers heart rate and blood pressure, promoting relaxation (Gerritsen & Band, 2018).
This helps shift the autonomic balance from sympathetic (“fight or flight”) dominance to parasympathetic (“rest and digest”) activity (Porges, 2011).

2. Nasal Breathing Produces Nitric Oxide (NO)

The nasal passages generate nitric oxide, a gas that improves blood flow, oxygen absorption, and neural oxygenation (Lundberg, Weitzberg, & Gladwin, 2008).
Nitric oxide also acts as a vasodilator. A vasodilator widens and opens the blood vessels, helps supply the body with oxygen and other nutrients, and lowers blood pressure. Nitric Oxide also supports the immune defense by inhibiting pathogens (Lundberg & Weitzberg, 1999).
On the flip side, Mouth breathing bypasses this mechanism, reducing oxygen efficiency and potentially increasing stress levels (Lundberg & Weitzberg, 1999)

3. Filtration, Humidification, and Temperature Regulation

The nose filters, warms, and humidifies incoming air, optimizing it for gas exchange in the lungs (Elad, Wolf, & Keck, 2008). Warming of the air allows the sensitive alveoli to response to the gas exchange.
This process also reduces irritation and infection risk, while mouth breathing delivers colder, drier, unfiltered air, which can stress the respiratory system (Elad et al., 2008).

4. Improves Heart Rate Variability (HRV) and Emotional Regulation

Slow, rhythmic nasal breathing (about 5–6 breaths per minute) increases HRV, an indicator of healthy parasympathetic tone (Lehrer, Vaschillo, & Vaschillo, 2000).
- HRV is the time between heart beats. A higher HRV (usually associated with younger people) means your nervous system is resilient and able to cope with stress. When the HRV is lower it indicates a 'stressed out' PNS, and usually comes with anxiety, sleep issues and other health issues.
This also synchronizes cardiac and respiratory rhythms, enhancing calmness and emotional regulation (Russo, Santarelli, & O’Rourke, 2017).

Summary

Bottom line: When we breathe slowly through our nose, we regulate our nervous system. It reduces and regulates the stress response and helps calm the body and brain.

Process	Physiological Mechanism	Effect	Key References
Nasal breathing	Activates vagus nerve; releases nitric oxide (NO)	Promotes relaxation & improves oxygenation	Gerritsen & Band (2018); Lundberg et al. (2008)
Slow exhalation	Increases parasympathetic tone	Lowers heart rate & blood pressure	Lehrer et al. (2000)
Mouth breathing	Bypasses nasal filtration & NO production	Can heighten stress or fatigue	Elad et al. (2008)

References

Elad, D., Wolf, M., & Keck, T. (2008). Air-conditioning in the human nasal cavity. Respiration Physiology & Neurobiology, 163(1–3), 121–127. https://doi.org/10.1016/j.resp.2008.06.017

Gerritsen, R. J. S., & Band, G. P. H. (2018). Breath of life: The respiratory vagal stimulation model of contemplative activity. Frontiers in Human Neuroscience, 12, 397. https://doi.org/10.3389/fnhum.2018.00397

Guyton, A. C., & Hall, J. E. (2021). Textbook of Medical Physiology (14th ed.). Elsevier.

Lehrer, P. M., Vaschillo, E., & Vaschillo, B. (2000). Resonant frequency biofeedback training to increase cardiac variability: Rationale and manual for training. Applied Psychophysiology and Biofeedback, 25(3), 177–191. https://doi.org/10.1023/A:1009554825745

Levitzky, M. G. (2013). Pulmonary Physiology (8th ed.). McGraw-Hill Education.

Lundberg, J. O., & Weitzberg, E. (1999). Nasal nitric oxide in man. Thorax, 54(10), 947–952. https://doi.org/10.1136/thx.54.10.947

Lundberg, J. O., Weitzberg, E., & Gladwin, M. T. (2008). The nitrate–nitrite–nitric oxide pathway in physiology and therapeutics. Nature Reviews Drug Discovery, 7(2), 156–167. https://doi.org/10.1038/nrd2466

Porges, S. W. (2011). The Polyvagal Theory: Neurophysiological Foundations of Emotions, Attachment, Communication, and Self-Regulation. W. W. Norton & Company.

Russo, M. A., Santarelli, D. M., & O’Rourke, D. (2017). The physiological effects of slow breathing in the healthy human. Breathe, 13(4), 298–309. https://doi.org/10.1183/20734735.009817

West, J. B. (2012). Respiratory Physiology: The Essentials (9th ed.). Lippincott Williams & Wilkins.

Putnam RW, Filosa JA, Ritucci NA. (2004). Cellular mechanisms involved in CO(2) and acid signaling in chemosensitive neurons. American Journal Physiology; Cell Physiology. 287(6), 1493-1526. doi.org/10.1152/ajpcell.00282.2004.