You might be surprised to learn that mouth breathing is very detrimental to many aspects of your life. About 50% of our population are mouth breathers, a rate that is directly tied to the 40% of us who suffer from chronic nasal obstruction (Nestor, 2020). Nasal cavity congestion contributes to decreased airflow, which can increase bacteria growth. This can lead to infections, colds, allergies and more congestion, which ultimately lends itself to more mouth breathing. Breathing only through our mouth increases blood pressure and decreases heart rate variability (a measure of nervous system balance). In addition, when we mouth breathe, heart rate will increase, mental acuity will decrease, and body temperature will decrease. All of these related factors put the body in a state of stress, and fatigue.

Mouth breathing decreases pressure and causes the tissues in the back of the throat to flex inward and loosen. This decreases space in the mouth and alters the placement of teeth. With this increased challenge to our breathing, when we sleep and mouth breathe, our airways collapse even more, which contributes to snoring and sleep apnea. Mouth breathing also considerably increases water loss, which strangely enough, causes an increase in urination. The pituitary gland releases hormones during deep and restful sleep that communicate to our cells to store water; this allows us to sleep through the night without the need to urinate or quench our thirst. If we’re not able to sleep deeply (for many reasons, but including sleep apnea), the pituitary hormones aren’t released, and we become thirsty and have to use the bathroom in the middle of the night.

When we mouth breathe the depth and rate of our breathing increases. This creates hyperventilation and/or over-breathing, i.e., breathing in excess of the body’s metabolic requirements (Gardner, 2003). This hyperventilation leads to an increase of carbon dioxide elimination when we exhale. Our bodies produce carbon dioxide as a byproduct of cellular respiration, or the process of metabolizing carbs, fats, and proteins into energy (Khurana, 2012). When we have a reduction in carbon dioxide in the lungs and blood (hypocapnia), pH levels rise causing respiratory alkalosis, and blood flow to the brain decreases by up to 2% (Pizzorno et al., 2016). This can lead to neurological symptoms such as paresthesias in the extremities, dizziness, headache, and impaired concentration and memory (Evans, 2005).

If we have more oxygen than carbon dioxide in the blood and lungs, this might sound like a good thing, but not necessarily. Hemoglobin, a protein in the blood that gives it that red color, carries oxygen from the lungs to the tissues of the body and then it picks up carbon dioxide, and delivers it to the lungs to be exhaled out. The only way the oxygen is released from the hemoglobin is if there is carbon dioxide to exchange. If we have less carbon dioxide in the body (secondary to over-breathing or hyperventilation), then less oxygen is going to be provided for the cells and tissues of the body. All of that extra oxygen that was inhaled is going to waste because it can’t be used by the body.

You might wonder how all of this plays out when you are exercising. An early study of professional cyclists found that when participants were only allowed to breathe through their mouth, they didn’t fare well in their breathing rate or ability to tolerate increasing intensity (Douillard et al. 1995). In contrast, when only allowed to breathe through their nose, the cyclists were able to cut their exertion in half and increase their endurance. Adequate oxygen was able to get to the working tissues because they were breathing within their metabolic requirements. This allowed the tissues to go through aerobic respiration and fuel the metabolism to produce energy.

So, if you’re looking to improve cardiovascular health, and your overall health on top of that, start with some simple nasal breathing, all the time. When you are exercising, no matter whether it’s strength training, Pilates, running, cycling, HIIT class, etc. try to breathe strictly through your nose. This is going to be challenging, and it can be anxiety provoking, especially when you are new to it, and if you have to mouth breathe go for it, but then go back to nasal breathing as quickly as possible. It will feel like you’re not getting enough oxygen into the body, but you are getting more than enough. Your body is used to over-breathing and it will take time to adjust, but the overall benefits are worth it.