The Mouth Breathing Problem Part I: The Loss of Oral Nitric Oxide

I’ve had someone tell me that it’s “complete rubbish” to say that nasal breathing is better for you than mouth breathing. Another person told me it was “bullshit”. A third told me it was the job of the lungs to move carbon dioxide out of the body and that the mouth is the best way to do it (only true during intense exercise—you actually need to keep some in the lungs).

Like so many discussions these days, people were adamant in their viewpoint and not interested in hearing why mouth breathing isn’t good for you. I’m okay with hearing alternative views and am open to changing my own as the science in this developing space evolves and grows.

However, the truth is, and there is plenty of science behind it, that mouth breathing isn’t good for our health, and for those who can, nasal breathing is the way to go. The one exception to this rule is during high-intensity exercise, when it isn’t possible to maintain nasal breathing. Over the next few posts, I will break down why mouth breathing is not the best option for your health, but today I will focus on oral nitric oxide (NO).

Like many parts of the body, the mouth has its own microbiome. In fact, your mouth is believed to contain more than 700 species of bacteria, fungi, viruses and protozoa (complex single-cell organisms). It’s the second most diverse microbiome in the human body, with the gut being the first. This microbiome is critical to your good health, aiding digestion, and is critical to the production of oral NO, which is a vasodilator and helps you to maintain good gut health. Unfortunately, if you breathe through the mouth, you can reduce or even eliminate the production of oral NO.

The production of oral NO follows an interesting process. When we eat nitrate-rich foods, like beetroot and spinach (or drink pomegranate juice), the nitrate is absorbed in the small intestine. From there, it enters your bloodstream, with around 25% of the nitrate you have absorbed being secreted back into the mouth in your saliva. In the mouth, your good oral bacteria convert the nitrate into nitrite. The final step in the production of oral NO occurs after you swallow, when your stomach acid converts some of the nitrite into NO or the nitrite travels further into the gut and is absorbed for systemic NO production.

The function of oral NO differs from NO produced in the nasal cavity. Your oral NO enters the digestive system rather than the lungs, supporting gut health, enhancing digestion, and acting as an antimicrobial agent. Specifically, it can reduce inflammation and improve blood flow to support healing and general health. A small amount enters the bloodstream from the gut, but the majority of NO in your blood is nasal NO.

If you mouth breathe, the constant flow of air dries out your mouth. This is exacerbated at night as your saliva production naturally drops when you are sleeping. This leads to two significant issues. First, less saliva means fewer nitrites entering the oral cavity, resulting in the production of less NO. Second, saliva contains bicarbonate ions, which neutralise acids. These can be acids in your food and drink (e.g. citrus) or acids produced by bacteria in your mouth that feed on the food you eat (especially sugar).

Without saliva, the environment of the mouth favours bacteria that produce acid and cause inflammation. If the acidity in the mouth becomes excessive, it can change the microbiome enough that the conversion of nitrate to nitrite is disrupted. If that happens, the volume of NO produced in the stomach is reduced or even eliminated. A loss of oral NO creates an imbalance in gut health and even systemic inflammation, which is related to some autoimmune diseases, poor cardiovascular health, and even neurodegeneration.

To preserve the production of oral NO and its benefits, it’s important to breathe through your nose. Whenever possible, you should only breathe through your mouth when you exercise to a level where nasal breathing is no longer sustainable. As my French teacher used to say when I was talking in class: Fermez la bouche! (Close your mouth!).

Disclaimer

This blog is for informational purposes only. It is not medical advice. Always consult a healthcare professional for personalized guidance and treatment.