We are evolutionarily designed to nose breath. The nose is the start of the respiratory system. The mouth was evolutionarily designed to begin the digestion process, not the respiratory process. Mouth breathing is essentially an "emergency state" that we have come to live in.
Nose breathing releases nitric oxide in the body, which increases the CO2 levels in the blood. The level of CO2 in the blood then regulates the release of O2 into the cells to maintain the balance. Mouth breathing does not release nitric oxide, and thus, less oxygen gets released into the cells (leading to all sorts of symptoms such as fatigue, anxiety, depression, digestive issues, immune issues, etc.)
Mouth breathing, especially while asleep, plays a HUGE role in dental health. Tooth decay and cavities are a big sign of mouth breathing because when the mouth is dehydrated (ie: you wake up with a dry mouth), there is little saliva in the mouth. Saliva plays a key role in maintaining a healthy biome in the mouth. Saliva contains the essential minerals and enzymes needed for healthy teeth, as well as keeps a proper pH in the mouth to allow for beneficial bacteria. Again, this is the start of the digestive process, so mouth breathing can play a huge role in digestive problems down the line. The mouth is slightly acidic, to aid in digestion, so when the saliva disappears or the pH becomes to alkaline, the biome gets disrupted.
Because nose breathing is so much more efficient in the body's oxygen exchange, when you mouth breathe at night, your brain may not be getting the O2 it needs. This puts the brain in a distressed state, at the most important time, where it should be resting and recovering. Snoring, sleep apnea, teeth grinding, and anxiety are all signs of mouth breathing.
Nose breathing activates the parasympathetic nervous system when the tongue rests on the roof of the mouth, which aids in rest and recovery. If you're waking up feeling anxious, it could be because your brain didn't receive the oxygen it needs during night time because of mouth breathing, meaning that it stayed in a "flight or fight" mode all night.
Your digestive system also relies on your parasympathetic nervous system. If your body doesn't get any time in that state, digestive issues can arise.
Nose breathing helps develop sinus cavities and a wider face structure. This is important for developing children. If you notice your child is mouth breathing, speak to your doctor about it, and try the techniques below with them as well.
Tips to increasing your nose breathing:
Article: Could Nasal Breathing Improve Athletic Performance?
Podcast: The secret to better sleep. (26:07)
Podcast: The secret to better sleep: Stop doing this one thing. (1:43:37)
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