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You fall asleep with your mouth slightly open. That single habit lowers the oxygen reaching your brain all night.
You have fixed the room and the supplements. This is about the route the air takes. Your nose is the main source of the nitric oxide in the air you breathe in. Your mouth adds almost none.
When you breathe in through your nose, that nitric oxide travels down into your lungs with the air. It is a vasodilator. It opens the small vessels in your lungs and matches blood flow to the air sacs that are filling. More of the oxygen you breathe actually crosses into your blood.
Breathe through your mouth instead and you skip all of it. The same breath delivers less oxygen to your blood. The difference in a single breath is small. Repeated for eight hours, it is the clean oxygen supply your deep repair runs on.
The tell is simple. You wake with a dry mouth and a sore throat. That dry mouth means you breathed through it for hours. The foggy morning is what that route cost you.
Researchers who identified the nose as the body's main source of nitric oxide showed that breathing through it raises the oxygen level in your blood compared with breathing through your mouth. The gas made in your nose is what accounts for the difference.
That oxygenation finding is well documented. The direct proof that it improves a whole night of sleep is thinner, so treat the sleep gain as likely, not settled.
TONIGHT
In the last hour, breathe only through your nose, and keep breathing that way as you settle into bed. Lips together, jaw relaxed.
If your nose is blocked, clear it before bed so the nasal route is open. A saline rinse or a nasal strip that holds the nostrils open both work. You may have read about taping your mouth shut. Skip it if you snore heavily or have any breathing condition, and ask a doctor first if you are unsure.
The route your breath takes in the last hour is the oxygen your brain works with for eight hours. Keep your mouth closed, and let your nose do what it was built to do.
