Most of us learned that breathing is simple: oxygen goes in, carbon dioxide goes out. But there’s actually a third gas that quietly determines how well you sleep, how calm you feel, and how efficiently your body uses oxygen—nitric oxide.
Understanding this three-gas system is especially important right now, because winter creates a perfect storm for poor sleep that doesn’t exist in any other season. While we’re focused on staying warm and cozy, we’re unknowingly sabotaging the very air we breathe all night long.
Why Winter Wrecks Your Sleep
During summer, we worry about pollen and wildfire smoke here in California. But winter is when the real air quality problems happen—right inside your home.
We seal our windows to keep the heat in. We close our doors to save energy. And while we’re sleeping soundly (or trying to), something invisible is building up in our bedrooms: carbon dioxide.
Two adults sleeping in a closed bedroom for 7-8 hours can easily push CO₂ levels to 1,500-2,500 parts per million. Outdoor air sits at around 420 ppm. That’s a massive difference, and your body absolutely notices.
Elevated CO₂ isn’t poisonous, but it changes how your brain and nervous system behave.
When CO₂ rises while you sleep, your brain senses “air hunger.” Your fight-or-flight system kicks in. Your breathing becomes faster and shallower. Your sleep fragments. Your heart rate variability drops. Your deep sleep is directly affected—which means your sleep scores will show it. You wake up feeling unrested, irritable, or anxious—and you have no idea why.
This is why winter often brings:
- Increased irritability and anxiety
- Depressed or low mood
- Poor concentration
- Weakened immune function
- Higher susceptibility to colds and flu
Oh, and get this: air filters don’t help with CO₂!
You can have the best HEPA filter money can buy, perfect humidity levels, and pristine particle counts—but filters do absolutely nothing to remove carbon dioxide.
Only fresh air exchange does that.
The Mouth Breathing Problem
When you breathe through your mouth (especially during sleep), you tend to over-breathe. You’re moving more air per minute than your body actually needs at rest.
This causes you to blow off too much CO₂ from your blood, which makes breathing less efficient and shifts your nervous system toward alertness—exactly what you don’t want when you’re trying to sleep.
Natural nose breathing is perfectly designed to prevent this over-breathing of CO₂. The problem is, you can’t control what happens when you’re asleep. How do you know your mouth isn’t falling open at night unless you’re awake and aware—which, hopefully, is not the case? This is exactly why mouth taping can be such a game-changer.
When you breathe through your nose instead of your mouth:
- Your ventilation becomes slower and more efficient
- CO₂ stays at healthier levels in your blood
- The urge to “pant” decreases
- Sleep becomes more stable
- Deep sleep improves—and your sleep tracker will prove it
- Your respiratory rate drops—another metric your tracker will show
- Your heart rate variability (HRV) increases—a key marker of recovery and nervous system health
Mouth taping ensures you maintain nasal breathing all night long, even during deep sleep when you have no conscious control over your jaw. And yes, this also means you’re expelling slightly less CO₂ into your bedroom air overnight—a small bonus for both you and your sleeping partner.
The Third Gas: Nitric Oxide
This is the gas most people have never heard of, but it’s absolutely critical for good health.
Your body produces nitric oxide in two main ways:
- Inside your nasal passages when you breathe through your nose
- By beneficial bacteria in your mouth that convert dietary nitrates into nitric oxide
Why does this matter? Nitric oxide:
- Dilates your airways and blood vessels
- Improves oxygen delivery to your tissues
- Enhances how efficiently your lungs work
- Supports calmer, more rhythmic breathing patterns
After about age 40, your body’s natural nitric oxide production drops sharply. But the good news is that the bacteria in your mouth can keep producing it indefinitely—if you don’t kill them off.
This means you should:
- Avoid antiseptic mouthwashes that sterilize your mouth
- Avoid harsh toothpastes that wipe out beneficial bacteria
- Support your oral microbiome instead of trying to disinfect it (this is one reason why I oil pull with an MCT blend, instead of using mouthwash)
What to Eat for Better Breathing
Winter is the perfect time to be intentional about supporting nitric oxide production through your diet. Focus on nitrate-rich vegetables like:
- Arugula
- Beets
- Spinach
- Lettuce
You might also consider an NO lozenge like this one before bed to support healthy dilation overnight. When you combine nasal breathing with good nitric oxide levels, your body can use oxygen more efficiently with less breathing effort.
This creates a virtuous cycle: better oxygen delivery + balanced CO₂ + healthy NO signaling = deeper, more restorative sleep.
The Simplest Sleep Upgrade This Winter
You don’t need expensive equipment or complicated protocols. Just do this:
- Crack a window at night—even just a little bit makes a huge difference
- Use warm blankets or clothing instead of sealing the room tight
- Consider a CO₂ meter to see what’s really happening in your bedroom overnight (aim to keep levels below 1,000 ppm)
- Prioritize nasal breathing (mouth taping can help if you’re a mouth breather)
- Support nitric oxide production through diet and oral microbiome care
Fresh air isn’t a luxury. It’s a biological requirement.
During the darkest, coldest months of the year, your bedroom CO₂ level may be the single most overlooked factor affecting your sleep quality, mood, and immune health.
Open the window. Breathe through your nose. Let the three gases do what they’re designed to do.
-Mark
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