Breath, brain & balance: the science behind breathing and nervous system regulation

We often think of breath as passive and automatic - something our body just does behind the scenes. Yet breath is also the most immediate and accessible way we can tune into our nervous system. Ancient traditions from yoga, meditation, and contemplative practices have long held that how we breathe shapes our state of mind and regulation. Today, neuroscience provides compelling evidence that these traditions had insight: the breath is both messenger and medicine.

In this post, I’ll show how stress and breathing intertwine at the level of brain circuits and autonomic physiology, explore how certain everyday patterns disrupt that harmony, and then offer embodied practices - grounded both in science and wisdom - for restoring balance.

How breathing works: the basics of gas exchange & balance

Before we get into how the brain and nervous system shape the breath, it helps to understand what’s actually happening every time we inhale and exhale - because much of what people believe about “good breathing” is backwards.

When we breathe in, oxygen (O₂) enters the lungs and moves into the bloodstream, where it’s carried to the body’s cells for energy.

As those cells use oxygen, they produce carbon dioxide (CO₂) - a waste gas that we exhale.

Most people think CO₂ is something to get rid of as quickly as possible. But that’s not the full story. CO₂ is actually the main driver of your breathing rhythm, a key part of nervous system balance and important for optimising our cells for physical performance (like yoga asanas!).

CO₂ is your breathing signal

When CO₂ levels rise, sensors in your body - called chemoreceptors - send a message to the brainstem (the lower part of your brain that controls automatic functions like breathing and heart rate).

The brain interprets this as a cue to inhale, allowing you to breathe out the excess CO₂ and bring in more oxygen.

Then, as you exhale, CO₂ levels fall slightly again. This gentle rise and fall keeps your breathing pattern steady and your internal environment balanced.

Over-breathing upsets this balance

When we breathe too much - for example, taking large or rapid breaths, sighing frequently, or constantly talking - we blow off too much CO₂.

Low CO₂ (known as hypocapnia) can:

• Narrow blood vessels in the brain and body, reducing oxygen delivery.

• Make you feel dizzy, anxious, tired, or light-headed.

• Cause the brain to become less sensitive to natural CO₂ changes over time, disrupting the normal rhythm.

So paradoxically, breathing too much oxygen can actually make the body feel more stressed.

The goal is balance, not big breaths

Healthy breathing isn’t about taking deep or dramatic breaths - it’s about allowing CO₂ and O₂ to stay in balance.That balance:

• Keeps your blood chemistry steady.

• Supports calm nervous system activity.

• Allows the body to move between effort and rest with ease.

Every technique that helps to “regulate the nervous system” through breath - from pranayama to slow nasal breathing - ultimately works by re-balancing CO₂ and oxygen, restoring the natural rhythm that keeps us calm and clear.

How breath and the nervous system work together

Now that we understand how oxygen and carbon dioxide work together, let’s look at how that rhythm connects directly to the nervous system.

Deep in the brainstem (the lower, oldest, automatic part of the brain) sits a tiny group of nerve cells called the pre-Bötzinger complex. Think of it as your internal metronome for breathing - it keeps your breath going without you having to think about it.

The rhythm of our breath naturally shifts based on signals from chemoreceptors (tiny sensors that monitor CO₂ and acidity in your blood and the fluid around your brain, called cerebrospinal fluid).
When CO₂ rises, these sensors tell the brain it’s time to breathe in. When it falls, the system rests until the next inhale.

This rise-and-fall creates the steady rhythm that keeps you alive and also acts as a direct line to your autonomic nervous system - the part of your body that automatically regulates heart rate, digestion, and stress hormones.

The stress loop: when the brain and breath feed each other

When you’re stressed, areas of the brain like the amygdala (the emotional alarm centre) and the hypothalamus (which manages stress hormones) become more active.

These same regions also influence how you breathe - which is why stress often makes the breath faster and shallower.

That shift lowers CO₂, and low CO₂ keeps the body in a state of alertness - a self-reinforcing loop of tension. 

So the more anxious or busy you feel, the more you breathe; the more you breathe, the more anxious your body becomes. An unhelpful cycle when we’re faced with a full inbox, rather than a tiger! 

Learning to slow and steady the breath breaks that loop. It raises CO₂ just enough to tell your brain and blood vessels that you’re safe, restoring calm.

Research shows that breathing at a slower rhythm (around six breaths per minute) boosts heart-rate variability (HRV) - a marker of healthy vagus-nerve tone and resilience to stress.

Studies also show that gentle, steady breathing reduces activity in the amygdala and improves emotional control.

Diaphragmatic breathing: why slow and wide is better than a “big belly breath'“

One of the reasons slow, diaphragmatic breathing feels so instantly calming is its relationship with the vagus nerve - the body’s main relaxation pathway. The vagus nerve travels from the brainstem down through the chest and diaphragm, connecting to the heart, lungs and digestive organs. When we breathe deeply into the diaphragm, this movement gently massages and stimulates the vagus nerve, sending messages of safety back to the brain. In response, the body shifts toward the parasympathetic state — heart rate slows, digestion improves, and the whole system softens.

It’s worth noting that the common yoga cue of “belly breathing” is often well-intentioned but can be misleading. When people try to push the belly out forcefully, it can actually encourage over-breathing - taking in more air than the body needs and lowering carbon dioxide too much. Instead, think of slow, wide breathing: the breath expands through the ribs and side body as well as the abdomen, creating a steady, wave-like movement rather than a big belly push. This slower, gentler pattern supports balanced gas exchange and deeper nervous system regulation - the kind of breath that truly tells your body it’s safe.

Why nasal breathing helps regulate the system

Breathing through the nose rather than the mouth adds another layer of support for your brain and body.

Nitric oxide - the body’s built-in booster gas

Your nasal passages naturally produce a gas called nitric oxide (NO). It widens blood vessels, improves oxygen uptake in the lungs, and even has mild antimicrobial effects. When you breathe through your nose, you draw this nitric oxide down into your lungs, improving oxygen efficiency. When you breathe through your mouth, you miss out on this benefit completely.

Hydration, temperature and filtration

• The nose warms, filters and humidifies incoming air, protecting the delicate tissues of the lungs.

• Mouth breathing skips that process, drying the throat and mouth, increasing water loss, and letting in more dust, allergens and pathogens.

• Over time, habitual mouth breathing can contribute to poor sleep, dental issues and even structural changes in the jaw.

For most situations, nose breathing keeps the body calmer, better hydrated and more energised. Save mouth breathing for when your nose is blocked or during high-intensity effort.

Everyday disruptions to the breath–brain balance

Speech and subtle over-breathing

If you teach, talk for a living or spend hours on calls, you may unintentionally over-breathe. Speaking more than you rest means you exhale more than you inhale, which gradually reduces CO₂. That’s one reason long teaching or meeting days can leave you depleted or tense, even if you’ve been doing gentle work.

Frequent sighing (and a little yoga-class humour)

A sigh is the body’s way of resetting its breathing rhythm - it’s built into your brainstem’s automatic patterns. But if you’re sighing every few breaths, your system might already be working too hard to stay balanced.

One sigh can be therapeutic; twenty in an hour might just be over-ventilating with extra flair. Instead, aim for quieter, slower breaths that stabilise CO₂ rather than blow it away.

There are definitely some yoga teachers and classes out there that encourage lots of sighing. This is where you can take them up on the invitation to make this ‘your practice’ by skipping any excessive sighs!

Modern science catches up with ancient wisdom

Long before neuroscience began mapping the vagus nerve or measuring heart-rate variability, yogic and Eastern medical systems described the same physiological truths through energetic language. I still remember reading Prana and Pranayama by Swami Niranjanananda Saraswati for the first time and being struck by how clearly the ancient yogic texts described what we now recognise as the nervous system. Their language was different - they spoke of prāṇa, the intelligent life force that moves through us - but the understanding was the same. Even without modern measurements or technology, the yogis intuitively grasped how the rhythm of the breath governs the rhythm of the mind. Today, science calls this vagal tone, homeostasis, and autonomic balance; yoga simply calls it harmony. However we name it, the insight endures: when we breathe with awareness, we have the power to bring our body and mind back into balance - one conscious exhale at a time.

An embodied practice for everyday balance

Here’s a simple practice you can do anywhere to bring these ideas into your body.

1. Settle

Sit comfortably. Let your shoulders drop and jaw soften. Breathe normally for a moment.

2. Close the mouth, breathe through the nose

Feel the air travel quietly in and out. Allow the exhale to finish naturally, then rest briefly in the pause before the next inhale.

3. Notice sensations

Feel the temperature of the air, the movement in your ribs or belly, and the stillness between breaths. This moment of quiet is when your nervous system recalibrates.

4. Gently lengthen the exhale

If it feels easy, make your out-breath one second longer. Longer exhalations gently engage the vagus nerve (the body’s relaxation switch).

5. Return and reflect

Let your breath return to normal. Notice any shift in energy, clarity or mood. You can repeat this for two or three minutes between meetings, before sleep, or after stressful moments - tiny pauses that accumulate real change.

Integrate it into your day

• Take 30 seconds of slow nasal breathing before moving between tasks.

• Notice sighs or breath-holding as feedback, not faults.

• When you speak for long periods, pause periodically to breathe quietly through your nose.

• Practise consistency rather than intensity - a few minutes, a few times a day, will reset your baseline faster than one long session.

Final thoughts

Your breath is the simplest and most faithful mirror of how you’re doing. It’s also a tool you have at your disposal all of the time, wherever you are.  By learning its patterns - and gently reshaping them - you can influence your chemistry, your stress response, and your sense of ease. Ancient teachers called this prāṇa or Qi; neuroscience calls it self-regulation. Either way, the insight is the same: your breath is your body’s built-in way home.

Research round up for the curious (and the nerdy 🤓)

If, like me, you love diving into the details, here are a few of the studies and reviews that inspired this article. Each one looks at a different aspect of how breath, the brain, and the nervous system communicate.

• How slow breathing affects the body’s automatic systems
  An overview of the physiological effects of slow breathing in healthy humans - a clear overview of how slow, steady breathing enhances heart-rate variability (HRV) and balances the autonomic nervous system.

• The science behind calm: why controlled breath changes emotion
  A systematic review that summarises dozens of studies showing that slow breathing increases parasympathetic activity, steadies the mind, and improves emotional regulation. Basically, how breath control can change your life!

• What happens in the brain when we focus on breathing
  An explanation of how mindful attention to breath regulates emotions via increased amygdala–prefrontal connectivity. An Imaging study showing that focusing on the breath reduces activity in the brain’s fear centre (amygdala) and strengthens its connection to regions involved in control and calm.

• Nasal vs mouth breathing: a measurable difference
  A fairly technical overview of why acute nasal breathing lowers diastolic blood pressure and increases parasympathetic contributions to HRV, demonstrating that nasal breathing triggers a stronger relaxation response and lowers blood pressure compared to mouth breathing.

• Nitric oxide - the hidden benefit of nasal breathing
  A study that looked at humming, showing how nasal breathing (and humming) naturally boosts nitric oxide production, improving oxygen delivery and antimicrobial defence.

• How slow breathing improves heart and emotional regulation
  Researchers found that breathing more slowly can steady the heart, reduce negative emotions, and increase feelings of calm and wellbeing.

• Breath and mood: beyond mindfulness
  This research showed that short, structured breathing practices can lift mood and reduce stress more effectively than mindfulness meditation alone.

• Pain, perception, and the breath
  This study found that slow, deep breathing can reduce pain sensitivity and calm the body’s stress response by lowering sympathetic (fight-or-flight) activity.