The Bohr Effect
Why CO₂ Isn't
a Waste Gas

The oxygen delivery problem

Oxygen is carried in the blood bound to haemoglobin, the protein in red blood cells. When haemoglobin picks up oxygen in the lungs, it holds it tightly. For that oxygen to be released into the tissues that need it — the brain, the muscles, the organs — haemoglobin needs a signal to let go. That signal is CO₂.

This is the Bohr effect, described by Danish physiologist Christian Bohr in 1904. When CO₂ levels in the blood are at their normal range, haemoglobin releases oxygen efficiently to the surrounding tissues. When CO₂ is low — as it is when someone is over-breathing — haemoglobin holds onto oxygen more tightly, and less of it reaches the cells that need it. You can have perfectly normal blood oxygen saturation and still be functionally oxygen-deficient at the cellular level if your CO₂ is too low.

Why this matters for anxiety and burnout

Chronic stress drives chronic overbreathing. Overbreathing lowers CO₂. Low CO₂ impairs oxygen delivery via the Bohr effect, and simultaneously causes blood vessels — including those supplying the brain — to constrict. The brain receives less blood and less oxygen. The result is a cluster of symptoms that are strikingly similar to the experience of anxiety and burnout: brain fog, difficulty concentrating, light-headedness, fatigue that sleep doesn't fully resolve, and a persistent sense of not functioning at full capacity.

Many people in this state breathe harder, trying to get more oxygen — which makes things worse, not better, because the problem is not insufficient oxygen in the lungs but insufficient CO₂ to deliver it to the tissues. Breathing more removes more CO₂ and tightens the cycle further.

CO₂ and nervous system reactivity

Low CO₂ also affects the nervous system directly. When CO₂ drops below its healthy range, blood pH rises — the blood becomes more alkaline. This alkalosis increases the excitability of nerve cells, making them more likely to fire spontaneously or in response to minor stimuli. The practical effects include heightened anxiety, a lower threshold for panic, pins and needles or numbness (particularly in the hands, feet, and around the mouth), and muscle tension or cramping.

These are not psychological symptoms with a physical component — they are physiological symptoms with psychological consequences. The nervous system is genuinely more reactive because its chemical environment has changed. Understanding this is important because it means that addressing the breathing pattern directly — rather than managing the anxiety symptoms it creates — is the more efficient intervention.

The BOLT score as a CO₂ measure

The Body Oxygen Level Test, or BOLT score, is a simple way to assess CO₂ tolerance. You take a normal breath out through the nose, then pinch the nose and time how long it takes before you feel the first distinct urge to breathe. This urge is triggered by rising CO₂, and the time it takes to arrive reflects how tolerant your body is of CO₂ at its normal resting level.

A BOLT score below 20 seconds is associated with dysfunctional breathing patterns and the symptoms described above. Above 40 seconds reflects a well-regulated system. The score improves reliably with functional breathing practice — typically by several seconds within the first two weeks — and the improvements in anxiety, energy, and sleep quality tend to track closely with it.

CO₂ is not a waste product. It is a regulator, a vasodilator, a signal, and the mechanism by which your body delivers oxygen where it is needed. Keeping it at its healthy level is one of the most important things your breathing can do.