The vagus nerve and breathing: what slow breathing does

What is the vagus nerve?

The vagus nerve is the longest of the nerves that come straight from the brain. Its name means wandering, and it wanders a long way: from the brainstem, down the neck and into the chest and abdomen, with branches to the throat, heart, lungs and gut. Most of its fibres carry information up to the brain about how the body’s organs are doing; the rest carry signals down.

It is the main nerve of the parasympathetic nervous system, the “rest and digest” side of your automatic nervous system, which works in balance with the “fight or flight” sympathetic side. One of its jobs is acting as a brake on your heart: the more active it is, the slower your heart beats.

How breathing affects it

Every breath changes the vagus nerve’s grip on your heart. As you breathe in, the brake eases a little and your heart speeds up. As you breathe out, the brake comes back on and your heart slows. This rise and fall is normal and healthy, and it is what heart rate variability largely measures.

Two things make the swings bigger. One is breathing slowly, at around six breaths a minute, where the breathing rhythm lines up with the reflex that controls blood pressure. The other is a longer out-breath, which gives the brake more time. That combination is the basis of resonance breathing, cyclic sighing and most other calming exercises.

What the research shows

The short-term effect is well established. A 2022 review of 223 studies found that slow breathing raises the vagal measures of heart rate variability during practice and afterwards. Researchers have proposed that this respiratory stimulation of the vagus nerve may explain much of the calming effect of meditation, yoga and breathing practices, though that is a theory still being tested.

What is less clear is how much of the benefit of breathing exercises comes through the vagus nerve and how much through other routes, such as attention, distraction and a sense of control. Vagal activity can’t be measured directly in people, only estimated from heart rate variability.

Claims to be wary of

Online, the vagus nerve has become a catch-all explanation, with promises of “resetting” it to cure anxiety, gut problems, inflammation or fatigue. Some of these claims borrow from real research on medical vagus nerve stimulation, which uses implanted or external devices and is used for some people with epilepsy or depression. Breathing exercises are not the same thing, and there is no good evidence that they reset anything. They can help you feel calmer, which is worthwhile in itself.