Slow breathing: what the research says, and how to do it

Slow down your breathing and, within a minute, your heart rhythm changes. It is one of the few parts of your nervous system you can steer on purpose.

It is also surrounded by bold claims online. In earlier articles we looked at the vagus nerve and vagal tone. Here, as a gastroenterologist, I focus on the breathing itself: what it does in the body, which techniques have evidence, and how to try it.

What counts as slow breathing

At rest, most adults breathe 12 to 20 times a minute without thinking about it. Researchers usually define slow breathing as fewer than 10 breaths a minute [1, 2]. Many studies use about six breaths a minute: roughly five seconds in and five seconds out.

What happens in your body

Your heart rate naturally rises a little as you breathe in and falls as you breathe out. This rhythm is called respiratory sinus arrhythmia, and the slowing on the out-breath is driven by the vagus nerve [2].

When you breathe slowly, those swings become larger. At around six breaths a minute, the breathing rhythm lines up with the body's blood pressure control system (the baroreflex), and the heart rate swings are at their biggest. Researchers call this "resonance" breathing [3].

Slow breathing also tends to:

• make each breath deeper and use the diaphragm more [2]
• increase measures of vagus nerve activity, such as heart rate variability (HRV), during and shortly after practice [4]
• shift the body towards its "rest and digest" state [1]

Slow breathing is one of the few direct, voluntary ways to engage the vagus nerve, and it costs nothing.

One caveat matters. Because the breathing pattern itself enlarges the heart rhythm's swings, a higher HRV reading during practice does not prove that your resting vagal tone has changed [3, 4].

What the research shows

In the moment. A 2022 meta-analysis of studies in healthy people found that voluntary slow breathing increased vagally mediated HRV during the practice, immediately afterwards and after repeated sessions [4]. An earlier systematic review found similar changes, together with people reporting feeling more relaxed and less anxious [1].

For stress and mood. A 2023 meta-analysis of 12 randomised controlled trials found that breathwork was linked to lower self-reported stress, with a small to medium effect [5]. In a one-month randomised study, five minutes a day of "cyclic sighing" (a breathing pattern with a long out-breath) improved mood and lowered resting breathing rate more than mindfulness meditation did [6].

The limits. Most studies are small, use self-reported outcomes and cannot hide from participants which group they are in. The authors of the 2023 meta-analysis rated most trials as having some risk of bias [5]. The effects are real but modest. Slow breathing is a useful tool, not a cure-all.

Popular techniques, and the evidence behind them

• Resonance breathing (about six breaths a minute). In for about five seconds, out for about five seconds. The best-studied pace, and the one used in HRV biofeedback [3].
• Longer out-breath (for example, in for four, out for six). Puts extra emphasis on the out-breath, when the vagus nerve slows the heart. Widely recommended; shares the evidence for slow breathing generally [1, 4].
• Cyclic sighing. Two breaths in through the nose (a full breath, then a short top-up), followed by a long, slow breath out. Supported by one well-designed randomised study [6].
• Box breathing (in four, hold four, out four, hold four). Popular in the military and sport. Slows the breath, but has little research of its own.
• 4-7-8 breathing (in four, hold seven, out eight). Also slows the breath. We found no good-quality trials testing it specifically.

The common thread is a slower pace and an unhurried out-breath. The exact count matters less than slowing down comfortably.

How to try it

1. Sit comfortably with your back supported, or lie down.
2. Breathe in gently through your nose for about four to five seconds, letting your tummy rise.
3. Breathe out slowly for about five to six seconds, through your nose or through softly pursed lips.
4. Keep it comfortable. The breath should feel easy, not forced or extra-deep.
5. Start with five minutes, once or twice a day. A timer or a free breathing app can help you keep the pace.

Many people find it useful before a stressful event, at bedtime, or before a meal. Our article on how stress affects your digestion explains why calming the nervous system before eating can help your gut.

Who should be careful

Slow breathing is safe for most people. Stop and breathe normally if you feel dizzy, light-headed, tingly or short of breath. These are signs of breathing too deeply rather than too slowly.

If you have a heart or lung condition, or are unsure whether breathing exercises are right for you, speak to your GP before starting a regular practice. Breathing exercises are not a substitute for medical assessment of symptoms such as chest pain or breathlessness.

The bottom line

Slow breathing, at around six breaths a minute with a longer out-breath, reliably shifts heart rhythm and vagus nerve activity within minutes. Over weeks, regular practice is linked to modest reductions in stress. It is free, simple and low-risk, and the best technique is the one you will actually use.

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Frequently asked questions

How many breaths a minute is slow breathing? Researchers usually define slow breathing as fewer than 10 breaths a minute [1]. Many studies use about six breaths a minute, for example breathing in for five seconds and out for five seconds. A typical adult at rest breathes 12 to 20 times a minute.

How long does slow breathing take to work? Changes in heart rhythm appear within a minute or two [4]. Studies of stress and mood usually use five to 20 minutes a day, practised for several weeks [5, 6].

Is box breathing or 4-7-8 breathing better? Neither has been tested much in its own right. Both slow the breath, which is the part with evidence. A simple pace of about six breaths a minute, with a longer out-breath, is the best-studied option [3, 4].

Is slow breathing safe? For most people, yes. If you feel dizzy, tingly or short of breath, stop and breathe normally. If you have a heart or lung condition, check with your doctor before starting a regular practice.

Declaration of interest: The author is the founder of CortiAura, a company developing vagus nerve technology. This article is educational and makes no claims about any CortiAura product.

References

1. Zaccaro A, Piarulli A, Laurino M, et al. How breath-control can change your life: a systematic review on psycho-physiological correlates of slow breathing. Frontiers in Human Neuroscience 2018;12:353.
2. Russo MA, Santarelli DM, O'Rourke D. The physiological effects of slow breathing in the healthy human. Breathe 2017;13(4):298–309.
3. Lehrer PM, Gevirtz R. Heart rate variability biofeedback: how and why does it work? Frontiers in Psychology 2014;5:756.
4. Laborde S, Allen MS, Borges U, et al. Effects of voluntary slow breathing on heart rate and heart rate variability: a systematic review and a meta-analysis. Neuroscience & Biobehavioral Reviews 2022;138:104711.
5. Fincham GW, Strauss C, Montero-Marin J, Cavanagh K. Effect of breathwork on stress and mental health: a meta-analysis of randomised-controlled trials. Scientific Reports 2023;13:432.
6. Balban MY, Neri E, Kogon MM, et al. Brief structured respiration practices enhance mood and reduce physiological arousal. Cell Reports Medicine 2023;4(1):100895.

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