Science 411
Nicholas Heath
Effect of breathwork on stress and mental ...

To date, this is probably the most significant study ever published on breathing.

Science 411
Nicholas Heath
Influence of a 30-Day Slow-Paced Breathing ...

Fifteen minutes of slow breathing (6 breaths per minute) before bed for 30 days improves sleep quality and increases vagal tone.

Science 411
Nicholas Heath
Heart rate variability biofeedback in chronic ...

HRVB (and, hence, slow breathing) is a powerful adjunctive therapy for managing a wide variety of chronic diseases. To be effective, it should be practiced for a minimum of 10 min/day (but probably 20+ for best results—see next section). More broadly, this study supports using slow breathing at around 5-6 breaths per minute in people with chronic diseases.

Science 411
Nicholas Heath
Deep Breathing Practice Facilitates Retention ...

We can use slow alternate nostril breathing immediately after learning a skill to improve that skill's short and long-term retention. More broadly and simply stated, this study supports using ANB after a task for enhanced learning.

hypertension

Effects of diaphragmatic deep breathing exercises on prehypertensive or hypertensive adults: A literature review

Slow breathing between 6 to <10 breaths a minute, with or without a device, for at least 10 minutes a day for 4+ weeks significantly reduces blood pressure, improves blood flow to vital organs, and improves autonomic dysfunction in people with hypertension or prehypertension.

Device and non-device-guided slow breathing to reduce blood pressure: A systematic review and meta-analysis (2019)

Slow breathing reduces systolic blood pressure by 5.62 mmHg and diastolic blood pressure by 2.67 mmHg. The more time you practice per week, the greater the blood pressure reductions. This is a go-to reference for anything slow breathing and hypertension-related.