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.

2017

Oxygen-induced impairment in arterial function is corrected by slow breathing in patients with type 1 diabetes (2017)

Slow breathing improves autonomic and arterial function while also acting as an antioxidant in people with diabetes.  The last line of their abstract summarizes it perfectly: “Slow breathing could be a simple beneficial intervention in diabetes.”