Jerath R, Crawford MW, Barnes VA, Harden K. Self-regulation of breathing as a primary treatment for anxiety. Appl Psychophysiol Biofeedback. 2015;40(2):107-115. doi:10.1007/s10484-015-9279-8
One-Sentence Summary:
Slow, deep breathing reduces the excitability of cells in the heart and brain, explaining physiologically how it reduces stress and anxiety.