In the Bible breath is referred to as, "the breath of life." In yogic tradition the breath is acknowledged as an effective way to create more prana, or life force. In these and also in other traditions we see that the breath has long been recognized as a force to bring life and vitality.
The science behind the deep breathing in yoga is based on the healing and vitalizing power of oxygen. The breath combined with the poses, or alone in seated pranayama, replaces toxic stagnant energy with vital, freshly purified and oxygenated blood. The deeper you breath, the more energy you create, that will be distributed through out your body for healing. Our bodies are miraculous creations. When we supply them with what they need, healing happens. So slow down and take some nice deep breaths!