Pranayama can make you sharp, improve vitality

Regular practice of Pranayama improves metabolism, resistance, functioning of sense organs and blood circulation. It purges impurities, purifies nadis, protects tissues and internal organs. It neutralizes lactic acid which causes fatigue.
Pranayama enhances circulation of bodily fluids within the stomach, kidneys, liver, spleen, intestines, skin and other organs. It improves the functioning of lungs which is key to good health. By enhancing the blood circulation to the lungs, Pranayama helps in preventing formation of toxins in the lungs.
Pranayama regulates liver functions. The liver regulates most chemical levels in the blood and produces bile. Bile helps break down fats, making them fit for absorption. The blood that passes through stomach and intestines reaches the liver where it is purified. It creates nutrients for the body to use. The liver supplies scavenger cells which collect, breakdown or store waste particles.
Pranayama, if it is done regularly and properly, can stimulate renal lymph flow, which is crucial for keeping the organ healthy. It helps in maintaining adequate blood flow to kidneys.
Doctors say about 80 per cent of the diseases is related to stomach. Many a time the food we consume is not digested properly. Pranayama triggers movement of abdominal muscles which stimulates the peristaltic and segmenting movements of the intestines and promoting intestinal circulation. Pranayama enhances blood circulation. This is very important for all bodily functions. Flow of pure blood tones the nerves, brain, spinal cord and cardiac muscles.
Regular practice of Paranyama helps improving concentration. It calms down the upsurge of the senses and desires. The number of thoughts thus generated in the mind gets reduced. Pranayama maintains firmness in the body and steadiness in the intellect. It is important for a spiritual practitioner to practice Pranayama daily. According to the Siva Samhita, practice alone brings strength and knowledge. Daily practice ensures success and perfect consciousness, which purge the sadhaka from the fear of death.
The Patanjali Yoga Sutra says as the rising sun slowly disperses the darkness of night, pranayama removes the impurities refines the sadhaka and prepares his body and mind to become fit for concentration (dharana) and mediation (dhyana).