Why Deep breathing is essential for us

Deep breathing means - Adopting a habit of breathing deeply.
From your nostril not from your mouth. That's it !
Normally most people ( i.e. almost 95 % of all of us) who are leading a sedentary life style and working on jobs that requires 'using their heads' all day long, the outcome of a busy, complex and demanding life is somewhat like this:
No energy in the end of the day, mental sluggishness, dilapidated bodies, greater susceptibility to germ and infections, wear-and-tear of the entire body, more work for the heart, irregular blood pressure, tensions in body and nerves etc.
Remember this important fact:
“To function properly, our brain needs three times more oxygen than the rest of our organs; and unless this is provided it will try to appropriate its supply by drawing on the over-all allotment! ”

This explains why so many city people, working at sedentary jobs, doing mental work all day long, tend to become dilapidated and have greater susceptibility to germ and infections than persons who lead active outdoor lives. Sedentary individuals are permanently oxygen-starved. Yet this situation can be avoided at will.
Air is nourishment to our bodies just as much as food and drink. Air gives our blood the supply of oxygen it must have in order to feed itself so that it may, in turn, feed the tissues, nerves, glands and vital organs. Without it our skin, bones, teeth and hair could not remain in condition. Our digestion-the process of utilizing the food we eat-fails at once without a proper supply of oxygen to the blood. Even our thinking processes are slowed down without intake and exhalation of fresh air-which is the reason mental sluggishness overtakes us in an ill-ventilated room
In a single day we breath about 23,000 times. The average volumes of air taken in with a single breath is about 20 cubic inches, depending on a person's size, sex, posture, the nature of the surrounding atmosphere and one's physical and emotional state. However, with proper attention given to the breathing, this volume may be increased to 100 or even 130 cubic inches per breath.
Breathing is an activity which is indispensable for our existence. Nobody can live without breathing as the oxygen is the life blood of all organisms on earth.
However, most of us breath in a shallow manner. The inhalation and exhalation of air in and out of body occurs on a very superficial level in most of us. People just don’t care to inhale deeply since they don't find any compulsive urge to do so.
Though not breathing deeply does not harm us directly, it has its own long term negative effects on our body.
Let us understand what happens when we do not adopt correct breathing:

As the average person reaches middle age, lung tissues tend to grow less and less elastic. Years of improper breathing take their toll. The chest itself has a tendency to grow rigid The consequences is an accumulation of uric acid in the blood stream which often leads to those vague syndromes of pain and discomfort that doctors in general diagnose with a shrug as the miseries of aging, which they can cheerfully advise you to learn to live with since nothing can be done about them.
Backaches, headaches, stiffening muscles and joints, neuritis, rheumatism are some of the more common of these complaints. Excess fat is another, for as we begin to grow old and proper circulation is impeded by a sluggish diaphragm or hardening arteries, the red blood corpuscles become distributed unevenly and fat accumulates in spots instead of being burned up.

However, all of these complaints may be avoided, or at least considerably retarded, if only we learn to breath scientifically. Deep breathing (along with Deep Contraction) also has a direct salutary effect on Obesity, Since the cleansing, stimulating action of deep breathing improves metabolism and that, in turn, transforms deposits of fat into body fuel, or added energy.
In other words,
"Careful reorientation of your breathing habits can provide you with 5 times the oxygen and rid you of five times the carbon dioxide, with which you habitually function."
Just incorporate a habit of deep breathing in your busy, complex and demanding life and all the above negative outcomes of it will vanish like a magic !