There are three very essential prerequisites for vitality and rejuvenation: a healthy central nervous system
(brain and spine), healthy glands and healthy internal organs.
Healthy Central Nervous System (Brain and Spine)
Nerves from the brain and spine go to every tissue in the body and therefore the health of every tissue in the body depends upon the health of the brain and spine.
The headstand causes an increase in circulation to the brain, which stimulates the brain's nerve cells.
This results in increased vitality and improved brain function (intelligence and memory).
Since the nerves from the spine go to all the organs and glands of the body, a healthy spine obviously plays an important role in vitality and rejuvenation. In fact, the spine is more critical to our well-being than the brain, since the brain is well protected by the cranium or skull bone. Where the spinal nerves leave the spine and pass through the intervertebral foramina is a very vulnerable area. If a vertebra is slightly out of place, it may cause the nerve to be ‘pinched' in the intervertebral foramina. The spinal nerves do not have protection against mechanical insults as the brain does.
The ancient yogis fully understood the vulnerability of the spine and the tendency for slight spinal misalignments to occur. They also knew that if the spine was kept flexible by yoga asanas there would be much less chance of spinal misalignments. Some of the asanas will even correct some minor misalignments.
If you do nothing to improve your spine's flexibility as you get older, your spine will deteriorate further and the spinal nerves will be increasingly impinged upon. This will lead to further deterioration of your organs and glands, until eventually their actual structure becomes diseased. We call this organic disease. At this stage, not only is their function impaired, but their cells are actually dying. If the condition is too advanced, it is irreversible. It's at this stage that many people go to doctors and are told that they have, for example, cancer of some particular organ. The cancer has not appeared overnight; in reality it has been developing for many years.
Healthy Endocrine Glands
The most important are the pituitary, pineal, thyroid, adrenal, pancreas and sex glands. The pituitary and pineal glands are situated in the brain, the thyroid is in the neck area, the adrenals and pancreas in the solar plexus area and the sex glands in the pelvic region.
The function of these glands is to secrete powerful hormones which control your growth, weight and size.
They also determine your metabolism, vitality, sexual vigor and emotional state.
Since the pituitary and pineal glands are situated in the brain, the headstand has a powerful effect on them.
Thyroid gland problems are very common and often go undiagnosed until the symptoms are very obvious. The shoulder stand is specific for the thyroid gland and will prevent and help cure thyroid gland problems.
The hormones secreted by the sex glands are important not only for sexual virility but also for sparkling eyes, smooth skin and a warm personality. The reverse posture stimulates the sex glands and therefore the production of the sex hormones.

The adrenal glands produce a variety of hormones such as adrenaline and cortisone that are important in controlling your stress and immunity. The twist posture is a powerful stimulant to the adrenal glands, causing them to release extra energy to boost your vitality level.
The correct functioning of the pancreas is vital to our health. The pancreas, secretes two hormones, called insulin and glucogen, which help to balance the body's sugar level. If the pancreas is not working properly, diabetes may develop. Diabetes is a serious disease, since complications such as blindness, heart attacks or strokes may occur. To help prevent diabetes, it is recommended that you follow the nutritional principles outlined here, especially by avoiding concentrated sugar foods.
Healthy Internal Organs
As well as having a dramatic effect on the brain, spine and glands, most asanas also benefit the internal organs by massaging and stimulating them. These results in healthier internal organs that will function better and last longer.
As an example, the stomach lift raises the diaphragm, which massages the heart from below. This strengthens the heart muscle, resulting in better circulation and less chance of heart disease.
Healthy Digestive System
Even if we eat the most nourishing food, it still has to be digested and assimilated properly and the toxins have to be eliminated efficiently. As we get older the digestive system functions with gradually reducing efficiency. The asanas result in an improved blood and nerve supply to the digestive and eliminative systems, which in time will get them functioning at peak efficiency.
The stomach lift massages the digestive organs, as well as contracting and stretching them.
Healthy Joints
The stretching of the joints in asanas causes the secretion of a lubricant called synovial fluid. This is released into the joints and keeps them supple, as well as removing waste products. The result is to reduce stiffness, which will prevent arthritis or improve it if you already have the condition.
Healthy Skin
Stretching of the skin during the asanas causes stimulation of the skin cells. This results in firmer, healthier skin which won't sag or wrinkle