Vitamin A is an essential human nutrient. Vitamin A actually refers to a family of similarly shaped molecules: the retinoids. Its important part is the retinyl group, which can be found in several forms. In foods of animal origin, the major form of vitamin A is an ester, primarily retinyl palmitate, which is converted to an alcohol (retinol) in the small intestine. Vitamin A can also exist as an aldehyde (retinal), or as an acid (retinoic acid). Precursors to the vitamin (provitamins) are present in foods of plant origin as some of the members of the carotenoid family of compounds.

All forms of vitamin A have a Beta-ionone ring to which an isoprenoid chain is attached. This structure is essential for vitamin activity.  The orange pigment of carrot - Beta-carotene- can be represented as two connected retinyl groups. The retinyl group, when attached to a specific protein, is the only primary light absorber in visual perception, and the compound name is related to the retina of the eye.

Vitamin A can be found in various forms:

• Retinol, the form of vitamin A absorbed when eating animal food sources, is a yellow, fat-soluble, vitamin with importance in vision and bone growth. Since the alcohol form is unstable, the vitamin is usually produced and administered in a form of retinyl acetate or palatate.

• other retinoids, a class of chemical compounds that are related chemically to vitamin A, are used in medicine.

MINERALS

The body also requires special substances known as minerals. If minerals are lacking, the vitamins cannot perform their various functions; if vitamins are absent, however, the body can make some use of minerals.

As with vitamins, the body needs ever so little of each of the minerals, but minerals in their proper balance can make the difference between illness and glowing health.

The body needs at least sixteen minerals to maintain energy and lengthen life, and I believe that the minerals are very much more important to health than most people realize.

Minerals are able to maintain the water balance in your body which [is] required for life processes. They draw chemical substances in and out of your cells. Minerals help to keep blood and tissue fluid from becoming either too acid or too alkaline. Minerals also stimulate glandular secretion of hormones and influence the nervous system which sends mental messages throughout all of your body organs, limbs, etc. Minerals are able to nourish your body to prevent irritability and help in the contractibility of muscles.

We must supply minerals to the body daily, as they are vitally necessary to conserve and help recondition blood, bones, brains, hair, heart, muscles, nerves, and teeth. All of them are imperative to gland functions. They are also required for the development, health, vigor, and efficient operation of many other parts of the body. They are essential for adequate blood circulation as well as for good heart and blood vessel tone.

Since healthy blood needs to be more alkaline than acid, minerals are needed in order to perform this delicate balance by adding proper amounts of copper and iron.

When mineral deficiences accumulate, the bones become brittle and break easily, teeth go bad, and brain cells and the heart muscle do not perform their functions properly. Unless there is a constant daily intake, the blood will withdraw minerals from the tissues and bones. It was not realized until recently that mineral deficiencies also caused a depletion of strength and virility.

The average American's diet is nearly always meagerly supplied with minerals, due to the widespread processing of foodstuffs. Therefore, you must be sure to eat foods containing calcium, iron, phosphorus, potassium, and sulphur . Trace minerals, such as iodine, nickel, and silver, are also being more and more generally acclaimed for the important services they render the body.