Vitamin
Structure and Function
Vitamin A was first found and researched in 1913 by McCollum and Davis. What they first found out was that rats raised on a fat-free diet were not healthy. They also found that the ether extract portion of eggs or butter will cure the rat's problems. At first, they thought that it was the fat that cured the rats and therefore was the nutrient.
Then in 1922, Mori found out that is was the lack of a fat-soluble factor that was the problem.
Vitamin A is a fat soluable molecule that has many functions within the body.One of its main roles is to make retinal. Retinal is used in the cones and rods withinthe eyes. Without retinal, you would be blind. Vitamin A is one of the most useful and most important vitamins that the body needs in its daily functions.
It occurs in a preformed state and acts as a precursor. There are three forms of vitamin A :
Retinol (trans)- actual vitamin A
Retinal (dim light vision)-aldehyde
Retinoic Acid (acid)
The function of vitamin A is mainly through its participation in the Vision Purple Cycle in the retina.
In most foods, vitamin A is found in the form of retinol. All three of these forms of vitamin A can be formed from plant pigments and carotenes. Carotenes are the precursor for all the three forms of vitamin A. The most common form is beta-carotene.
The absorbtion and metabolism of vitamin A requires bile salts and is stored within the liver.Vitamin A enters the body and into the blood circulation via chylomicron and then is taken to the liver or the intestine for conversion of the vitamin A. This process requires transport proteins to deliver vitamin A from one place to another within the body. These proteins are called Retinol Binding Protein (RBP). They are essential for mobilizing vitamin A from the liver to the rest of the body. The digestion and absorption of vitamin A is the same as it is for lipids. The component for this is in micelle.
Vitamin A is the only vitamin that can be stored within the body. In most adults, vitamin A can be stored up to a year.
Vitamin A is easily damaged and loses its activity. The activity of vitamin A relies on its double bonds which can be easily oxidized. Antioxidants (such as vitamin E) can be added to feed to protect vitamin A from oxidation.