Vitamin A was the first fat-soluble vitamin to be discovered, utilized and relayed by Egyptians that recognized night blindness, a result of Vitamin A deficiency, could be cured by ingesting liver which stores vitamin A, thus a rich source of vitamin A, though unappealing for most as a therapeutic approach for insufficiency in this element.
There are essentially 3 forms of vitamin A: retinols, beta carotenes, and carotenoids.
Retinol is the most active form and found primarily in animal sources of food.
Beta carotene is the plant source of retinol and the most common source of Vitamin A in humans.
Carotenoids are the largest group of the 3,and contain multiple conjugated double bonds and exist in a free alcohol or in a fatty acyl-ester form.
Deficiency of vitamin A is not a common deficiency in America,but prevalent in malnourished, elderly, and chronically sick populations, and in developing countries. Deficiency presents with abnormal visual adaptation to darkness, or night blindness, dry skin, dry hair, broken fingernails, and increased vulnerability to opportunistic infections. Deficiency can result from inadequate dietary intake, malabsorption, or dysfunctional metabolism. Vitamin A is dependent upon iron for absorption and studies suggest the same in zinc presence. As mentioned earlier, the liver is the main storage for vitamin A and can store up to a year of reserve within its parenchyma. Because vitamin A is a fat-soluble vitamin, any gastrointestinal disease, or surgeries involving the small bowel that result in malabsorption of fat will inhibit the absorption of vitamin A as well.