First : What is vitamin A and where does it come from?
Vitamin A is structurally related to carotene.
Carotene is converted into vitamin A (a safe source of vitamin A) in the liver, One molecule of beta carotene equals two molecules of Vitamin A. Vitamin A is manufactured by extraction from fish-liver oil and by synthesis from beta-ionone. Vitamin A is carried through the body by fat. The body can store this type of vitamin in fat tissue.
How do we receive A
The body obtains vitamin A in two ways.
1. manufacturing it from carotene, (a vitamin found in such vegetables: carrots, broccoli, squash, spinach, kale, and sweet potatoes).
2. The other is by absorbing ready-made vitamin A, from plant-eating organisms. (beef, calf, chicken liver; eggs, and fish liver oils as well as dairy products including whole milk, whole milk,yogurt, whole milk cottage cheese, butter, and cheese.)
Storage of vitamin A is in liver cells, when retinol is needed in other tissues, it is de-esterifed and released into the blood as the alcohol. Retinol then attaches to a serum carrier, retinol binding protein, for transport to target tissues.
What does it do?
Vitamin A is one of the most versatile vitamins, it has many functions: vision, immune defenses, maintenance of body linings and skin, bone and body growth, normal cell development, and reproduction. Vitamin A helps form and maintains healthy teeth, skeletal and soft tissue, mucous membranes, and skin. Thus vitamin A may be important in protecting against conditions related to oxidative stress, such as aging, air pollution, arthritis, cancer, cardiovascular disease, cataracts, diabetes mellitus and infection.
How much to take
The recommended daily allowance (RDA) of vitamin A is 2,670 International Units (IU) (US National Institute of Child Health and Human Development)
The American Food and Drug Administration has established an RDA of 5,000 IU for vitamin A for adults, with a recommendation that pregnant women maintain their intake around 8,000 IU and that vitamin A be taken in the form of beta-carotene, which is not considered toxic.