Vitamin A is the first vitamin discovered by scientists. It is a family of natural compounds called Retinal, Retinol and Carotenoids (Beta-Carotenes). The Retinal and Retinol groups are called "preformed vitamins", which means they are the active forms of Vitamin A that are found only in animal sources. Because of its biologic active form, "preformed Vitamin A" can be used by the body directly from food. The Carotenoids on the other hand, are precursors or compounds that can be converted into active forms of Vitamin A. Carotenoids are made up of fat-soluble pigments in dark yellow and dark green vegetables and fruits. In reality, Vitamin A enters the body in two forms as: 1) preformed Vitamin A, and 2) precursor Carotenoids.

Functions

Many scientists described Vitamin A as the most versatile vitamin. It is because of the multiplicity of its function. The foremost and important role of Vitamin A is for eyesight in such a way that a Vitamin A compound is required in the transformation of the light's reception in the retina to be assimilated by the brain to convey a picture. For example, the signal transmitted by the nerves to convey different colors requires a specialized type of light-sensitive cells (cones). Another set of cells (rods) are required by the eyes, to adapt to the intensity of light, thus allowing the eyes to accommodate and adjust to see bright light at night. These rods and cones are nourished by protein molecules and retinal pigments of the eye which are derived from Vitamin A.

Vitamin A helps protect the skin and tissues inside and outside of the body. It helps keep the smooth surface in the linings of the mouth, stomach and intestines; the linings of the lungs; the linings of the urinary bladder and other reproductive organs; the linings of the eyelids and sinus passageways. For example, specialized (epithelial) cells in the lungs provide mucus that serves as the coating to smoothly sweep infective organisms out of the body.

Other important functions of Vitamin A:

• For growth and formation of strong bones (including teeth) and soft tissues.
• Vitamin A works to resist infection by keeping the immune system strong and healthy.
• Vitamin A also acts as an antioxidant (prevents the formation of cancer cells)
• May help prevent liver damage from toxic chemicals
• Essential for normal reproduction (by having healthy reproductive organs)
• Good stress response and metabolism
• Normal function of the nervous system
• Formation of normal blood cells

Vitamin A is a fat-soluble vitamin which means that the body can only absorb them with the help of fat in the diet. Therefore, if a person has a medical condition that affects the absorption of fat in the body, Vitamin A absorption is also affected, thus resulting in a deficiency. For people who have a Vitamin A deficiency (due to prolonged intestinal problems that alter fat absorption), supplementation of Vitamin A (pills) is important. This is because some Vitamin A pills contain a certain form called "retinyl palmitate" that does not require fat for the body to absorb. It is important however, that using supplementation of this kind is kept under your doctor’s guidance because Vitamin A can be toxic in the body if taken in an excess amount. In addition, it is also important that you know if this form of Vitamin A is really in the pill that you are buying. Therefore, I suggest to check the ConsumerLab.com’s (1) "passed list" because as mentioned in this web site, they investigate the validity of the claims made by the supplement industry.

Deficiencies

• Cancer
• Skin problems called "Xeroderma" and "Follicular Keratosis"
• Blindness/Night Blindness
• Poor growth, weight loss
• Loss of appetite due to hardening (tissue damage) of the taste buds
• Bone and teeth deformities (crooked teeth).

Toxicity

In adults, an excess intake of 50,000 IU to 100,000 IU of Vitamin A over a long period of time can be toxic to the body. Reported toxicity symptoms include nausea, vomiting, joint pain, abdominal discomfort or pain, liver enlargement, dry and cracked lips, bone deformities, itching, hair loss and many more. Other reports also indicate that toxicity occurs in children with intake of 25,000 IU of Vitamin A, resulting in delayed growth.

The Recommended Dietary Allowances (RDAs)

Vitamin A is stored mostly in the liver where it is readily available for transport (via the bloodstream) to the body cells. The RDAs for Vitamin A are expressed in Retinol Equivalent (RE) or International Unit (IU). The RDAs average recommendation to get an adequate amount of Vitamin A is 1000 RE for average male, and 800 RE for average female.

Food Sources

Food sources of Vitamin A is strongly recommended over the supplements (pills). According to researchers, certain foods, such as dark green vegetables contain substances called "Canthanxanthin and Lycopene" that are not found in the supplements, and these substances may prevent cancer.

-- Ofelia B. Mutia, M.S.,R.D.,L.D.

Resources and Acknowledgments

1. ConsumerLab.com - independent tests of herbal, vitamin, and mineral supplements
2. The Essential Guide to Vitamins and Minerals by Elizabeth Somer, M.A.,R.D.
3. Nutrition Concepts & Controversies by Hamilton, Whitney & Sizer
4. Advanced Nutrition and Human Metabolism by James L. Groff, Sareen S. Gropper
5. Bowes & Church's Food Values of Portions Commonly Used by Jean A.T. Pennington, Ph.D., Anna De Planter Bowes, Helen N. Church
6. Essentials of Nutrition and Diet Therapy by Sue Rodwell Williams