The Function of Vitamin A in Our Life

Vitamin A is a bi-polar (a second order neuron of the retina) cell that is formed with bonds between carbon and hydrogen and is linked to a family of similarly shaped molecules, the retinoids, which complete the remainder of the vitamin sequence. 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 palmitate.
* other retinoids, a class of chemical compounds that are related chemically to vitamin A, are used in medicine.

Key Functions of Vitamin A

Vitamin A is essential for:

* Vision
* Gene Transcription
* Immune Function
* Embryonic Development and Reproduction
* Bone Metabolism
* Haematopoiesis
* Skin Health
* Reducing Risk of Heart Disease and Cancer
* Antioxidant Activity

It performs a variety of important functions:

* Beta carotene is a powerful antioxidant that neutralizes free radicals - molecules that damage healthy cells - and increases the risk of accelerating the aging process and/or health conditions.
* Vitamin A promotes the growth of strong teeth and bones.
* Fat is used to build new cells and is critical for normal brain development and nerve function.
* Vitamin A is essential for the formation of visual purple, a pigment that allows you to see in dim light.

Food Sources of Vitamin A

Vitamin A is found naturally in many foods:

* liver (beef, pork, chicken, turkey, fish)
* carrots
* Broccoli leaves
* sweet potatoes
* kale
* butter
* spinach
* leafy vegetables
* pumpkin
* collard greens
* cantaloupe melon
* eggs
* apricots
* papaya
* mango
* peas
* broccoli
* winter squash

Recommended Dietary Usage

* Infants (AI) - (0-6 months) - Male 400 (1,333 IU), Female 400 (1,333 IU)
* Infants (AI) - (7-12 months) - Male 500 (1,667 IU), Female 500 (1,667 IU)
* Children - (1-3 years) - Male 300 (1,000 IU), Female 300 (1,000 IU)
* Children - (4-8 years) - Male 400 (1,333 IU), Female 400 (1,333 IU)
* Children - (9-13 years) - Male 600 (2,000 IU), Female 600 (2,000 IU)
* Adolescents - (14-18 years) - Male 900 (3,000 IU), Female 700 (2,333 IU)
* Adults - (19 years and older) - Male 900 (3,000 IU), Female 700 (2,333 IU)
* Pregnancy - (18 years and younger) - 750 (2,500 IU)
* Pregnancy - (19 years and older) - 770 (2,567 IU)
* Breast-feeding - (18 years and younger) - 1,200 (4,000 IU)
* Breast-feeding - (19 years and older) - 1,300 (4,333 IU)

Nutritional Safety

* Toxicity - The condition caused by vitamin A toxicity is called hypervitaminosis A. It is caused by overconsumption of preformed vitamin A, not carotenoids. Preformed vitamin A is rapidly absorbed and slowly cleared from the body. Generally, signs of toxicity are associated with long-term consumption of vitamin A in excess of ten times the RDA (8,000 to 10,000 mcg/day or 25,000 to 33,000 IU/day).
* Safety in Pregnancy - Although normal fetal development requires sufficient vitamin A intake, consumption of excess preformed vitamin A (retinol) during pregnancy is known to cause birth defects.
* Deficiency - Vitamin A deficiency and vision - Vitamin A deficiency among children in developing nations is the leading preventable cause of blindness. Vitamin A deficiency and infectious disease - Vitamin A deficiency can be considered a nutritionally acquired immunodeficiency disease.

My next article entitled "The Function of Vitamin B in our Life" will examine the role of Vitamin B in good nutrition.

See you on the Beaches of the World,

Kevin McNabb

This article will examine the role of Vitamin A in good nutrition.

Information about the Author:

Kevin McNabb is the Founder and Chief Executive Officer of Toronto-based GlobalHealthMgmt.com, he offers live seminars and Internet training programs on personal development for the Network Marketing industry. Details can be seen at www.KevinMcNabb.com. For more information on this article topic, see http://www.globalhealthmgmt.com/Vitamins_Supplements.html

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