vitamin descriptions

The vitamins information pages - Vitamin A
==========================================

Description vitamin A
---------------------

Vitamin A is a group of fat-soluble substances that are found in
animal products. These substances include retinol (an alcohol) and
retinal (an aldehyde). Retinal is responsible for production of an
acid that affects gene transcription. By means of cellular
differentiation, physiological roles of cells are specialized. Vitamin
A also includes carotenoids, which are produced by plants. These are
transformed to retinal. Fruits and vegetables for example contain
beta-carotene, which is converted to vitamin A in the human body.

Functions of vitamin A
----------------------

Vitamin A is essential for the development of bones, skin and
eyesight. It strengthens the immune system, creating resistance to
infection and disease. It also regulates growth by regulating the
expression of the growth hormone gene. When vitamin A deficiency
occurs, a person may suffer from night blindness (caused by inadequate
retinol supply), dry skin, poor growth and developmental difficulties.

Vitamin A in food
-----------------

Food sources that contain retinol and retinal are animal products,
including: liver, kidney, oily fish, dairy, eggs and margarine.
Carotenoids are found in oranges, yellow, orange and dark green
vegetables and fruits (for example carrots, broccoli, spinach and
watercress).

Vitamin A as a supplement
-------------------------

Vitamin A is recommended therapeutically for patients experiencing
skin conditions (eczema, acne, psoriasis) and night blindness. It also
prevents ulcers, respiratory disease, menstruation cramps or urinary
problems, because of its beneficial impact on the immune system.
Vitamin A plays an important role in the prevention of several types
of cancer.

Interactions
------------

Zinc deficiency interferes with the vitamin A metabolism as a result
of decreased retinol synthesis and decreased retinol to retinal
transformation. When vitamin A is used in combination with iron
anaemia is less likely to occur.
Chronic alcohol consumption results in depletion of vitamin A storage
in the liver. this contributes to alcohol-induced liver damage.

Warning
-------

Vitamin A is not recommended for pregnant women. Excess vitamin A may
cause birth defects. However, an adequate supply of vitamin A is still
required because of its essential role in embryonic development.

Overview vitamin information

Descriptions of vitamins on this website are based on information
provided by BBC Health and The Linus Pauling Institute.

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