Vitamin A

What is it?

The term Vitamin A refers to a family of fat soluble dietary compounds similar to retinol. It is stored primarily in the liver. Vitamin A is found in foods as itself or as a precursor which is converted to Vitamin A in the body. The precusors known as carotenes are found in yellow, green and red coloured plants.

Food sources

Preformed Vitamin A is cheifly found in liver, red meat and eggs. It is also found in fish, milk, butter and cream. Carotenoids are found in green leafy vegetables as well as orange and red fruits and vegetables.

Main actions

Vitamin A is an essential nutrient required for life. It is a powerful antioxidant and is essential for embryonic growth. Vitamin A maintains the health of epithelial cells in the body which forms an important barrier to infection and immune system function.

It is essential for vision as it forms retinaldehyde, the substance responsible for the light sensitive part of the retina and also retinoic acid which helps with the correct functioning of the cells which prevent damage from exposure to the environment.

The antioixidant properties of Vitamin A are also considered to provide an anticancer action.

Clinical use

Traditionally supplementation with Vitamin A has been used to treat or prevent deficiency in conditions assoicated with risk of Vitamin A deficiency such as diabetes, hyperthyroidism, protein deficiency, intestinal infections and cystic fibrosis.

It is used in paediatrics to reduce the severity of childhood illnesses in particular measles, croup and otitis media.

Anti cancer

Vitamin A and its derivatives have been used in dermatology with psoriasis, acne, lichen planus, skin cancers and UV induced skin damage.

Measles related night blindness.

Note: It is important to note that beta carotene found naturally in plants is not associated with the teratogenic effects of Vitamin A toxicity. The dosage range of 10000 to 50000 i.u. daily is not recommended for long term use.

Note: It is not recommended for pregnant women to take supplements containing Vitamin A as excessive doses have been shown to be teratogenic.



Important drug reactions

Cholestyramine reduces Vitamin A absorption
Oral contraceptives and statin drugs may increase serum levels of Vitamin A