Vitamin A

Vitamin A is a fat-soluble vitamin that is essential for a variety of functions in the body, including maintaining good vision and a healthy immune system.

DESCRIPTION

Vitamin A is an essential dietary vitamin whose main storage site in the body is in the liver. Vitamin A is available in foods such as liver, kidney and dairy products, but certain fruits and vegetables contain very high levels of a substance called beta-carotene. Beta-carotene is absorbed by the body and is easily converted into Vitamin A. Vitamin A is converted into a number of active chemicals that perform different roles in the body. The body first makes retinol, which can be turned into retinal to be used in vision and reproduction or retinoic acid to be used in the growth and development of cells.

Vitamin A is important for many functions in the body, including:

· Vision. Vitamin A is essential for healthy eyes. This vitamin is particularly important for vision in dim light and Vitamin A deficiency can cause a condition called night blindness.

· Skin Conditions and Membranes. Retinoic acid (an active form of Vitamin A) slows down the production of a skin protein called keratin. Excess keratin production can cause skin diseases such as acne and psoriasis. Vitamin A is also essential for the health of membrane tissues. Membrane tissues are 'lining' tissues that produce mucus (e.g. the intestines, the urinary tract, the sinuses).

· Wound Healing. A deficiency in Vitamin A can retard the development of collagen in the body that is required for effective wound healing.

· Immunity Against Infection. Vitamin A deficiency can increase the chances of infection. An adequate intake of Vitamin A improves the production of antibodies, which are specialised body proteins that fight specific infections.

· Antioxidant Properties and Tissue Repair. Vitamin A is an antioxidant, which is a chemical that prevents damage and premature ageing by destroying toxic chemicals called free radicals. Free radicals are produced during infection, inflammation, stress and when toxins such as alcohol have been consumed. Vitamin A is important for wound healing, as it promotes the growth of the new tissue that replaces dead and damaged areas of the body.

· Cancer Prevention. Free radicals in the body can damage DNA, thus increasing the risk of cancer. Some forms of Vitamin A may actually protect the cells of the body against free radical damage and thus help to protect against certain cancers.

· Other Uses. Vitamin A is used by the body in the formation of sperm and the maintenance of the placenta and is essential for foetal development.

DEFICIENCY

Vitamin A deficiency can cause serious health problems. Vitamin A is a fat-soluble vitamin, so diseases that interfere with the absorption of fats from the gut can cause Vitamin A deficiency. These conditions include inadequate production of bile fluids, under-production of digestive enzymes by the pancreas, sprue, Crohn's disease and some types of liver cirrhosis. Vitamin A deficiency can cause night blindness and eye diseases, breathing problems and an increased risk of respiratory infection, skin lesions and dry, scaly skin, abnormal production of sperm, infertility, diarrhoea and an impaired sense of taste and of smell.

SOURCES

Vitamin A is found in animal products such as liver, fish-liver oils, eggs and full fat dairy products. Dark-green vegetables and deep-yellow fruits and vegetables provide Vitamin A as well as beta-carotene (which is converted into Vitamin A by the body). The Vitamin A content of foods can be lost during preparation, cooking or storage procedures. To maximise the amount of Vitamin A that can be derived from foods, take the following steps:

· Serve fruits and vegetables raw whenever possible.

· Keep vegetables and fruits covered and refrigerated during storage.

· Steam vegetables and braise, bake or broil meats instead of frying, as some Vitamin A is lost in the fat during the frying process.

DOSAGE

Vitamin A is deposited in the body's fat stores, so it can build up to toxic levels in the body. This is especially important for pregnant women, as Vitamin A has been shown to cause spontaneous abortion and birth defects when taken in excess. The recommended daily intake (RDI) for Vitamin A is 750 Retinol Equivalents (RE) or 3750 IU for adult men and adult women, including those that are pregnant. Women who are breastfeeding require an additional 450 RE per day. Higher dosages are taken for Vitamin A deficiency and medical problems. A medical practitioner should supervise doses higher than the recommended daily intake. Vitamin A toxicity can cause dryness and scaling of the skin, fatigue, headache, loss of body hair and brittle nails. If in any doubt ask your health professional for advice.

NOTES

Vitamin A and its related chemical, beta carotene, are thought to reduce the risks of cancer in most people, however, there is some evidence to suggest that a high intake of beta carotene in people who smoke may actually increase the risk of certain cancers. This may be because the toxic chemicals that are produced by smoking can damage the beta-carotene in the body and convert it into a chemical that can harm the body.