Vitamin A

What Is Vitamin A?

Vitamin A is one of the four fat soluble vitamins. It was first isolated in 1913 by American researchers. It is found in foods in two different forms:

  • natural vitamin A, known as retinol (from animal foods)
  • provitamin A, or carotenoids, which can be converted into vitamin A in the body (found in both plant and animal foods). The most important of the carotenoids is called beta-carotene.

Vitamin A is stored in the body and therefore supplies do not have to be restocked on a daily basis as is the case for some other vitamins.

What Does Vitamin A Do For You?

  • It aids night vision - the old saying that "carrots will make you see in the dark" has some scientific basis since carrots are an excellent source of this vitamin.
  • It is essential for continuing healthy eyes and vision.
  • It maintains the body's layers of lining tissues (particularly in the nose, throat, lungs and digestive system) and is important for the proper function of the respiratory system.
  • It helps the growth and maintenance of bones, skin, gums, teeth, nails and hair. In fact, vitamin A is really essential for the healthy maintenance of most parts of the body.

Source

Food Sources for Retinol

Important

  • Liver (100g serving)

Moderate

  • Dairy products - full fat cheese (25g serving), full cream milk (250 ml serving), eggs (1)
  • Fats - butter, margarine (10g serving)
  • Enriched foods e.g. Milo/Ovaltine (10g serving)

Low or Nil

  • Meat (trace)
  • Fish (trace)
  • Fruit
  • Vegetables
  • Cereals
  • Pulses
  • Nuts
  • Skim milk and low fat dairy products
  • Yeast products

Food Sources for Beta-Carotene

Important

  • Fruit (tropical and orange-coloured) — apricots, cantaloupe, mango, pawpaw (100g serving)
  • Vegetables (orange-coloured and green leafy) -carrots, sweet potatoes, broccoli, spinach, pumpkin (50-100g serving)

Moderate

  • Cheese, full fat (25g serving)
  • Fats - butter, margarine (10g serving)
  • Fruit - apples, pineapple, oranges, bananas, berries (100g serving)
  • Vegetables - Brussels sprouts, peas, cabbage,
  • tomatoes, beans, sweet corn (50-100g serving), parsley (5g/2 sprigs serving)

Low or Nil

  • Fish (trace)
  • Potatoes
  • Meat
  • Cereals
  • Pulses
  • Nuts
  • Eggs
  • Yeast products e.g. Marmite

What Destroys Vitamin A?

Vitamin A, including that formed from the carotenoids, is not easily destroyed in the cooking process.

Storage away from light and air helps prevent loss.

There is always loss (about 20%) in the canning of fruit and vegetables. Certain preservatives used in making processed meats (frankfurters, salami) are destructive to vitamin A.

Vitamin A's absorption into the body is blocked by acute protein deficiency or a serious lack of fat in the diet.

Deficiency Problems and Symptoms

Vitamin A deficiency is one of the two most widespread nutritional deficiencies in the underprivileged countries of the world.

"Night blindness", or the inability of the eyes to adjust to darkness, is a major health problem when serious deficiency occurs. Total blindness can occur in advanced cases.

A degenerative disease of the eye's cornea, also leading to blindness, is another result of a deficiency. So are skin complaints and inflammations.

Minor deficiency can cause difficulty in eyesight adjustment on entering a dark room from bright sunlight.

The main symptoms of deficiency are dry, scaly skin, poor sight and eye pain.

Recommended Daily Intake

The recommendation is 750 micrograms which includes both retinol and vitamin A formed from carotenes.

Toxicity

Large doses of vitamin A in its retinol form are highly toxic, even fatal.

Early Antarctic explorers who were forced to eat their husky dogs suffered severe illness and even death due to the high amount of retinol in the dogs' livers.

More than 10,000 micrograms per kilo of body weight per day can induce toxic symptoms that include skin problems, bald patches and liver malfunction.

Although natural vitamin A (retinol) can be toxic in excess, a high intake of carotenes (e.g. in fruit and vegetables) is not dangerous, but skin can sometimes become orange-colored.

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