|
Vitamin A is important for various functions in the body including normal cell division, growth, good vision and an efficient immune system. Carotenoids are powerful antioxidants.
Vitamin A: In-depth
Vitamin A is a fat-soluble vitamin. It is important for growth, reproduction and for keeping the skin healthy.
Vitamin A is indispensable for good vision as it plays a decisive role in the transformation of light into electrical nerve impulse. Vitamin A is used in all vision-related processes.
Vitamin A (retinol) can only be found in a natural form in animal tissue. Plant foods only contain the precursor form of vitamin A which is called beta-carotene along with ca. 300 other carotenes. These carotenoids, (provitamin = vitamin in its precursor form) are converted into vitamin A in the intestinal mucosa if the body requires it. As opposed to vitamin A, unconverted carotenoids have anti-oxidative properties which mean that they destroy free radicals thus decreasing the risk of getting cancer and protecting the skin from UV-radiation.
240 - 540 mg of vitamin A are stored in the body most of which goes to the liver. This amount lasts for several months.
Besides supplying the body with vitamin A, beta-carotene also plays an important role as an antioxidant. Natural sources of beta-carotene can help to decrease the risk of getting certain types of cancer. However, this does not seem to apply to foods added with beta-carotene.
It is important to know that vitamin A is sensitive to oxygen, acid and light. It is not sensitive to heat.
Vitamin A: Requirements, deficiency, oversupply
Recommended intake of vitamin A according to the DGE* |
Age |
Men |
Women |
19 - 25 |
1,0 mg |
0,8 mg |
25 - 51 |
1,0 mg |
0,8 mg |
51 - 65 |
1,0 mg |
0,8 mg |
over 65 |
1,0 mg |
0,8 mg |
*Deutsche Gesellschaft für Ernährung - a German Nutrition Society.
Vitamin A deficiencies do not occur often in industrialised countries. If they do occur, they are usually linked to alcoholism.
A vitamin A deficiency can lead to night blindness, flaking and drying up of the skin and the mucous membranes.
Overdoses of vitamin A can cause precarious health problems. Exceeding the storage capacity of the liver as a result of an acute of chronic overdose can result in vitamin A poisoning. This can have serious consequences such as headaches, skin changes, bone changes and bleeding. A high consumption of vitamin A during pregnancy can cause birth defects. Pregnant women should therefore not take more than 3000 µg of vitamin A (do not eat liver!).
Carotene is not toxic, even if it is consumed in larger amounts. At worst, it can turn the skin to a yellowish colour.
Antibiotics, laxatives and certain cholesterol lowering medications can inhibit the absorption of vitamin A.
top  |
Vitamin A in food
Vitamin A is only found in animal tissues (e.g. liver, pollock) and animal products (e.g. milk, eggs, butter).
Carotenoids or provitamins are only found in red-orangey or green vegetables (e.g. carrots, tomatoes, broccoli, spinach) which can be converted in the body into vitamin A if need be.
Provitamins are only partly as effective as vitamin A and so for this reason most vitamin tables will show how much vitamin A is needed for the same effect (Retinol equivalent).
Vitamin A in 100 g food:
Liver: 9,500 - 39,100 µg
Curly kale: 1,447 µg
Carrots: 1,700 µg
Smoked eel: 940 µg
Pumpkin: 833 µg
Watercress: 823 µg
Dog roses: 800 µg
Honey dew melon: 783 µg
Savoy cabbage: 783
Lamb's lettuce: 663 µg
Butter: 653 µg
Chicory: 572 µg
Tuna: 450 µg
Units: 1,000,000 µg = 1 g
The nutritional value of beta-carotene in food is dependant on the method of preparation. Beta-carotene is fat-soluble, therefore it is ideal to prepare the meal with a little bit of oil or milk. This also makes the beta-carotene easier for the body to absorb. Beta-carotene cannot be absorbed from raw vegetables such as potatoes. It is therefore recommended to cut carrots into small piece before steaming them briefly.
top
The Complete Book of Food Counts, 9th Edition: The Book That Counts It All
Earl Mindell's New Vitamin Bible,
Earl Mindell, Hester Mundis
Prescription for Nutritional Healing, Fifth Edition: A Practical A-to-Z Reference to Drug-Free Remedies Using Vitamins, Minerals, Herbs & Food Supplements, Phyllis A. Balch CNC
|
