Different Forms Of Vitamin A
Vitamin A occurs in many forms, such as retinol (alcohol), retinal (aldehyde), retinyl acetate or retinyl palmitate (esters), and provitamin A carotenoids (b-carotene, a-carotene, etc.). (source)
Vitamin A
Vitamin A is a critical micronutrient, essential for night vision and for the maintenance of skin and mucosal integrity. An early sign of vitamin A deficiency is night-blindness. Severe vitamin A deficiency may result in permanent blindness. Vitamin A deficiency is still a major nutritional problem in Indonesia as well as in many other parts of the world. The main intervention programmes against vitamin A deficiency administered by the Indonesian government are nutrition education, distribution of vitamin A capsules, and fortification of selected widely consumed foods.
Fortification of foods with vitamin A has been shown to be a very promising strategy. A pilot project on vitamin A fortification of monosodium glutamate (MSG) in three provinces has resulted in reduction of the prevalence of vitamin A deficiency. Further developments are dependent on overcoming the colour changes caused by fortification of MSG with vitamin A. Other foods, such as palm oil and noodles, have also been considered as carriers for vitamin A.
Vitamin A occurs in many forms, such as retinol (alcohol), retinal (aldehyde), retinyl acetate or retinyl palmitate (esters), and provitamin A carotenoids (b-carotene, a-carotene, etc.).
Vitamin A is relatively unstable under normal storage conditions, particularly in harsh environments. The instability is mostly due to its chemical structure, which contains many double bonds susceptible to degradation (fig. 2).
To minimize the degradation of vitamin A, several approaches have been introduced. Since vitamin A is sensitive to atmospheric oxygen (the alcohol form of vitamin A is less stable than the esters), it is normally available commercially as a preparation protected by a coating that includes antioxidant(s). According to Murphy [3], there has been only one major supplier of vitamin A (as retinyl palmitate or acetate) for food fortification, Hoffman-La Roche of Switzerland. Table 1 lists the major formulations that are or have been available.
Antioxidants that maybe added to vitamin A premixes are butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and a-tocopherols (vitamin E). The use of vitamin E as an antioxidant is gaining popularity. Trace metals (especially iron and copper) and ultraviolet light accelerate the degradation of vitamin A. The stability of vitamin A is also affected by acidity. Below a pH of 5.0, vitamin A is very unstable.
FIG. 2. Chemical structure of vitamin A alcohol and b-carotene
TABLE 1. Commercial vitamin A preparations available from Hoffman-La Roche
|
Type |
Ingredients |
Food application |
|
250 CWS |
Retinyl palmitate, acacia, sugar,
modified food starch, BHT, BHA, sodium benzoate, a-tocopherol |
Non-fat dry milk, dehydrated foods, dry
cereals, beverage powders to be reconstituted before use |
|
250 S |
Retinyl palmitate, gelatin, sorbitol-modified
food starch, sodium citrate, corn syrup, ascorbic acid, coconut oil, BHT,
a-tocopherol, silicon dioxide, BHA |
Dry mix and fluid milk products |
|
250 SD |
Retinyl palmitate, acacia, lactose,
coconut oil, BHT, sodium benzoate, sorbic acid, silicon dioxide, BHA |
Foods and baked products, dehydrated
potato flakes, dry milk |
|
500 |
Retinyl palmitate, gelatin, invert
sugar, tricalcium phosphate, BHT, BHA, sodium benzoate, sorbic acid,
sodium bisulphite |
Dry mix and fluid milk products |
|
Emulsified RP |
Sucrose - retinyl palmitate emulsion in
water |
Tea leaves |
|
Oil |
Retinyl palmitate, BHA, BHT |
None |
Source: ref. 4.
Abbreviations: BHT, butylated hydroxytoluene; BHA, butylated hydroxyanisole;
CWS, cold water soluble; RP, retinyl palmitate.
Vitamin A
 |
Vitamin A is fat soluble, it is an antioxidant and occurs
in two forms - retinol and carotene. The RDA [Food and Nutrition Board,
National Academy of Sciences - National Research Council - Recommended Dietaty
Allowances. ] for adults is 1000 micrograms RE (Retinol Equivalents. 1 RE = 1
microgram retinol or 6 micrograms §-carotene).
The allowances, expressed as average daily intakes over time, are intended to
provide for individual variations among most normal persons as they live in
the United States under usual environment stresses.
Because vitamin A and carotene exist in more than one chemical form, and
because they are not equally active, it is usual to give the name retinol to
the pure vitamin A. Thus the total vitamin A activity of a food, its retinol
equivalent, is determined by how much it contains of retinol, chemicals very
similar to retinol but not as active, and a range of carotenes also of varying
activity.
Vitamin A maintains the skin and mucous membranes. Promotes growth, strong
bones, healthy skin, hair, teeth and gums. Builds up resistance to respiratory
infections and shortens the duration of diseases. It counteracts night
blindness and aids in the treatment of many eye disorders. Night blindness is
an early symptom of a deficiency of vitamin A.
In a dozen case-control and cohort studies, intakes of fruits and vegetables
containing carotenoids has been associated with a reduced risk of lung cancer.
In contrast little relationship has been found between intake of preformed
vitamin A (retinol) and this disease.
Available data thus strongly support the hypothesis that dietary carotenoids
reduce the risk of lung cancer, but the data also are compatible with the
possibility that some other factor in these foods is responsible for the lower
risk. The recommendation to eat a variety of fruits and vegetables is
reasonable, but leaves much to chance; if ß-carotene is the anticancer agent,
intake of specific fruits and vegetables should be advised.
The best natural sources are green leafy vegetable tops, carrots, red peppers, sweet potatoes, yellow fruits, apricots, fish-liver oil and eggs.
Vitamin A is one of the few vitamins in which excess produces definite and severe effects. Toxic symptoms can occur with intake exceeding 100 000 IU's daily. Hypervitaminosis A leads to loss of appetite, a dry, itchy skin often with peeling, intense headaches and an enlarged liver. Recovery is fairly rapid when intake is reduced.
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