Vitamin A

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Nutrients
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Vitamin A

Postby Nutrients » Feb 12, 2007 4:30 pm

Vitamin A

Vitamin A is an essential human nutrient. It may be found in any of these forms:

Retinol, the animal form of vitamin A, is a yellow fat-soluble, antioxidant vitamin with importance in vision and bone growth, it belongs to the family of chemical compounds known as retinoids.

Other retinoids, a class of chemical compounds that are related chemically to vitamin A, are used in medicine.

Carotenoids or other substances that enable the body to synthesize retinoids. Carotenoids are organic pigments that are naturally occurring in plants and some other photosynthetic organisms like algae, some types of fungus and some bacteria.


Health benefits of vitamin A
Vitamin A is a group of compounds that play an important role in vision, bone growth, reproduction, cell division, and cell differentiation (in which a cell becomes part of the brain, muscle, lungs, blood, or other specialized tissue.) .Vitamin A helps regulate the immune system, which helps prevent or fight off infections by making white blood cells that destroy harmful bacteria and viruses Vitamin A also may help lymphocytes (a type of white blood cell) fight infections more effectively.

Vitamin A promotes healthy surface linings of the eyes and the respiratory, urinary, and intestinal tracts. When those linings break down, it becomes easier for bacteria to enter the body and cause infection. Vitamin A also helps the skin and mucous membranes function as a barrier to bacteria and viruses.

Food sources.

Fortified foods such as fortified breakfast cereals also provide vitamin A.
Provitamin A carotenoids are abundant in darkly colored fruits and vegetables
Vitamin A is contained in fortified breakfast cereals, whereas major contributors of provitamin A carotenoids are carrots, cantaloupes, sweet potatoes, and spinach.

Recommended Dietary Intake for Vitamin A (Retinol) daily values:

Code: Select all

Age           Vitamin A (Retinol) (mcg/day)
0 to 6 months    400
7 - 12 months    500
1 to 3 years     300
4 to 8 years     400

Males
9 to 13 years    600
14 to 51+ years  900

Females
9 to 13 years    600
14 to 51+ years  700

pregnancy        770
lactation       1300



Tolerable Upper Intake Levels (ULs) for Vitamin A(retinol).

Taking amounts higher than those listed below is dangerous for heath.
Beta Carotene taken from vegetable sources don't have an Upper Intake Level limit.

Code: Select all

Age      Children    Males    Females   Pregnancy    Lactation
(years)     (mcg)       (mcg)    (mcg)     (mcg)    (mcg)
0-1       600
1-3       600
4-8       900
9-13      1,700
14-18                 2,800     2,800     2,800         2,800
19+                   3,000     3,000      3,000        3,000




Vitamin A deficiency.

Night blindness is one of the first signs of vitamin A deficiency. In ancient Egypt, it was known that night blindness could be cured by eating liver, which was later found to be a rich source of the vitamin. Vitamin A deficiency contributes to blindness by making the cornea very dry and damaging the retina and cornea.

Vitamin A deficiency diminishes the ability to fight infections. In countries where such deficiency is common and immunization programs are limited, millions of children die each year from complications of infectious diseases such as measles In vitamin A-deficient individuals, cells lining the lungs lose their ability to remove disease-causing microorganisms. This may contribute to the pneumonia associated with vitamin A deficiency

Important to Know
Vegetarians who do not consume eggs and dairy foods need provitamin A carotenoids to meet their need for vitamin A. They should include a minimum of five servings of fruits and vegetables in their daily diet and regularly choose dark green leafy vegetables and orange and yellow fruits to consume recommended amounts of vitamin A.

What are the health risks of too many carotenoids?


Provitamin A carotenoids such as beta-carotene are generally considered safe because they are not associated with specific adverse health effects. Their conversion to vitamin A decreases when body stores are full. A high intake of provitamin A carotenoids can turn the skin yellow, but this is not considered dangerous to health.

Beta-carotene and cancer
It has been shown in trials that the use of synthetically-produced beta carotene (that is, beta carotene in supplement form such as the pills typically sold in stores) increases the rate of lung cancer and prostate cancer, and increases mortality in smokers. These results have been observed in beta carotene supplements synthetically made and not in foods with naturally occurring beta carotene. On the contrary carotenoid-rich fruits and vegetables are known to lower lung cancer rates.

Vitamin A and osteoporosis
One small study of nine healthy individuals in Sweden found that the amount of vitamin A in one serving of liver may impair the ability of vitamin D to promote calcium absorption.
It was found that a dietary retinol(animal source of vitamin A) intake greater than 1,500 mcg/day (more than twice the recommended intake for women) was associated with reduced bone mineral density and increased risk of hip fracture as compared to women who consumed less than 500 mcg/day
There is no evidence of an association between beta-carotene intake, especially from fruits and vegetables, and increased risk of osteoporosis. Current evidence points to a possible association with vitamin A as retinol only.


Vitamin A on ods.gov

Carotene on wikipedia

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AndyBa
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Postby AndyBa » Mar 10, 2008 2:16 pm

I just want to add that:

1.) 100g of fresh carrot contains a daily amount of beta-carotene.
2.) Exposure to sun or other UV rays destroys vitamin A in the body so, while sun bathing, drinking Fresh carrot juice is a good practice. Not only it will maintain your health but the tan will have a nicer color because of the pigments contained in the carrot.
3.) Don't be afraid to eat too much fruits and vegetables containing beta-carotene, unlike vitamin A from animal products the body converts as much beta-carotene to vitamin A as is needed by the body.

Vegan Products Rich in Vitamin A (beta-carotene)

markwilson419
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Re: Vitamin A

Postby markwilson419 » Sep 28, 2010 11:07 am

Thanks for sharing the information on the Vitamin A. I like your post.

meign
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Re: Vitamin A

Postby meign » Oct 11, 2010 1:47 am

Thank you so much Andy... This will surely help me a lot... I hate bringing umbrella even at 12noon... And also trying to avoid my Godmother at morning snack and afternoon snack time for giving me fresh carrot juice, now I know that I should be present during snack time...

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expialidocious
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Re: Vitamin A

Postby expialidocious » May 25, 2018 9:27 am

Nutrients wrote:
Fortified foods such as fortified breakfast cereals also provide vitamin A.

I was just looking into what the source of such fortification might be. Not that I was seeking a fortified food or drink, but since some things (like pineapple juice) list added vitamin A on the label, it's a wonder.

From the book The Vitamin A Story:
Preface :study: Only in the last twenty years has it been possible to define vitamin A deficiency as a nutritionally acquired immune deficiency syndrome... Studies have demonstrated that, in the long run, periodic vitamin A supplementation reduces deaths among pre-school age children in developing countries by about 25%. On the recommendation of the World Health Organization and UNICEF, more than one hundred countries worldwide now have implemented programs that give vitamin A to children. More than two million lives have been saved through these programs.

Vitamin A for food fortification

The biochemical form of vitamin A that is most commonly used for food fortification is retinyl palmitate (vitamin A palmitate). Chemically, it is the ester of retinol (vitamin A) and palmatic acid. This form of vitamin A is relatively stable and is well absorbed. Historically, the Swiss company Hoffman-La Roche was the world's only major supplier of retinyl palmitate, but starting in the late 1990s, the number of commercial laboratories worldwide that synthesize retinyl palmitate has grown tremendously. India alone has several private companies that manufacture vitamin A.


From the book Veganissimo A to Z:
Retinyl Palmitate

Mostly synthetic/vegetable, can also be from living or killed animals. Compound of retinol and palmatic acid. Is the most abundand natural form of vitamin A in animal tissues. Industrial production primarily from synthetic retinol and palmatic acid. Skin conditioner in cosmetics. Active agent in medication, e.g. for treating vitamin A deficiency, in eye and nasal drops and tear substitutes.


From the USDA document Nutrient Vitamins and Minerals, Handling/Processing:
Manufacturing Description

Vitamin A (retinol) is extracted from fish liver oils or produced by total synthesis from [beta]-ionone and a propargyl halide. [21 CFR 184.1930(a)(1)]

Vitamin A acetate is the acetate ester of retinol. It is prepared by esterifying retinol with acetic acid. [21 CFR 184.1930(a)(2)]

Vitamin A palmitate is the palmitate ester of retinol. It is prepared by esterifying retinol with palmitic acid. [21 CFR 184.1930(a)(3)]

Beta-carotene is synthesized by saponification of vitamin A acetate. The resulting alcohol is either reacted to form vitamin A Wittig reagent or oxidized to vitamin A aldehyde. Vitamin A Wittig reagent and vitamin A aldehyde are then reacted together to form beta-carotene. [21 CFR 184.1245]

Discussion... Conversion of tocopherols to tocopherol acetate or palmitate is a synthetic process. Similarly, retinol (Vitamin A) isolated from fish liver oil is converted to retinol acetate or retinol palmitate by chemical processes. However, much of the retinol for human use is produced by total chemical synthesis.


From a Wikipedia article on Hypervitaminosis A:
Hypervitaminosis A results from excessive intake of preformed vitamin A. Children are particularly sensitive to vitamin A, with daily intakes of 1500 IU/kg body weight reportedly leading to toxicity. Preformed vitamin A absorption and storage in the liver occur very efficiently until a pathologic condition develops. When ingested, 70-90% of preformed vitamin A is absorbed and used. Provitamin carotenoids - such as beta carotene - are "largely impossible" to cause toxicity, as their conversion to retinol is highly regulated.


So the vitamin A in fortified foods is likely to be more of a vegan ingredient (than fish), although it shouldn't be eaten excessively (or there can be vitamin poisoning). "In general, a normal, healthy adult must take at least 100,000 IU of vitamin A daily for a period of months in order to display any signs of toxicity", says the Real Vitamin and Mineral Book. However, since the signs of toxicity include blurred vision and muscular incoordination, I suppose it could cause a deadly accident before poisoning one to death (other than children, or adults with health conditions). I think it's great that so many lives have been saved with fortification, yet a warning label on fortified foods or supplements might save a few more. "Chronic toxicity could occur in an individual who commonly consumes supplements or frequently eats foods with high vitamin A content, such as liver, and can lead to severe liver damage"... What do you know, eating liver can cause liver damage, maybe that's poetic justice, but people could be eating too many fortified foods too, as another study estimates, this would be especially in addition to other sources or supplements.


 


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