Vitamin A
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Vitamin A

What is vitamin A

Generally speaking, vitamins belong to the field of micronutrients, a jumbled group of substances that the human organism demands in extremely low amounts and whose involvement in cell metabolism is essential. Otherwise it would be deprived of essential elements in order to carry out chemical reactions that sustain all organic functions.

Vitamin A Ingredient

All vitamins have two things in common: the dependence of the organism in order to receive their external supply since it lack the metabolic processes to synthesize them and to develop a catalyzing function (which is a synonym of both impulse and acceleration) of said biochemical reactions, integrated by the enzymes,

Simultaneously, they are separated in two great blocks, which are classified according to their solubility in water or fat; the first block is for those which are hydro-soluble (like all complex B vitamins and vitamin C), and the second block is for those which are fat-soluble, to which vitamin A belongs.

Table of contents

    1. What is vitamin A
    2. The first evidences of its existence and its evolution
    3. What are its structural, physical, and chemical characteristics
    4. Deficiency of Lack of vitamin A, causes and consequences
    5. Foods rich in Vitamin A
      1. What are the main nutritional sources of vitamin A?
      2. Liver pate from any animal (except from chicken)
      3. Paprika, red pepper, or cayenne pepper
      4. Yam
      5. Carrot
      6. Rapini
      7. Lettuce
      8. Sweet potato
      9. Tomato
      10. Melon
      11. Green leaf vegetables
      12. Pilgrim pumpkin
      13. Dried herbs
      14. Dairy products
      15. Fish and seafood
    6. Important biological properties and organic functions of this vitamin
      1. The functioning of sight
      2. The immune system
      3. Embryo and fetal development
      4. Formation of red cells
      5. The integrity of the epithelium
      6. Anti-cancerous and anti-aging action
      7. Proper development of the nervous system
    7. Its excess can also be harmful: hypervitaminosis A
    8. Intake: How much Vitamin A should we consume, and how
      1. How to manage a proper intake of vitamin A: supplementation
    9. What kinds of vitamin A supplements exist and what are they for?
    10. Possible interactions with other substances

The first evidences of its existence and its evolution

Vitamin A is also known as retinol, a name whose origin lies on the discovery of its ability to generate the necessary pigments for the functioning of the retina and, consequently, of sight.

The discovery of vitamin A was carried out blindly on laboratory animals. Said discovery happened during the second decade of the past century, when a British team of scientists that was led by Gowland Hopkins, found that certain animal species stopped growing if the only source of fat that was present in their diet was lard, while if it was substituted by cow’s butter, without changing the rest of the elements of the diet, the animals developed at a predictable rhythm.

This substance was first called a “milk factor”. Later works with animals developed the information about nutritional sources that manifested similar virtues, such as egg yolk and cod liver oil, which lead to the conviction that they shared a nutrient in common, which was called vitamin A.

Following a chronological order, we are going to illustrate the sequence of findings:

  • In 1913, Mc Collum and Davis from the Hopkins team, argued that the normal growth of laboratory animals required to supplement their diet with a particular lipid that could be obtained from egg yolk or butter.
  • In 1919 the possible origins of this vitamin were expanded, since it could also be found in typically fatty matter, or in plants of an orange tone.
  • In 1930, Moore proved an important chemical relation between carotene and vitamin A, which showed that once the former was ingested, a metabolization process took place inside the body in which it transformed into vitamin A. This finding was an extraordinary advancement in the possibilities to prevent the deficit of this vitamin on human health.

However, it is interesting to point out that, in the age of the Egyptian civilization, it was already known that certain foods possessed a therapeutic power, like the liver in order to prevent certain diseases. The evidence lies on the fact that they treated night blindness with a diet rich in this viscera.

What are its structural, physical, and chemical characteristics

When it comes to its chemical structure, there are two variants of vitamin A: preformed vitamin A, which is found in meat and in the milk of mammals, poultry meat, and oily fish. And pro-vitamin A which is associated to fruit and vegetables; carotenoids, from which beta-carotene is the most abundant, stand out inside this group .

Characteristics of Vitamin A

It is said that the structure of retinol is terpenoid, which means that it is a hydrocarbon formed by five atoms of carbon, several of hydrogen, and one of oxygen, with a beta-ionone ring with a lateral branch and five double links oriented to trans configuration. This has an enormous transcendence when it comes to physical and chemical properties of the substances; we will explain that cis-trans isomerism, which is also called geometrical isomerism, is the kind of spatial organization which is typical of certain hydrocarbons, more specifically of alkenes (simple carbon and hydrogen chains with some double links) and cycloalkenes (carbon and hydrogen rings without double links). In this case, the substituents are on the opposite side of the double link or in the opposite side inside the cycloalkene.

From this molecular structure, we can conclude that both vitamin A and carotenoids are nonpolar compounds, which means that their solubility in fat is optimal. Due to this, vitamin A can be stored in the adipose cells, whose cytoplasm is filled with fatty matter, which is ready to be released when the organism requires it.

This ability to store it justifies the fact that it does not have to be consumed daily, a periodical intake is enough to ensure its stock. In this aspect, it must be said that most of the amount of vitamin A is stored in the liver, some of it ends up in the lungs, the kidneys, and the reserve adipose tissue.

Retinol has, within its chemical composition, two modalities: free alcohol and fatty acid esters, greatly palmitic acid, apart from precursor molecules, which are carotenoids. It is interesting to point out some of the data about the behavior of this kind of substances once they join the organism: more than three quarters of retinol esters are absorbed and go to the bloodstream, while only around half of the beta-carotenes achieve this (however, the amount of fat that is included in the diet affects the rate of absorption). Once they reach the digestion process, some specific enzymes called lipases are in charge of hydrolizing those esters so that the retinol molecule is free to be absorbed in the form of alcohol in order to join metabolic pathways.

Even though the specific denomination of vitamin A corresponds exclusively to retinol, there are a series of substances that are chemically derived such as retinal, 13-cis retinol, and dehydro-retinol, which are attributed the ability to carry out the tasks of the retinol coenzyme, to a greater or lesser degree. From the ones that have been listed, the first two have a vitamin power of 90% and 75% respectively compared to retinol, and it only lowers to 40% in the case of dehydro-retinol.

Carotenoids are much more important than these ones, specially beta-carotene. Even though its value can be placed at a 6th position when compared to retinol, its presence is abundantly widespread among vegetables, which are cataloged as a nutritional and fundamental source of vitamin A. Not in vain, there are countries like the United States where people’s diets lack vegetables, a population whose vitamin A intakes are made of a third of carotenoids.

It should be pointed out, that from the 600 identified carotenoids, they do not reach a mere one tenth of the biological effects that vitamin A produces in the organism. Apart from beta-carotene, alphacarotene and beta-cryptoxanthin are also important. But among the most common ones, some of them lack this effect completely, for example: lycopene (abundant in tomato), zeaxanthin and lutein.

Retinol is a substance whose main feature is a high bioavailability, even in complex foods, in any of its forms: alcohol and ester. Due to its remarkable lipid solubility, it is normally found dissolved in fatty matter even though sometimes it is linked to proteins of intracellular structure, or to those that perform the transport of substances to the bloodstream.

In contrast, carotenoids, which can be found as constituents of some vegetable oils and even in some foods of animal origin (like egg yolk or milk), are mainly dissolved within some compartments of vegetable cells which are specialized in storing pigments called chromoplasts, where they are firmly linked to specific proteins. On the one hand, this link protects them from oxidation, which is obviously an advantage. On the other hand, this diminishes their bioavailability, so that in order for their organic properties to be used, it is necessary to perform the denaturing of the support proteins through heat, which is clearly an inconvenience.

This circumstance explains how a cooked carrot outranks a raw carrot as a vitamin A source.

These carotenoid molecules are quite labile to sunlight, since a considerable amount of them are left unused when the green leaves and the foods that contain them are sun-dried. This is the reason why vitamin A deficiency is often frequent in arid zones, where it is customary to sun-dry edible leaves and vegetables in order to store them and prevent them from rot.

The molecular structure of substances that are granted vitamin A activity have a high degree of unsaturation, which makes them susceptible to oxidation (which is manifested through rancidification) during long periods of transformation and storing of foods.

This oxidation can take place along with the one that unsaturated fatty acids suffer (which integrate fat molecules) or even the one induced by the ultraviolet rays of the solar spectrum.

Another possible retinol breakdown (which is in trans form) is transformed into 13-cis retinol, if it is heated in an environment without oxygen, whose vitamin power does not reach the 75% of the previous one. It can also be done with isomers 11-cis and 9-cis, with a vitamin effect of 25%.

In the case of milk, the heat treatment of pasteurization isomerizes a tiny part of retinol, between 3 and 7%. This percentage rises to 16 in the case of UHT processing, which is the one used for tetrabrick milk, which can even reach a 35 when it is sterilized in a bottle of glass and also in certain types of cheese.

If we move to the processing of vegetable foods through high temperatures, what happens specially with the canning, is that we observe that there are serious reductions of the vitamin value of beta-carotene due to this isomerization phenomenon.

Even though, as it was previously described, it produces a compensatory effect since it increases the bioavailability regarding unprocessed food.

Carotenoids are a very efficient antioxidant agents that face the aggressive action of what is called singlet oxygen, which is formed by the light activation of molecular oxygen from the atmosphere.

What happens is that they simultaneously self-destroy in the same process, which results in the fractionation of the bone marrow and its molecule, the hydrocarbon chain and the formation of carbonylic and epoxide compounds.

Deficiency of Lack of vitamin A, causes and consequences

We can go back to ancient civilizations like Egypt or Classic Greece in order to find references of the clinical effects of the deficiency of this vitamin and its treatment with liver. It is a nutritional anomaly whose awareness can be traced until antiquity, since it is even quoted in the Old Testament.

All those indirect references, since they were not truly aware of the existence of this substance, were attributed to night blindness and xerophthalmia which were caused by a low fat diet.

Vitamin A Deficiency

There are countries where the clinical manifestation of this deficiency in children surpasses a 3%, while the subclinical manifestation without symptoms reaches a 30%. The first number is a truly revealing fact: each year, all around the world, over 100 000 children lose their sight due to this, while the second amount is hard to quantify, but it is known that the efficiency of the immune system decreases and it triggers infections, specially diarrhea and pneumonia.

Fortunately, a deficiency of vitamin A is an unlikely nutritional deficit in advanced societies, but it can become a stiletto within the organism, since it is associated to several pathologies among which, due to their importance, we highlight:

  • Ocular problems: they can result in what is known as night blindness, which is a reduction of visual acuity with the setting of the sun; photophobia, hypersensitivity to sunlight, dryness in the eye with lack of tearing, xerophthalmia, or corneal opacity which is often associated to the formation of ulcers (which are frequently the prelude to blindness).
  • Loss of intensity of the immune response against external agents, which makes the person that suffers from it vulnerable to bacterial, parasite, and viral infections. All of this is due to one of the main tasks of this vitamin, which is to keep the integrity of mucosas intact and to trigger an immune action locally that will provide an exceptional primary barrier against these agents. But this is not the only task of vitamin A in the immune function, since specialized cells of the defensive structure of the organism are also affected by its deficiency; this circumstance promotes an increase in precancerous cells in some epitheliums, particularly in those of the mouth, throat, and lungs.
  • Bone problems: it inhibits the growth of these structures from the endings of the cartilage, which can lead to deformation of the anatomy of bones (like kyphosis, lordosis, etc) and it is a predisposing factor when it comes to suffering arthrosis since it slows down bone regeneration in the joints.
  • Skin problems: one of the immediate consequences of a vitamin A deficiency is hyperkeratosis, a phenomenon by which the skin adopts a harsh, dry, and scaly texture, the skin and hair become fragile and inconsistent.
  • Other symptoms which are more specific can be overall tiredness, lack of appetite accompanied by weight loss, a reduction of hearing, tasting, and smelling sensitivity, and even disorders of the reproductive function.

And finally, an interesting fact to conclude these section:

Its deficiency increases the symptoms of measles, in fact, when a child has a vitamin A deficit, suffering measles will increase fever and diarrhea.

Foods rich in Vitamin A

What are the main nutritional sources of vitamin A?

As it was previously mentioned, this vitamin is present, within its organic nature, in foods of animal origin in a preformed phase, while in many organisms of the vegetable kingdom it appears as pro-vitamin A, which is a generic name that makes reference to carotenes and carotenoids, among which beta-carotene specially stands out.

There is no doubt that the best way to meet the daily recommended intake of vitamin A (and of all vitamins in general) is to include in our diet all kinds of fruit, vegetables, legumes, wholemeal grains, and products of animal origin (specially oily fish, eggs, and dairy products). Vitamin A is naturally found in the composition of plenty of foods and in certain synthetically enriched food, like some types of milk and wholemeal cereals:

  • Liver, is probably the richest source of this substance, even though its consumption must be limited due to its high content in cholesterol. For example, with a portion of a hundred grams of calf or pork liver we would meet abundantly the 600-800 daily micro-grams that the organism requires of this vitamin. Chicken liver is out of the list, since its content in vitamin A is minimal. In order to illustrate it:
  • Pork liver: it contains 36 milligrams per 100 grams
  • Calf liver: less than pork, with 20 milligrams.
  • Pate and foie-gras: its content differs according to how and with what they are elaborated, but it normally moves between 5-8 milligrams per 100 grams.
  • Cod liver oil
  • Certain oily fish, among which salmon stands out.
  • Vegetables with green, orange, and yellow leaves (this feature coincides with vitamin K), such as broccoli, green cabbage, Brussels sprouts, carrots, spinach, lettuce, pumpkin, and courgette. 
  • Some fruit like melon, papaya, apricot, cherries, and mango.
  • Dairy products, both natural and enriched, are the main source of vitamin A in certain developed countries of the world like the United States.
  • Enriched wholemeal cereals.

Liver pate from any animal (except from chicken)

The liver is a gut that is full of vitamins and minerals. To give us an idea, turkey liver provides 75 333 International Units (IU) of vitamin A per 100 grams (which is the highest known quantity of vitamin A in food). In this way, only a spoonful provides 430 IU of vitamin A (9% DV, a measure known as “daily value” based of the recommendations for a diet of 2000 kcal); Again, to give us an idea, the same amount of cod liver would correspond to 500 IU (10% DV)

Paprika, red pepper, or cayenne pepper

A serving of 100 grams of this spice contains 52 735 IU (1.055% DV) of vitamin A.

Other elaborations that use red pepper as the raw material have similar amounts: cayenne powder provides 41 610 IU per 100 grams.

Yam

It is a food dressed with an orange color which is where the vitamin A is found at 19 200 IU per 100 grams.

Carrot

It contains a milligram per 100 grams, which is the equivalent to 16 700 IU per a hundred grams of raw root.

It is probably the food that has been most socially associated to this vitamin, whose supply comes basically in beta-carotene form.

Rapini

Rapinis are a green, soft, sprouts from turnip (Brassica napus) which are harvested a few days before flowering, and they provide a milligram per 100 grams of their edible part.

Lettuce

Here we must differentiate the kind of lettuce, since its color is related to its richness in vitamin A.

The darker ones have a generous content regarding this aspect, which overcomes 7000 IU in 100 grams, which would mean that the poorest content belongs to the Iceberg lettuce or to the American lettuce with only 5 IU (10% DV)

Sweet potato

A serving of 100 grams contains 650 micro-grams of vitamin A. This makes it a very suitable food for sportspeople and for those who demand high amounts of energy due to its content in carbohydrates.

Tomato

Maybe it is not as rich in vitamin A as it is commonly believed, since it only has 350 micro-grams per 100 grams, but it is so common in our crops and it is so frequently used in our diets, that it represents one of the main nutritional sources of this vitamin.

Melon

A medium slice from a yellow or orange melon supplies two thousand IU of this vitamin (47% DV).

Green leaf vegetables

In general, green leaf vegetables are one of the most favored ingredients due to their nutritional value within a Mediterranean diet, both in salads and steamed (preferably boiled in water). Among them, the one on top of the ranking of vitamin A is green cabbage or kale, with 15 400 IU (308% DV) per 100 grams, followed by mustard leaves (210% DV), spinach (188%), and chard (133% DV).

Pilgrim pumpkin

It is a vegetable of an orange color and with a characteristic sweet nut flavor, a serving of a hundred grams provide 11 150 IU (223% DV) of vitamin A.

Dried herbs

Parsley provides the greatest amount of vitamin A from all of them, a 204% DV in a serving of 100 grams, followed by basil (188% DV), marjoram (161% DV), dill (154% DV), and oregano (138% DV), all of them are used more and more in all kinds of recipes.

Dairy products

  • Butter: a hundred grams provide 800 micro-grams, which reinforces the argument that it is not as harmful as it is usually believed.
  • Cream: a bit less, about 700 micro-grams per 100 grams. The same statement that was used for butter can be applied to this product.
  • Matured cheese: its content varies a little depending on the richness of their fatty matter, but normally they move between 350 micro-grams per 100 grams.

Fish and seafood

Some fish also are a remarkable source of vitamin A, and there is an important association between the shape of their body and their vitamin concentration. This favors those with a long shape such as conger, eel, and salmon (with half a milligram, there is a milligram and thirteen micro-grams per hundred grams respectively), which means that eating a portion allows to cover the daily requirements of this vitamin.

On the other hand, oysters, clams, and cockles have also remarkable amounts but which is still lower than that of the fish, around a micro-gram per gram.

Important biological properties and organic functions of this vitamin

Vitamin A has been granted several functions within the organism and among them, the one that is most popularly known is related to the functioning of the organs that are involved in sight.

However, as we will see now, this is not the only property of a substance that is indispensable for human beings.

The functioning of sight

Let’s make a review of the physiological path that this substance follows once it enters the organism and goes to one of its target organs, the eye.

Ocular Health with Vitamin A

Retinol is driven to the retina, which is the sensitive tissue that is behind the eye. There, it undergoes an oxidation process and it becomes a retinal compound which is channeled to the photoreceptor cells, called rod cells. Inside them, retinol links to opsin, a functional protein. With it, a pigment called rhodopsin is made, which is a complex molecule whose presence in rod cells allows them to detect minimal amounts of light. This feature makes them indispensable for the efficiency of night vision.

An absorbed photon is capable to trigger a chemical reaction of retinal. This produces a domino effect whose result is an electric signal which goes to the optic nerve, one of the twelve pairs of cranial nerves whose mission is to make that signal available to the regulating center of sight in the brain. This allows its interpretation as an image by the brain itself. If there is a retinol deficiency in this sequence of events, the retina will experience a serious impediment in order to see in the dark.

Retinal can also be oxidized to retinoic acid, which ends up linking with certain receptors in order to launch or inhibit the genetic expression. That’s why the chemical form of retinoic acid plays an important role in the regulation of the expression of genetic characters. This is the way to achieve cell specialization in order to carry out very specific physiological tasks.

We cannot finish this section without mentioning the ability of this vitamin to stop a degenerative process that can become a serious burden for sight: macular degeneration related to aging. It produces a loss frontal vision and it is considered one of the main causes of blindness in old people. In order to avoid a fast development of this process, it is recommended to those who detect symptoms of the beginning of a degeneration, to eat a vitamin A supplement with antioxidants, zinc, and copper.

The immune system

The proper functioning of the immune system depends partly on the amount of vitamin A that is available in the organism. Both retinol and the resulting products of its metabolization are essential to maintain the integrity and functionality of the skin and the mucous membranes that cover a great part of the organism (respiratory pathways, digestive tube, urinary conducts…). That ubiquitous tapestry works as a primary defensive wall before external agents that may cause infections. That is why the presence of this vitamin in proper amounts is determinant for its efficiency.

However, the role of vitamin A in the integrity of organic defenses and in the prevention of diseases does not end there. The development and differentiation of the lines of white cells is another physiological process carried out by this vitamin. This is due to the fact that the population of lymphocytes is one of the most determinant cell lines in the mechanism of the immune response.
It is needed for its correct formation both in quantity and quality.

Embryo and fetal development

During pregnancy, a good part of the development of the fetus’ organs depends on the transfer of vitamin A from the mother to the child through the placenta. If there is not a proper supply, it can result in congenital deficiencies for the baby, which in serious situations can even cause premature death. It also participates decisively in the formation of the extremities, heart, eyes, ears, and other organs on a second plane, such as the nerve tissue, the bone matrix, and the immune system.

We can still point to a more subtle intervention of vitamin A, since retinoic acid is linked to mechanisms of the gen that controls the synthesis of somatotropin or the growth hormone.

Consequently, it seems logical that there is a cause-effect relation between vitamin A deficiency in the mother and the baby, and a delay in the growth of the latter.

Formation of red cells

Vitamin A is essential for the proper development of stem cells which are precursors of red cells, called hematopoietic stem cells, in the marrow bone. Moreover, its presence is important in the release of iron from its deposits to the red marrow bone where red blood cells are found in their early development (a red cell needs around two days to be formed). Iron is picked up by an essential component of the hemoglobin molecule, the group heme, which is an irreplaceable and specialized protein in the transport of oxygen to the tissues.

It can be interesting to point out the metabolic interrelations that this vitamin maintain with two of the main minerals, iron and zinc. On the one hand, it is known that a zinc deficiency can cause damage to the transport of retinol, its release in the liver, and its oxidative transformation to retinal. On the other hand, it is known that vitamin A supplementation is efficient in order to fight iron deficiency caused by iron deficiency anemia. This will improve the nutritional state related to this mineral, specially in pregnant women and very young children.

In relation to this, it should be said that it has been proven that a combination of vitamin A and iron supplementation in order to prevent iron deficiency anemia is more efficient than their separated supplementation.

The integrity of the epithelium

Now that we have widely talked about the benefits of Vitamin A for the immune system, here we will focus on the possibilities that this vitamin offers to keep a lustrous skin free from any problems. Basically, it can be pointed out that retinol is essential for the renewal of the layers of epithelial cells and for the repair of the cells that form the mucosa, nails, and hair.

When we talk about this function we cannot help but mention vitamin C, which is indispensable for the formation of collagen, which acts as a connective matrix that supports and reinforces the protection of the body and a fast wound healing process.

Anti-cancerous and anti-aging action

Its antioxidant function can be noticed in two different things:

  • It delays cell aging which is reflected in a better aspect of the person overall.
  • It prevents certain types of cancer since it maintains DNA away from the mutagenic action (which causes changes in its structure) of the harmful agents. 

There are currently several research lines which are trying to deepen in the degree of causality that exists between an elevated consumption of foods with vitamin A and the reduction of the risk of suffering certain types of cancer, more specifically lung and prostate cancer.

Proper development of the nervous system

Here we can talk about a localized intervention on a very specific region of the brain, the hippocampus, which regulates the learning and information processes, and the short-term memory. This is the reason why it seems that vitamin A influences positively the function of neurons that form said region, which encourages a greater facility for mental assimilation and a very sharp memory.

Its excess can also be harmful: hypervitaminosis A

As it has been seen throughout the whole article, vitamin A is an excellent nutrient which is indispensable for our health. However, nature establishes thresholds, more or less strict, for any biologically active substance that enters the organism. This is why it is so important not only to describe the benefits of its intake, but also to warn about the dangers that entails to surpass the thresholds which turn this beneficial substance into a harmful one.

Science calls hypervitaminosis to the intoxication by an excessive consumption of this vitamin. It refers to a deposit of great amounts of vitamin in the organism, which normally happens due to an uncontrolled intake of supplements.

The role of Vitamin A and sport

When it comes to the symptoms that may warn us of an intoxication, we must take into account that they are not constant, but among the most usual ones we can find anorexia, nausea, vomits, blurred vision, hyperexcitability, and other nervous disorders, hepatomegaly (enlarged liver), hair loss, migraines, insomnia, asthenia or muscle weakness, and amenorrhea (interruption of the menstrual cycle. In children it may cause hydrocephalus and cranial hypertension. It can result in a reduction of mineral bone density measured through a densitometry. However, in extreme cases, it can even result in coma and death.

Apart from this, high doses of vitamin A supplements in pregnant women can become a causative factor of congenital anomalies in the offspring: this is the reason why a woman who thinks that she is pregnant should avoid the consumption of high doses.

In order to avoid the risk of suffering hypervitaminosis, it is advisable to know the tolerable upper intake levels which are consolidated as reference data in order to prevent a vitamin A intoxication. Obviously, we should exclude those who are malnourished, those who take periodical supplementation, and those who are under vitamin A treatment in order to combat retinosis pigmentaria or any other pathology whose treatment demands this vitamin in high amounts.

But we must distinguish hypervitaminosis A from hypercarotenemia, which is in fact not considered a pathology and which appears with a yellow color (similar to jaundice) in the palm of the hands due to an accumulation of carotenes. It can be simply caused by eating too many vegetables which contain them abundantly. The color will return to its normal state when this excessive consumption is suppressed.

Intake: How much Vitamin A should we consume, and how

How to manage a proper intake of vitamin A: supplementation

The amount of vitamin A that each person needs must be according to age and the reproductive stage. Generally speaking, it can be said that the recommended intake for those older than 14 moves between 700 and 900 micro-grams daily of a measuring unit known as retinol equivalent (RE). For women who are lactating it increases up to 1200-1300 RE and for children under 15, the numbers descend considerably

The problem is that the conversion from International Units, which is how the vitamin A content figures in the labels of the products, into mcg RE is not an easy task.

In order to illustrate this point, we provide an example of a varied diet of 900 mcg RE of vitamin A which provides between 3000 and 36 000 IU depending on which are the foods that are used.

For people older than 14 years, the FDA (Food and Drug Administration) has fixed a parameter called daily value (DV) of vitamin A of 5000 IU, providing that it is a mixed diet of vegetable and animal origin. DVs do not coincide with recommended intakes, however, if our objective is to reach the 100% of DV of vitamin A, it can be useful in order to ensure a sufficient supply.

However, if the numbers indicated by different institutions are analyzed, we will find certain disagreements. For example, for the Spanish Foundation of the Heart, an entity that can be considered as a reliable source, the daily recommended intake could be represented in the follow scale:

  • 6 to 11 months: 350 micro grams
  • One to 6 years: 400 micro grams
  • 7 to 10 years: 500 micro grams
  • 11 to 14 years: 600 micro grams
  • Women older than 14 years: 600 micro grams
  • Men older than 14 years: 700 micro grams
  • Pregnant and lactating women: 700 micro grams

In the meantime, both the FAO and the World Health Organization (WHO) recommend a consumption of 750 micro-grams of retinol daily for adults. They also recommend to increase this amount in a 50% in lactating mothers and reduce it drastically in children and babies.

Obviously, the individual situations must be taken into account since some people can be suffering from health conditions that can demand additional supplementation. This could be the case of:

  • Premature babies during the first twelve months.
  • Those who suffer from cystic fibrosis in order to recover from the intestinal disorders that it causes.
  • Those who are celiac, since they have difficulties to absorb fat properly.

It should be kept in mind that when it comes to interpreting the numbers that are being provided about the diets, that the model is that of a varied diet with content in retinol and carotenes simultaneously. For example, in the case of a vegan diet, the amount of carotene should be increase because its metabolic transformation in retinol is only partially successful in this kind of diets.

What kinds of vitamin A supplements exist and what are they for?

Like many other substances, vitamin A is abundantly sold as dietary supplements, both in acetate or retinyl palmitate (which is considered preformed vitamin A), or in beta-carotene or pro-vitamin A, or as a combination of both. Most of multivitamin supplements provide vitamin A in their formula and, moreover, there are products whose content is exclusively made of vitamin A. In the online HSN store you can find all these varieties.

However, when it comes to supplementation, it is unavoidable to argue that if we regularly consume proper amounts of fruit and vegetables, and some foods of animal origin such as eggs, long fish, or dairy products (if they are low fat, enriched with vitamin A), supplementation will not be necessary unless there is a pathology that changes the requirements of the organism. Nevertheless, it is known that vitamin A, if consumed following the recommended doses by the manufacturing laboratories, is a substance that is safe.

There are plenty of evidence that endorse the use of vitamin A and its derivatives in order to combat acne.

So, for those young people who suffer from this problem it is recommended that, apart from ensuring that they consume enough vitamin A through their diet, they should add a supplement that includes retinol that can be applied directly on the skin. This is done in order to regulate the layer of fat that is secreted by the sebaceous glands. The result will be a remarkable improvement of the skin.

In this aspect, it is necessary to warn women and to provide some precautions that they should follow if they develop acne. This is because there is a vitamin A variant, called all-trans-retinoic acid or tretinoin (the acid form of this vitamin), which is very efficient in order to combat acne but which can cause congenital malformations in the fetus. A detail that should not go unnoticed about this substance is that it has proven to be successful for the treatment of a severe disease, promyelocytic leukemia, to the point that a significant improvement in its survival has been registered.

Vitamin A supplementation, depending on the case, seems to be a support that should be taken into account for the treatment of malaria, retinosis pigmentaria, HIV, cancer of pancreas, skin, breast, lung, and stomach, arthritis, skin eczema, and diabetes, as well as for the prevention of cataracts.

Those who must not use these supplements in order to not compromise their health are those who suffer from liver diseases and alcoholic people. This is due to the fact that it would increase the risk of suffering a severe intoxication that could have fatal consequences. Those who suffer from a bad absorption syndrome, intestinal infections, or a high rate of triglycerides in blood should also avoid these supplements.

The potential risks of vitamin A in lactating babies have not been proven rigorously. However, since it is an abundant substance in breast milk, its excess could cause congenital alterations, which is the reason why women should avoid these kind of supplements during this period of their lives.

On the other hand, allergy and hypersensitivity to this vitamin have been proven, and those who have been diagnosed with one of them should absolutely avoid its consumption.

Possible interactions with other substances

Oral contraceptives demand precaution when it comes to consuming this vitamin, since they can dangerously increase its levels.

Its combination with some antibiotics should be avoided as well, but specially with tetracyclines, since this mix increases the risk of toxicity. The reason why is because it interacts with these medicines that are metabolized in the liver through the cytochrome P450 enzymatic system.

Be aware of possible hemorrhages when it is combined with acetylsalicylic acid or other anti-coagulants, with non-steroidal anti-inflammatory medicines such as ibuprofen or ginkgo biloba (whose leaves extract is used as a natural remedy for cardiovascular disorders).

All this information can be used to avoid diseases and to promote an ideal health.

Information about recommendations related to this vitamin

  • Vitamin A is stable at normal conservation temperatures and relatively stable to light and heat, although it is destroyed by oxidation.
  • It is not recommended to fry foods that are rich in vitamin A since both carotenes and retinol, which are fat-soluble, will stay in the oil.
  • It is preferable to eat fresh vegetables, since their drying diminishes their carotene concentration.
  • The bioavailability of vitamin A is increased with vitamin E and other natural antioxidant elements.
  • Vegans, who do not consume dairy products nor eggs, need betacarotene in order to meet their vitamin A requirements. In order to do this, it is necessary that they include at least five fruits and vegetables rich in carotenoids in their daily diet.
  • Different vitamin A supplements must not be used simultaneously, since it increases the risk of toxicity.
  • As it happens with any other dietary supplement, even though they are products that do not need medical prescription, it is highly advisable to tell your doctor that you intend to begin supplementation. If you are allowed, they should provide an adequate dose.
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