INTRODUCTION:
Vitamin A and all vitamins are organic substances essential for maintaining many functions physiological and necessary for growth. They were discovered by the Polish biochemist Kazimierz Funk in 1912, who was the first to isolate vitamin B1 from the husk of rice.
The term “vitamin” comes from the Latin vita which means life and from the amine suffix which is the name of a radical in chemistry. Man cannot ensure the synthesis of vitamins in quantity sufficient; they must be brought by food. They are subdivided into two groups: vitamins fat soluble and water soluble vitamins.
Fat-soluble vitamins use the pathways intestinal absorption, transport and excretion of dietary lipids. They include vitamins A, D, E, K. Water soluble vitamins are excreted mainly via the kidney
They include group B vitamins and vitamin C. The recommended nutritional intakes are defined by national expert committees, from data from different studies.
The definition of “Need” includes a step consisting in defining the objectives that the coverage of these needs must allow to achieve. When the clinical signs of a poor nutritional status exist, this already corresponds to a significant impairment.
Vitamin A
Vitamin A is found in foods in two forms: retinol and its esters. Esters of retinol are only found in food of animal origin such as milk, liver, butter, cheese, egg and fish. The term provitamin A is used for all carotenoids which, as soon as they are absorbed, can be converted partially in vitamin A.
The provitamins in form of carotenoids are found in plants: carrots, spinach, green cabbage, sweet potatoes, mangoes, blueberries. Compounds of the vitamin A group undergo the successive actions of secretions gastric and intestinal.
Retinyl esters are hydrolyzed to retinol which is incorporated into chylomicrons and excreted in the lymph. Most of these chylomicrons are taken up by the liver.
Malabsorption of fat can lead to vitamin A deficiency. More than 90% of vitamin A is stored in the liver. The main target tissue for vitamin A is the eye. Retinaldehyde constitutes the prosthetic group of rhodopsin.
This pigment absorbs UV rays and modifies the conformation of rhodopsin, which produces biochemical reactions that result in the transmission of the impulse to the optic nerves.
It is why the first manifestation of a deficiency in vitamin A produces a decrease in visual acuity especially in twilight light. It translates to night blindness, then xerophthalmia and blindness irreversible1.
Vitamin A deficiency concerns mainly developing countries. It is accompanied by a drop in defenses immune systems in certain infectious diseases: diarrhea, measles. Approximately 500,000 children go blind every year and many they die.
In infants, vitamin A requirements are based on the composition of human milk. Current data does not allow to attribute a favorable role to vitamin A in prevention of cancer or disease cardiovascular.
In industrialized countries where the regime food is adequate, we do not recommend vitamin A supplements.
Too much vitamin A can cause nausea, vomiting, dizziness. It can mimic signs of high intracranial pressure. A long term, it can cause ataxia, alopecia, hepatotoxicity.
What are the symptoms of vitamin A deficiency?
1- Dry skin
One of the most important functions of vitamin A is that it helps form skin cells and repair damaged ones, and it also contributes to fighting infections resulting from some skin problems.
This means that low levels of Vitamin A can negatively affect the health of the skin, causing dry skin and an increased risk of many different skin problems, such as eczema.
2- Dryness in the eyes
Dry eyes is one of the most common symptoms of vitamin A deficiency, and unfortunately, in some cases, severe deficiency of this vitamin may cause vision loss or dryness of the cornea of the eye.
It is important that you monitor the health of your eyes constantly, as dry eyes are one of the first symptoms associated with low levels of vitamin A.
3- Night blindness
As mentioned above, vitamin A deficiency negatively affects the eyes, and among these effects is an increased risk of night blindness, as indicated by some recent scientific studies.
In order for a person to see the color spectrum, the eye needs to produce certain pigments in order for the retina to function as required, and the lack of vitamin A levels stops the production of these pigments, which leads to night blindness.
4- Infertility and problems during pregnancy
As we mentioned at the beginning, one of the most important functions of vitamin A is its role in promoting reproductive health for both males and women, in addition to its contribution to supporting the development of fetuses in the womb.
If some couples are having difficulty getting pregnant, it is important that they get their vitamin A levels tested.
Besides, miscarriage may be caused by vitamin A deficiency, so your doctor may ask you to undergo a vitamin A level test in this case.
5- The appearance of various pills on the face
A scientific study published in 2006 found a link between low vitamin A levels and the appearance of acne.
On the other hand, some scientists have suggested that using ointments that contain vitamin A would reduce acne and may help treat it.
6- Delayed growth in children
Children who do not get enough vitamin A may suffer from problems and delays in development, because this vitamin is necessary and important for the proper development of the human body.
What are the risks of vitamin A deficiency in children?
Vitamin A plays an important role in many essential physiological functions in children:
- visual function: retinol is one of the constituents of rhodopsin, a photosensitive protein essential for the function of rods and therefore for adaptation to darkness.
- - trophicity of conjunctival and cutaneous epithelia: vitamin A deficiency leads to an inability of conjunctival goblet cells to produce mucus, which leads to conjunctival and corneal xerosis
- - trophicity of epithelia of the digestive tract and respiratory tract: vitamin A is a major cause of morbidity and mortality in developing countries due to the frequency of gastroenteritis and bronchopneumonia it causes
- - immune defenses: increased sensitivity to viral infections (measles, diarrhea) and pulmonary complications.
Two distinct clinical forms are observed:
- Chronic vitamin A deficiency: It mainly affects children between 3 and 6 years old and is non-blinding. This form is correlated with a low risk of mortality. It is manifested by night blindness, conjunctival xerosis and Bitot's spots.
- These are pathognomonic and correspond to a raised, white and shiny lesion with a foamy appearance on the nasal or temporal bulbar conjunctiva, near the limbus. Bitot's spots do not go away after treatment for vitamin A deficiency
- Acute vitamin A deficiency: this is a chronic deficiency acutely aggravated by infection, diarrhea or intercurrent measles. It mainly affects children between 1 and 4 years old and is potentially blinding.
It is correlated with a high excess mortality. It manifests itself by the occurrence of a corneal ulcer, the risk of superinfection and infectious keratitis of which is high.
This ulceration can progress to keratomalacia (corneal ulcer reaching more than 1/3 of the corneal surface) with a major risk of perforation and corneal necrosis within a few days.
The complications of this disease are the seriousness of the disease with a risk of permanent corneal scar, corneal ectasia or phthyse.
Extra-ocular damage is characterized by:
- cutaneous signs: there is an atrophy of the sebaceous and sweat glands which causes skin dryness and predominantly hyperkeratosis on the outer face of the lower limbs. Alopecia can also be associated with vitamin A deficiency.
- systemic signs: vitamin A deficiency leads to an immune deficiency and in particular a deficit in cellular immunity and a deficit in the secretion of antibodies; it is accompanied by an increase in mortality from infectious pathologies, in particular for respiratory infections, malaria, measles and diarrhea. Stunting is another effect of vitamin A deficiency, described in the animal literature only.
It could induce compressive optic neuropathies secondary to osteopenia with hyperostosis of the orbit bones and narrowing of the optic canal in children.
Symptoms of hypervitaminosis A
Symptoms vary depending on the severity of the condition, and whether it is chronic (Chronic) or acute (Acute), and these are some of the symptoms:
Symptoms of severe hypervitaminosis A:
- Dizziness
- Hypersensitivity.
- Abdominal pain.
- Vomiting
- A feeling of excessive pressure in the brain.
Symptoms of chronic hypervitaminosis A:
- Blurry vision or changes in the sense of vision.
- Bone swelling.
- Bone pain.
- Anorexia.
- Lightheadedness and dizziness.
- vomiting.
- Sensitivity to sunlight.
- Dryness and roughness of the skin.
- Itchy, flaky skin.
- Cracked and broken nails.
- Cracks at the corners of the lips.
- Jaundice
- Hair loss.
- Infections of the airways.
- Confused and confused.
- Mouth sores.
Symptoms of hypervitaminosis A in children:
- Thinning of the skull bones.
- Double vision.
- Inability to gain weight.
- Coma.
- Swelling of the eye ball.
- In pregnant women, an excess of vitamin A may cause birth defects. So if you are pregnant and you have to take an extra dose of a certain vitamin, increase the dose of that vitamin only, and do not double the doses of the general pregnancy vitamins.
- Pregnant women should also completely avoid using skin creams that contain vitamin A, such as retinol cream.