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Vitamin A = Retinol

CAS Number: 68-26-8
PubChem Client ID: 1071
ChemSpider Number: 393012
CHEBI: 17336
ECHA Information Card: 100.031.195

Vitamin A is a nutrient that the body needs in small amounts to function and stay healthy.
Vitamin A helps vision, bone growth, reproduction, growth of epithelium (the cells that line the inner and outer surfaces of the body) and fight infections.
Retinol is fat soluble (soluble in oils and oils).
Vitamin A is found in liver, egg yolk and full-fat dairy products from animals and fish oils.
Retinol can also be made in the body from a substance found in some fruits and vegetables, such as cantaloupe, carrots, spinach, and sweet potatoes.
Vitamin A is being researched in the prevention and treatment of some types of cancer.
Vitamin A is also called Retinol .
Retinol is the fat-soluble vitamin retinol .
Vitamin A binds to and activates retinoid receptors ( RARs ), thereby inducing cell differentiation and apoptosis of some cancer cell types and carcinogenesis . inhibits .
Vitamin A plays an important role in many physiological processes, including the proper functioning of the retina, growth and differentiation of target tissues, proper functioning of the reproductive organs, and modulation of immune function.
Vitamin A is a retinol in which all four exocyclic double bonds have E-(trans-) geometry .
Retinol has a role as a human metabolite , a mouse metabolite , and a plant metabolite .
Retinol is a retinol and a vitamin A.
Vitamin A is a fat-soluble vitamin essential for health, its deficiency can cause vision, skin, bone and immune disorders.
The recommended daily intake for vitamin A is 300 to 700 μg for children and about 700 to 900 μg for adults , these amounts can be achieved through a normal diet.
Higher doses of vitamin A can be toxic and cause a range of signs and symptoms including liver damage, jaundice, enlarged liver and spleen, portal hypertension and cirrhosis.
Vitamin A is a fat-soluble vitamin and an essential nutrient for humans.
Retinol is a group of organic compounds that includes retinol , retinal , retinoic acid, and several provitamin A carotenoids .

Functions of Vitamin A:
Vitamin A has multiple functions:
Retinol is necessary for embryo development and growth, maintenance of the immune system, and vision , where Retinol combines with the protein opsin to form rhodopsin , the light-absorbing molecule necessary for both low light ( scotopic ) and low light ( scotopic ) . vision ) and color vision.
Some carnivorous species lack this enzyme.
Other carotenoids have no vitamin activity.
Retinol , which binds to fatty acids to form retinyl esters , is used to fortify foods and as an oral dietary supplement.
Dietary retinol is absorbed from the digestive tract by passive diffusion, which requires a specific receptor, SCARB1, induced when retinol status is low.
Retinol is stored in lipid droplets in the liver.
high capacity for long-term storage of retinol means that well-nourished people can survive for months on a diet deficient in vitamin A and β- carotene while keeping their blood levels in the normal range.
Only when the liver stores are nearly depleted will the signs and symptoms of deficiency appear.
Retinol is reversibly converted to the retina, then to retinoic acid, which activates hundreds of genes .

Vitamin A deficiency is common in developing countries, particularly in Sub-Saharan Africa and Southeast Asia.
Deficiency can occur at any age, but is most common in preschool-aged children and pregnant women, the latter due to the need to transfer retinol to the fetus.
Vitamin A deficiency is estimated to affect approximately one-third of children under the age of five worldwide, resulting in hundreds of thousands of cases of blindness and death from childhood diseases due to immune system failure.
Reversible night blindness is an early indicator of low vitamin A status.
Plasma retinol is used as a biomarker to confirm vitamin A deficiency .
Breast milk retinol may indicate a deficiency in nursing mothers.
None of these measures indicates the status of liver reserves.
The European Union and various countries have set recommendations for dietary intake and upper limits for safe intake.
toxicity , also called hypervitaminosis A, occurs when too much vitamin A builds up in the body.
This happens only from high-dose dietary supplements, not from the consumption of foods thought to be high in vitamin A.
Symptoms may include nervous system effects, liver abnormalities, fatigue, muscle weakness, bone and skin changes, and others.
both acute and chronic toxicity are reversed after consumption of high-dose supplements is stopped.

What is vitamin A?
There are 2 types of vitamin A.
The first type, known as 'fully formed' vitamin A, is found in meat, poultry, fish and dairy products.
The second type, known as provitamin A, is found in fruits, vegetables, and other plant-based products.
The most common vitamin A precursor found in foods and dietary supplements is beta- carotene .
You need vitamin A for your eyes so you can see properly, especially at night.
Retinol is also important for your immune system and skin.

Uses of Vitamin A:
Vitamin A is also called retinol .
Retinol is one of the 4 fat-soluble vitamins.
This means that it is soluble in fats and oils.
Retinol is found in animal products.
Fat-soluble vitamins are stored in the body.
Precursors of vitamin A are found in plants.
These are called carotenoids .
These are oil soluble but non- toxic even in large quantities .
The best known carotenoid is beta - carotene .
Both retinoids and carotenoids are good antioxidants.
Vitamin A is part of the reproductive process.
Retinol aids sperm growth.
Retinol also helps the baby grow in the womb.
But high doses of vitamin A and synthetic retinols can cause problems with growth in the womb.
Retinol can also cause birth defects.
Vitamin A seems to help growing tissues in an unborn baby.
Retinol also aids in the formation of the placenta during pregnancy.
Vitamin A is an important factor in lifelong growth.
Vitamin A helps the growth and maintenance of epithelial tissues.
These include the mucous membranes, lining of the gastrointestinal tract , lungs, bladder, urinary tract, vagina, cornea, and skin.
Vitamin A also helps the growth of bones and teeth.
Vitamin A prevents the skin from drying out.
This can protect the body from infectious diseases.
Retinol also helps maintain the immune system.
Vitamin A is also necessary for night vision.
Retinol (a metabolite of vitamin A ) combines with opsin (a pigment in the retina of the eye) to form rhodopsin .
This is a chemical that aids night vision.

Medicinal uses of Vitamin A:
Preventing and treating Vitamin A Deficiency
retinols has led governments and nonprofits to promote vitamin A supplementation in foods and create programs that deliver bolus -size oral doses of vitamin A to young children every four to six months.
In 2008, the World Health Organization estimated that vitamin A supplementation in 40 countries prevented 1.25 million deaths from vitamin A deficiency.
All-cause deaths decreased by 24%, and diarrhea and measles cases decreased by 15% and 50%, respectively.

Retinoids :
Tretinoin is all - trans - retinoic acid; first trade name: Retin -A.
Isotretinoin is 13-cis-retinoic acid; first trade name: Accutane .
non-esterified Etretinate and Acitretin , its metabolites , are used orally to treat severe psoriasis.
The retinoic acids tretinoin (all-trans- retinoic acid) and isotretinoin (13-cis-retinoic acid) are prescription topical medications used to treat moderate to severe cystic acne and acne that has not responded to other treatments .
These are usually applied to the face as a skin cream after cleansing to remove make-up and skin oils.
These events are follicular contributes to the normalization of keratinization and the reduction of cohesion of keratinocytes , which leads to follicular occlusion and reduction of microcomedone formation.
retinoid -receptor complex competes for coactivator proteins of AP-1, an important transcription factor involved in inflammation .
Retinoic acid products also reduce sebum secretion from facial pores , which is a food source for bacteria .
topical products that have health claims to reduce facial acne, combat dark spots on the skin, and reduce wrinkles and lines associated with aging often contain retinyl palmitate.
The hypothesis is that it is absorbed and released into free retinol . to be desterified , then converted to retinaldehyde and then to Retinol is metabolized , so Retinol will have the same effects as prescription products with fewer side effects.
esterified Some studies on human skin suggest that retinol is absorbed and then converted to retinol . There is in vivo evidence.

Overview of Vitamin A :
Vitamin A is a fat-soluble vitamin.
Different forms of retinols are often referred to as " retinoids ".
retinol , retinal , retinoic acid and retinyl ester.
Vitamin A is essential for the proper growth and functioning of many parts of the body, including the eyes, skin, and immune system.
Retinol can be found in many foods, including fruits, vegetables, and fish.
Carotenoids are a group of chemicals found in plants.
Some can be converted into vitamin A in the body.
People most often use vitamin A to treat vitamin A deficiency.
Retinol is also used for aging skin, acne, HIV/AIDS, cataracts, child development, infections and many other conditions.
Vitamin A is the general name of a group of fat-soluble compounds that are extremely important for human health.
is essential for many processes in your body, including ensuring the normal functioning of your system and organs and helping unborn babies grow and develop properly.
men take 900 mcg of retinol , women 700 mcg , and children and adolescents 300-600 mcg of vitamin A per day.
Vitamin A compounds are found in both animal and plant foods and come in two different forms: preformed vitamin A and provitamin A.
Preformed vitamin A is known as the active form of the vitamin that your body can use as it is.
Retinol is found in animal products, including meat, chicken, fish, and dairy products, and contains the compounds retinol , retinal , and retinoic acid.
provitamin A carotenoids - alpha - carotene , beta - carotene and beta - cryptoxanthin - are the inactive form of the vitamin found in plants.
Retinol is converted to the active form in your body.
For example, beta - carotene is converted to retinol (an active form of vitamin A) in your small intestine .

Vitamin A:
Vitamin A is a fat-soluble vitamin that has antioxidants and is found in fruits, vegetables, meat and dairy products.
Retinol improves vision, supports the immune system and helps organs work. The intake of this vitamin varies by age group.
Retinol fights against free radical formation that causes aging and deadly diseases such as cancer.
Retinol and carotenoids are two substances found in vitamin A.

Nutritional Value of Vitamin A:
According to RDA recommendations, the recommended dose is 700 for women and 900 for men. Orange fruits and vegetables contain high amounts of this vitamin.
Retinol has a compound called beta- carotene , which is found largely in carrots, sweet potatoes, and squash . Leafy greens like kale, spinach, and broccoli also contain high amounts.
Because the vitamins are oil-based, the body can absorb them much more efficiently.
Animal fats contain more fat, so you can regulate the amount of fat to preserve its nutritional value by cooking in olive oil or simply baking.

Vitamin A:
Vitamin A is a fat-soluble vitamin that is stored in the liver.
There are two types of vitamin A found in the diet.
Preformed vitamin A is found in animal products such as meat, fish, poultry, and dairy products.
provitamin A, are found in plant-based foods such as fruits and vegetables.
The most common type of pro -vitamin A is beta- carotene .
Vitamin A is also found in dietary supplements.
Retinol often comes in the form of retinyl acetate or retinyl palmitate (preformed vitamin A), beta- carotene ( provitamin A), or a combination of preformed and provitamin A.

Functions of Vitamin A:
Vitamin A helps form and maintain healthy teeth, skeletal and soft tissues, mucous membranes and skin.
Retinol is also known as retinol as it produces pigments in the retina of the eye .
Vitamin A supports good vision, especially in low light.
Retinol also has a role in healthy pregnancy and breastfeeding.

Vitamin A is found in foods in two forms:
Retinol : Preformed retinol is an active form of vitamin A. It is found in animal liver, whole milk, and some fortified foods.
Provitamin A carotenoids : Carotenoids are plant pigments (dyes). When ingested, the body converts these compounds into vitamin A.
more than 500 known carotenoids .
One such carotenoid is beta - carotene .
Beta - carotene is an antioxidant.
Antioxidants protect cells from damage caused by substances called free radicals.

Functions of free radicals :
It contributes to some long-term diseases.
play a role in aging
Eating food sources containing beta- carotene may reduce the risk of cancer.

Metabolic functions of Vitamin A :
metabolic functions of vitamin A are mediated by all - trans - retinoic acid (RA).
RA formation from the retina is irreversible. It must be oxidized and eliminated to prevent the accumulation of RA.
Three cytochromes catalyze the oxidation of retinoic acid .

Vision and eye health:
Vitamin A status involves eye health through two distinct functions.
The retina is an important factor in rod cells and cone cells in the retina that respond to light exposure by sending nerve signals to the brain.
An early symptom of vitamin A deficiency is night blindness.
Vitamin A in the form of retinoic acid is essential for normal epithelial cell functions.
Severe vitamin A deficiency common in infants and young children in Southeast Asia, conjunctival It causes xerophthalmia characterized by dryness of the epithelium and cornea .
Untreated, xerophthalmia progresses to corneal ulceration and blindness.

The role of vitamin A in the visual cycle is particularly relevant to the retinal compound.
Retinol is converted to 11-cis-retinal by the enzyme RPE65 in the retinal pigment epithelium .
In the eye, 11-cis-retinal binds to opsin protein to form rhodopsin in rod cells and iodopsin in cone cells .
When light enters the eye, it isomerizes to the 11-cis-retinal all - trans form .
All - trans retinal degrades from opsin in a series of steps called photobleaching .
This isomerization induces a nerve signal that travels along the optic nerve to the visual center of the brain.
After cleavage from opsin , all - trans - retinal is recycled and converted back to the 11-cis-retinal form through a series of enzymatic reactions, and then binds to opsin to regenerate rhodopsin in the retina, completing the cycle.
addition, some of the all - trans retinal can be converted to the all - trans form of retinol and then converted into an interphotoreceptor. It can be transported to retinal pigmented epithelial cells by retinol -binding protein .
Further esterification to all - trans retinyl esters allows storage of all - trans - retinol within the pigment epithelial cells for reuse as needed .
Retinolt therefore causes rhodopsin deficiency in vitamin A. It will prevent its reformation and lead to one of the first symptoms, night blindness.

Night blindness:
Vitamin A deficiency, which causes night blindness, is a reversible difficulty for the eyes to adapt to dim light.
is common in young children who are malnourished in terms of retinol and beta - carotene .
A process called dark adaptation typically causes an increase in photopigment amounts in response to low lighting levels.
This increases light sensitivity by up to 100,000 times compared to normal daylight conditions.
A significant improvement in night vision occurs within ten minutes, but it may take up to two hours for the process to reach maximum effect.
People expecting to work in a dark environment would wear red-tinted glasses or be in a red-light environment to avoid reversing adaptation, because red light does not deplete rhodopsin compared to what occurs in yellow or green light.

Xerophthalmia caused by severe vitamin A deficiency , conjunctival characterized by pathological dryness of the epithelium and cornea.
The conjunctiva becomes dry, thick and wrinkled.
The indicator is the appearance of Bitot spots , which are clusters of keratin residues deposited within the conjunctiva .
If left untreated, xerophthalmia can lead to dry eye syndrome, corneal ulceration , and eventually blindness as a result of corneal and retinal damage.
Southeast Asia, estimates are that more than half of children under the age of six have subclinical vitamin A deficiency and night blindness, and the leading cause of preventable childhood blindness progresses to xerophthalmia .
Estimates are that there are 350,000 cases of childhood blindness due to vitamin A deficiency each year.
Causes are vitamin A deficiency during pregnancy, followed by low vitamin A transfer during lactation, and infant/child diets low in vitamin A or beta- carotene .
prevalence of preschool-aged children blinded by vitamin A deficiency is lower than would be expected from the incidence of new cases, because childhood vitamin A deficiency significantly increases all-cause mortality.

In vertebrates and invertebrate chordates , RA has a very important role during development.
levels of endogenous RA signaling during both very low and very high early embryology , congenital lead to birth defects, including vascular and cardiovascular defects.
Fetal Alcohol Spectrum Disorder encompasses congenital anomalies , including craniofacial , auditory, and ocular defects , neurobehavioral abnormalities, and intellectual disabilities caused by maternal alcohol consumption during pregnancy .
that there is competition between acetaldehyde , an ethanol metabolite , and retinaldehyde ( retinal ) for aldehyde dehydrogenase activity in the embryo, leading to a retinoic acid deficiency and attributing congenital birth defects to the loss of RA-activated gene activation.
In support of this theory, developmental defects caused by ethanol can be improved by increasing retinol or retinal levels.
too much Retinol , prescription medications such as tretinoin (all trans - retinoic acid) and isotretinoin (13-cis-retinoic acid) , used orally or topically to treat acne, contain warnings not to be used by pregnant women.

Immune function:
Historically, vitamin A deficiency (VAD) has been associated with compromising resistance to infectious diseases.
VAD is common in early childhood , vitamin A supplementation plays a role in the immune system's proliferation and differentiation of white blood cells, directing T cells to the intestinal tract, and up- and down-regulation of lymphocytes.
Lymphocytes and monocytes are types of white blood cells of the immune system.
Lymphocytes include natural killer cells that function in innate immunity, T cells for adaptive cellular immunity, and B cells for antibody-driven adaptive humoral immunity.
Monocytes differentiate into macrophages and dendritic cells.
Both types of white blood cells are created in the bone marrow, then pass into the bloodstream. RA triggering of receptors in the bone marrow is essential for hematopoiesis .
migrate to the thymus , where they differentiate into various types of T cells, in some cases called "killer" or "helper" T cells, and further differentiate after leaving the thymus .
Each subtype has functions that are directed by the types of cytokines secreted and organs to which cells preferentially migrate, also described as trafficking or target-seeking.
Retinol promotes T helper cell differentiation.
retinol is sufficient, the Th1 subtype is suppressed and Th2, Th17 and Treg (for the regulator) are stimulated.
down-regulation of immune activity seen as tolerance of self-non-food proteins and tolerance of bacteria and other organisms residing in the microbiome of the large intestine.
retinol is not sufficient, the results are pro- inflammatory and can contribute to allergic reactions and autoimmune activity, where the immune system responds to the host's cells.

mesenteric lymph node cells collected from vitamin A-deficient animals in the early 1980s and subsequently radio-isotope-labeled to accumulate in the intestinal tract of vitamin A-sufficient recipients.
More recent animal research has shown that dendritic cells found in intestinal tissue have enzymes that convert the retina to all - trans retinoic acid for uptake by retinoic acid receptors on lymphocytes .
triggers gene expression leading to T cell types Th2, Th17, and iTreg , and migrate to and reside in mesenteric lymph nodes and Peyer 's patches in the outer and inner wall of the small intestine, respectively.
Dendritic cells also contribute to innate immunity.
In the case of vitamin A deficiency, innate immunity is compromised, there is no RA signaling and proinflammatory Th1 cells predominate.

Vitamin A deficiencies have been associated with increased susceptibility to skin infection and inflammation.
appears to modulate the innate immune response and maintain the homeostasis of epithelial tissues and mucosa through its metabolite .
As part of the innate immune system, toll-like receptors on skin cells respond to pathogens and cell damage by inducing a pro-inflammatory immune response that includes increased RA production.
epithelium of the skin encounters bacteria, fungi and viruses. Keratinocytes of the epidermal layer of the skin , antimicrobial produces and secretes peptides ( AMPs ).
AMPs Production of resistin and cathelicidin is promoted by RA.
A healthy skin and hair follicle , especially on the face of vitamin A Another way it helps maintain its microbiome is by reducing sebum secretion, which is a food source for bacteria.

Use of Vitamin A:
Retinol is used in dietary supplements and skin care.

Dietary supplement:
Retinol is sometimes used as a dietary supplement to treat or make up for vitamin A deficiency.
Vitamin A deficiency can cause night blindness and xerophthalmia (irreversible damage to the cornea), and retinol supplementation is used to treat and prevent these conditions.
Sometimes Retinol is in the form of oral medications in the form of tablets or capsules.
Other times, retinol is injected directly into the muscles so that it can be quickly absorbed into the bloodstream.

Skin care:
Retinol has many functions in skin care and cosmetic products.
First, Retinol is an anti-aging ingredient.
applied topically , Retinol helps reduce wrinkles, treat hyperpigmentation and generally reduce the signs of skin aging.
Retinol is also used to treat acne and acne scars.
Most over-the-counter acne-fighting creams and gels have retinol as the active ingredient .
hyperpigmentation , tissue and psoriasis often add this to their formulations .
retinol works in the skin changes the way cells in the dermis and epidermis work.
More specifically, Retinol increases the rate at which these cells divide to form new cells.

is a general term that refers to fat-soluble compounds found as preformed vitamin A ( retinol ) in animal products and provitamin A carotenoids in fruits and vegetables .
The three active forms of vitamin A in the body are retinol , retinal , and retinoic acid.
Vitamin A plays a role in regulating the growth and specialization (differentiation) of almost all cells in the human body.
Vitamin A has important roles in embryonic development, organ formation during fetal development, normal immune functions, eye development and vision.
Vitamin A deficiency is a major cause of preventable blindness worldwide. It is most common in children and women of childbearing age.
Vitamin A deficiency is associated with increased susceptibility to infections, as well as thyroid and skin disorders.
Vitamin A prophylaxis appears to significantly reduce childhood deaths in areas with a high risk of vitamin A deficiency.
high-dose vitamin A supplementation is commonly recommended for children over six months of age who are malnourished, immunocompromised, or at risk for measles complications .
Retinoic acid and its analogs are used in pharmacological doses in the treatment of acute promyelocytic leukemia and various skin diseases.
Animal food sources rich in preformed vitamin A include dairy products, fortified cereal, liver and fish oils.
Rich sources of provitamin A carotenoids include orange and green vegetables such as sweet potatoes and spinach.
Excess consumption of preformed vitamin A can be highly toxic and is particularly contraindicated before and during pregnancy, as it can cause serious birth defects .
tolerable upper intake level (UL) for vitamin A in adults is 3,000 μg RAE/day.
UL does not apply to vitamin A derived from carotenoids .
Vitamin A is a general term that encompasses a number of related compounds.
Retinol and retinyl esters are often referred to as preformed vitamin A.
Retinol can be converted by the body into retinal, which in turn can be oxidized to retinoic acid , a form of vitamin A known to regulate gene transcription .
Retinol , retinal , retinoic acid, and related compounds are known as retinoids . β - carotene and other food carotenoids that can be converted to retinol by the body are called provitamin A carotenoids .
Hundreds of different carotenoids are synthesized by plants, but only 10% of them can be converted to retinol .
focus on preformed vitamin A compounds and retinoic acid.

Computed Proporties of Vitamin A:    
Molecular Weight: 286.5    
XLogP3: 5.7    
Hydrogen Bond Donors : 1    
Number of Hydrogen Bond Acceptors: 1    
Number of Rotatable Ties: 5    
Full Mass: 286.229665576    
Monoisotopic Mass: 286.229665576    
Topological Polar Surface Area: 20.2 Å ²    
Heavy Atom Count: 21    
Net Load: 0    
Complexity: 496    
Isotope Atomic Number: 0    
Atom Stereocenters Defined : 0    
Undefined Atom Stereocenter Count: 0    
Defined Number of Bond Stereocenters : 4    
Undefined Bond Stereocenters : 0    
Covalently Bonded Units: 1    
Compound Canonicalized : Yes    

Chemical and physical data of Vitamin A:
formula : C20H30O
Molar mass: 286.4516 g mol−1
Melting point: 62–64 °C (144–147 °F)
Boiling point: 137–138 °C (279–280 °F) (10−6 mm Hg)
Molecular Weight: 286.5

Absorption, metabolism and excretion of Vitamin A:
derived from foods of animal origin or synthesized for dietary supplements are activated by retinyl ester hydrolases in the lumen of the small intestine to release free retinol .
Retinol enters intestinal absorbent cells by passive diffusion.
The absorption efficiency is in the range of 70% to 90%.
Inside the cell , retinol is bound to retinol -binding protein 2 (RBP2).
Retinol then lecithin retinol It is enzymatically re- esterified by the action of acyltransferase and incorporated into chylomicrons secreted into the lymphatic system .
Unlike retinol , β- carotene It is taken up by the membrane carrier protein scavenger receptor B1 (SCARB1) by enterocytes .
-regulated during times of vitamin A deficiency .
If vitamin A status is in the normal range, SCARB1 is down -regulated , reducing absorption.
the enzyme BC01, which is responsible for the symmetrical cleavage of β - carotene into the retina, is also downregulated .
Absorbed β - carotene is then either incorporated as is into chylomicrons or converted first to retinal and then to retinol and bound to RBP2 .
After a meal, roughly two-thirds of the chylomicrons are taken up by the liver and the rest is delivered to peripheral tissues.
Peripheral tissues, chylomicron β - carotene It has the capacity to convert to retinol .

retinol in the liver means that well-nourished people can live for months on a vitamin A-deficient diet without showing signs and symptoms of deficiency.
Two liver cell types are responsible for storage and release: hepatocytes and hepatic stellate cells ( HSCs ).
hepatocytes take up lipid -rich chylomicrons , retinol It binds to retinol -binding protein 4 (RBP4) and transfers retinol-RBP4 to HSCs for storage in lipid droplets as retinyl esters .
Mobilization reverses the process: retinyl ester hydrolase releases free retinol , which is transferred to hypatocytes , binds to RBP4, and enters the bloodstream .
retinol is bound to RBP4 , except that it exceeds the liver's storage capacity after a meal or when consumed in large quantities .

Carnivores manage vitamin A differently.
Carnivores are more tolerant of high retinol intakes through their ability to excrete retinol and retinyl esters in the urine.
Carnivores, liver HSCs compared to omnivores and herbivores Due to its higher ratio to hepatocytes , it has more storage capacity in the liver.
For humans, the liver content can range from 20-30 μg /gram wet weight.
Notably, polar bear liver is acutely toxic to humans, as the content has been reported to be in the range of 2,215 to 10,400 µg /g wet weight.
As noted, in humans, retinol circulates bound to RBP4. Carnivores keep R-RBP4 in a narrow range while also having retinyl esters in circulation.
Esters are excreted in the urine, while bound retinol is delivered to the cells.
In general, carnivorous species are poor converters of ionone -containing carotenoids , and pure carnivores such as felines (cats) completely lack the cleavage enzyme.
They must have already formed vitamin A in their diet.
In the liver and peripheral tissues, retinol is reversibly converted to retinal by the action of alcohol dehydrogenases , which are also responsible for the conversion of ethanol to acetaldehyde .
The retina is irreversibly oxidized to retinoic acid (RA) by the action of aldehyde dehydrogenases .
of RA oxidative degradation is induced by RA – its presence triggers its removal, creating a short-acting gene transcription signal.

Vitamin A Deficiency:
Vitamin A deficiency is rare in the United States. However, vitamin A deficiency is common in many developing countries because residents often have limited access to foods containing preformed vitamin A from animal-based food sources and do not commonly consume available beta- carotene -containing foods due to poverty.
According to the World Health Organization, 190 million preschool-aged children and 19.1 million pregnant women worldwide have a serum retinol concentration of less than 0.70 micromol /L.
In these countries, low vitamin A intake is most strongly associated with health outcomes during periods of high nutritional demand, such as infancy, childhood, pregnancy and breastfeeding.

In developing countries, vitamin A deficiency typically begins in infancy when babies are not getting enough colostrum or breast milk.
Chronic diarrhea also leads to excessive loss of vitamin A in young children, and vitamin A deficiency increases the risk of diarrhea.
The most common symptom of vitamin A deficiency in young children and pregnant women is xerophthalmia .
xerophthalmia is night blindness or the inability to see in low light or darkness.
Vitamin A deficiency is one of the most important causes of preventable blindness in children.
People with vitamin A deficiency (and often xerophthalmia with characteristic Bitot spots ) tend to have a low iron status, which can cause anemia.
Vitamin A deficiency also increases the severity of infections (especially diarrhea and measles) and the risk of death, even before the onset of xerophthalmia .

Food Sources of Vitamin A:
Many cereals, juices, dairy products, and other foods are fortified with retinol (preformed vitamin A).
Many fruits and vegetables and some supplements contain beta- carotene , lycopene , lutein or zeaxanthin .
Green leafy vegetables (cabbage, spinach, broccoli), orange and yellow vegetables (carrots, sweet potatoes, pumpkin and other winter squash, summer squash)
red bell pepper
melon , mango
beef liver
fish oils
Fortified foods

Symptoms of Vitamin A Deficiency and Toxicity :
Vitamin A deficiency is rare in Western countries, but it can occur.
Conditions that interfere with normal digestion, celiac disease, Crohn's disease, cirrhosis, alcoholism, and cystic It can lead to vitamin A malabsorption, such as fibrosis .
Mild vitamin A deficiency can cause fatigue, susceptibility to infections, and infertility.
The following are symptoms of a more serious deficiency.
Xerophthalmia , severe dry eye that can lead to blindness if left untreated
nictalopia or night blindness
Irregular patches on the white of the eyes
dry skin or hair

Why do people take vitamin A?
Topical and oral retinoids are common prescription treatments for acne and other skin conditions, including wrinkles.
Oral vitamin A is also used as a treatment for measles and dry eye in people with low vitamin A levels. Vitamin A is also used for a certain type of leukemia.
Vitamin A has been studied as a treatment for cancers, cataracts, and many other conditions, including HIV. However, the results are not conclusive.
Most people get enough vitamin A from their diet.
However, a doctor may recommend vitamin A supplements to people with vitamin A deficiency.
The people most likely to have a vitamin A deficiency are those with illnesses (such as digestive disorders) or a very poor diet.

What is Vitamin A?
Vitamin A is actually a group of antioxidant compounds that play an important role in vision, bone growth and the health of the immune system.
Vitamin A also helps the surface of the eyes, mucous membranes and skin to be effective barriers against bacteria and viruses, reducing the risk of eye infections, respiratory problems and other infectious diseases.
In general, there are two types of vitamin A, depending on the type of food source it comes from:
Sweet potatoes and carrots are excellent sources of provitamin A carotenoids that are good for your eyes .
Vitamin A taken from foods of animal origin is called retinol .
This "preformed" vitamin A can be used directly by the body.
retinol vitamin A include beef and chicken liver, whole milk and cheese.
Vitamin A, obtained from colorful fruits and vegetables, is in the form of " provitamin A" carotenoids , which are converted into retinol by the body after ingestion of nutrients.
provitamin A carotenoids include carrots, sweet potatoes, spinach, kale and cantaloupe.
Beta - carotene is one of the most common and effective provitamin A carotenoids .

Eye Benefits of Vitamin A and Beta -Carotene :
Retinol is essential for good vision , as vitamin A helps protect the surface of the eye (cornea) .
Studies show that vitamin A eye drops are effective in treating dry eyes.
In fact, one study found that over-the-counter eye drops containing vitamin A were as effective at treating dry eye syndrome as more expensive prescription eye drops formulated to treat dry eye.
Vitamin A eye drops, superior limbic It has also been shown to be effective in treating a certain type of eye inflammation called keratoconjunctivitis .
Vitamin A appears to play a role in reducing the risk of vision loss from macular degeneration (AMD), at least when used in combination with other antioxidant vitamins.
Retinol is also a combination of vitamin A and lutein , retinitis appears to be able to prolong the duration of vision in people suffering from pigmentosa (RP) .
A four-year study led by researchers from Harvard Medical School and other leading universities found retinitis taking a daily supplement of vitamin A and lutein (12 mg). found that pigmentosa patients had slower peripheral vision loss than those who did not receive the combined. supplements .
beta-carotene is converted to vitamin A in the body, this provitamin A of Retinol is likely to provide similar eye benefits as preformed retinol - type vitamin A, but more research is needed to confirm this.

Vitamin A Benefits:
Vitamin A contributes to various bodily functions and helps prevent a number of problems, including:
night blindness
infections , especially in the throat, chest, and abdomen
follicular , which can lead to dry , bumpy skin hyperkeratosis
fertility issues
delayed growth in children

Acne, psoriasis and other skin disorders:
retinoids , a synthetic form of vitamin A , are used to help clear up severe acne and psoriasis.
Retinol also shows promise in treating other skin disorders, warts, and premature aging from the sun.
Recent research shows that topical forms, along with antioxidants, can help minimize the appearance of fine lines and wrinkles.
Retinol requires close supervision by a doctor.
Isotretinoin ( Accutane ), an oral medication for acne , can cause very serious side effects and should not be used by pregnant women or women of childbearing age who are not taking birth control.

Eye disorders:
Getting enough vitamin A in your diet is essential for good vision.
Studies show that people who consume more foods containing vitamin A are less likely to develop age-related macular degeneration.
Additionally, a large population study found that people who took high levels of vitamin A despite their diet had a lower risk of developing cataracts.
But researchers don't know if taking vitamin A supplements would work the same way.
Vitamin A supplements cause retinitis , an inherited disease that causes poor night vision It can help slow down the damage from pigmentosa a little bit.

For children with vitamin A deficiency, supplements can reduce the severity and complications of measles.
Children with a vitamin A deficiency are more likely to develop infections, including measles.
In regions of the world where vitamin A deficiency is common or where at least 1% of measles patients die, the World Health Organization (WHO) recommends that children with measles be supplemented with vitamin A.
However, vitamin A doesn't seem to help unless a child has a vitamin A deficiency. Never give a child a vitamin A supplement without a doctor's supervision.

Inflammatory bowel disease:
IBD who have ulcerative colitis or Crohn's disease may have trouble absorbing all the nutrients their bodies need.
Doctors often recommend that people with IBD take a multivitamin , including vitamin A.

It is not clear whether vitamin A can reduce the risk of cancer.
People who eat a healthy diet with adequate beta - carotene and other carotenoids from fruits and vegetables appear to have a lower risk of certain cancers, such as:
breast cancer
Colon cancer
Esophageal cancer
cervical cancer

Some laboratory studies suggest that vitamin A and carotenoids may help fight certain types of cancer in test tubes.
Several studies have shown that taking vitamin A supplements will help prevent or treat cancer. In fact, there is some evidence that it can be harmful.
Taking beta- carotene or vitamin A supplements has been associated with a higher risk of lung cancer in people who smoke or drink alcohol.
But some researchers say more work is needed to confirm this.
A preliminary study found that a topical form of vitamin A This suggests that it may reduce the abnormal growth of cells on the cervix , called neoplasia .
retinoids , a synthetic form of vitamin A, for skin cancer .
People with certain types of skin cancer tend to have lower blood levels of vitamin A and beta- carotene .

Before taking vitamin A:
It's important to talk to your doctor or pharmacist before you start taking vitamin A to make sure this is the right treatment for you:
If you are pregnant, trying to have a baby or breastfeeding. This is because you should not take vitamin A supplements during pregnancy or if you are breastfeeding unless prescribed by a doctor.
if you have ever had an allergic reaction to a medicine.
If you are taking other medicines, including herbal and complementary medicines, as well as those that can be purchased without a prescription.
is especially important to tell if you are taking a retinoid preparation ( such as isotretinoin ) for a skin condition .

How to take vitamin A?
Before you start taking a vitamin A supplement, please read the manufacturer's printed information leaflet from inside the pack.
Vitamin supplements are usually taken once a day. Your doctor, pharmacist or health visitor will tell you how much you (or your child) should take.
The dose will also be on the label of the pack. You can take vitamin supplements at whatever time of day you find the easiest to remember.
Retinol can be taken before or after meals.
Do not take more than the recommended or prescribed dose.

Vitamin A Deficiency:
Vitamin A deficiency is the leading cause of preventable childhood blindness and increases the risk of death from common childhood diseases such as diarrhea.
Periodic, high-dose vitamin A supplementation is a low-cost intervention proven to reduce all-cause mortality by 12 to 24 percent and is therefore an important program to support efforts to reduce child mortality.
The World Health Organization classified vitamin A deficiency as a public health problem affecting approximately one-third of children aged 6 to 59 months in 2013, with the highest rates in Sub-Saharan Africa (48 percent) and South Asia (44 percent) . .
Only 11 countries achieved two-dose coverage of 80 percent or more in 2020.
Future efforts will need to focus on strengthening systems so that more children can be protected.

Vitamin A is a fat-soluble vitamin that helps maintain normal reproduction, vision and immune function.
The term vitamin A is used in the context of dietary requirements to include provitamin A carotenoids , which are dietary precursors of retinol .
carotenoids in nature have provitamin A activity, but food composition data are available only for α - carotene , ß- carotene , and ß- cryptoxanthin .
Preformed vitamin A is only found in foods of animal origin, while dietary carotenoids are mainly found in oils, fruits, and vegetables.
Vitamin A intakes or requirements are often expressed in terms of retinol equivalents (RE).
One RE, 1 µg It is defined as the biological activity associated with all - trans retinol .
Although there is some ongoing debate in the literature about the conversion rates of carotenes, 6 µg all - trans ß- carotene and 12 µg α- carotene , ß- cryptoxanthin , and other provitamin A carotenoids have been retained as equivalent conversion figures. to 1 RE .
carotene sources in the Australian and New Zealand diets .
FAO:WHO 2001) , which concluded that the literature to date is insufficient to justify a change in conversion rates .

Functions of Vitamin A:
eyes, the retina combines with a protein called opsin to give rhodopsin , an essential light-absorbing molecule necessary for color vision and dim-light vision .
Retinoic acid, another form of vitamin A , is a hormone-like growth factor for epithelial cells and other cell types in the body.

Sources of vitamin A:
Vitamin A is found in both plant and animal food sources. The form of vitamin A that is absorbed when animal sources are consumed is retinyl palmitate , which is converted to an alcohol called retinol .
Retinol acts as a storage form of vitamin A, which can be converted to retinal and from it, the active aldehyde form of the molecule.
One of the richest animal sources of vitamin A is liver.
Plant sources of vitamin A include orange and yellow fruits and vegetables such as carrots, pumpkins, sweet potatoes, apricots and mangoes.
The orange/yellow pigment is formed due to the presence of provitamin A carotenoids such as beta- carotene .
These compounds must be converted to vitamin A or retinol in the body before they can be used .
The daily amount of vitamin A required by adults is 0.7 mg for men and 0.6 mg for women.
Any vitamin A that is not needed immediately is stored for future use in bodily functions.

What does vitamin A do?
Vitamin A has a number of important functions. For example he:
skin and mucous linings (e.g. in the nose)
Helps strengthen immunity against infections
Helps to see in dim light
What happens if I take too much?

Some research suggests that taking an average of more than 1.5 mg of vitamin A per day for many years can affect your bones and increase the likelihood of fractures as you age.
Older people, especially women, are already at risk for osteoporosis. This is where bone density decreases and therefore the risk of fractures increases.
If you eat liver or liver paste once a week, you may be getting more than 1.5 mg of vitamin A per day, on average.
If you're not getting enough vitamin D, you may be more at risk for the harmful effects of too much vitamin A.
People who may be particularly deficient in vitamin D include Asian women who always cover their skin when outside, and older people who rarely go outside.
Therefore, if you are deficient in this vitamin, it may be a good idea to increase the amount of vitamin D you take.
Good sources of vitamin D include fatty fish and eggs.
The best source of vitamin D is summer sunlight, but remember, be careful not to get burned if you're in the sun.
Many multivitamins contain vitamin A.
Other supplements, such as fish liver oil, are also high in vitamin A.
Therefore, if you are taking supplements containing vitamin A, make sure you do not get more than 1.5 mg total per day from your food and supplements.
If you eat liver every week, you should avoid taking supplements containing vitamin A.
If you are pregnant, taking large amounts of vitamin A can harm your unborn baby.
Therefore, if you are pregnant or considering having a baby, you should avoid consuming liver products such as liver or pate because they are very high in vitamin A.
You should also avoid taking supplements containing vitamin A.
Ask your doctor or midwife for more information.

Why do you need vitamin A during pregnancy?
Vitamin A is a fat-soluble vitamin that is stored in the liver. Vitamin A is important for your baby's embryonic growth , including the development of the heart, lungs, kidneys, eyes and bones, as well as the circulatory, respiratory and central nervous systems .
Vitamin A is especially important for women who are about to give birth, as it aids in tissue repair after childbirth.
It also helps maintain normal vision, fights infections, supports your immune system and aids in fat metabolism.
There are two forms of vitamin A: preformed vitamin A and provitamin A carotenoids .
Preformed vitamin A ( also known as retinol ) is used directly by the body and is found in animal products such as eggs, milk, and liver.
Provitamin A carotenoids (like beta - carotene ) are found in fruits and vegetables, and your body needs to convert this type to retinol .

What are the functions of vitamin A?
Vitamin A plays a key role in enhancing and supporting our vision, keeping our immune system working properly, and helping our cells and tissues grow and develop.
Vitamin A is particularly important for reproduction, as it helps the normal growth and development of the embryo.

What Are the Signs of a Deficiency?
Vitamin A deficiency is common in developing countries, but is extremely rare in the United States.
One of the earliest signs of deficiency is night blindness. Permanent blindness can occur if the deficiency is not controlled.
Vitamin A deficiency also causes opportunistic infectious diseases such as measles and pneumonia to be fatal.
Alcoholics can develop vitamin A deficiencies and as a result must include rich sources of vitamin A in their diet (while simultaneously reducing or eliminating their alcohol consumption sharply).
However, supplements may not be wise for alcoholics because vitamin A is stored in the liver and existing liver damage can make them more susceptible to vitamin A toxicity .
In such cases, the supervision of a doctor is very important.

What is vitamin A?
Vitamin A is found in milk, cheese, eggs, butter, fortified margarine, meat, liver, fatty saltwater fish, grains, oils, carrots, zucchini, dark green and yellow vegetables, and fruits such as cantaloupe or apricots.
Vitamin A is important for eyes and skin, the immune system, and normal growth.
Vitamin A is a fat-soluble vitamin that is absorbed along with the fats in your diet and stored in your body's fatty tissue.
Vitamin A is used to treat vitamin A deficiency.
Vitamin A is likely to prevent cataracts or retinitis . It is effective in slowing the progression of pigmentosa (an eye disease that damages the retina).
Vitamin A is also effective in preventing diarrhea in malnourished pregnant women.
Vitamin A may also be used for purposes not listed in this medication guide.
Benefits of Vitamin A Vitamin A helps vital organs such as the heart, kidneys and lungs function optimally.

This antibiotic can reduce the body's ability to absorb vitamin A, especially when taken in high doses.

Omeprazole :
Omeprazole ( gastroesophageal reflux disease or "heartburn") may affect the absorption and effectiveness of beta- carotene supplements.
this drug affects the absorption of beta- carotene from food.

Retinoids :
These drugs are a synthetic form of vitamin A and are sometimes prescribed in high doses.
retinoids should not take additional vitamin A supplements.
Also, these drugs can cause serious birth defects.
Women of childbearing age should have two negative pregnancy tests and be on two types of birth control before taking these drugs.
retinoids will be watched closely by their doctor.

Clinical data:
Pharmaceutical class: vitamin
ATC code: A11CA01 (WHO) D10AD02 (WHO), R01AX02 (WHO), S01XA02 (WHO)

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