Vitamin A
VITAMIN A
What is vitamin? Vitamin is the organic compound which is needed by the body in a limited amount but cannot be synthesized by the body instead it can be obtained from dietary sources. The primary function of vitamins are co-enzymes. What are co-enzymes? Co-enzymes are organic compounds, normally vitamins which assists the Co-enzymes are organic compounds, normally vitamins which assists the enzymes to perform their functions. Types of vitamins Water soluble vitamins Fat soluble vitamins The examples of water soluble vitamins are vitamin B and C while the examples of fat soluble vitamins are vitamin A, D, E and K.
VITAMIN A: Is a fat soluble organic compound required by the body for various physiological functions. It cannot be synthesized by the body, needs to be obtained from diet. It occurs in 3 active forms: retinol, retinal, retinoic acid. Retinol is another active form of vitamin A taken up by the cell in the body. Retinol is oxidized in the body cells by enzymes known as Retinol dehydrogenasesto form Retinaldehyde. Retinaldehydeis then oxidized to form retinoic acid. The process of converting retinal to retinoic acid is the irreversible process. retinal to retinoic acid is the irreversible process.
TYPES OF VITAMIN A There are two types of vitamin A these are, i.Preformed vitamin A (retinol, retinal, retinoic acid) ii.ProvitaminA (naturally occurring pigments [orange, yellow, red] known as carotenes or carotenoids; capable of conversion to vitamin A, β-carotenes have higher vitamin A activity than others e.g. α-carotenes, lutein)
DIETARY SOURCES
Preformed vitamin A animal products like liver, meats, eggs, fish, fatty fish liver oils, milk, butter, cheese, kidney.
ProvitaminA ProvitaminA plant products like mango, pawpaw, carrots, pumpkin fruit, red palm oil, dark green leaves [e.g. spinach], red/yellow/orange-fleshed sweet potatoes, oranges, etc
ROLES OF VITAMIN A
Promote good vision Vitamin A play an important role in improving eyes’ good vision, with the help of light- sensitive opsinproteins, forming rhodopsin(in rods) and iodopsin(in cones). Rhodopsinmakes vision in dim light possible [deficiency leads to inability to see in the dark, night blindness]. Iodopsinsserve as colourvisions in bright illumination. •Retinol in blood is oxidisedto retinal which combines with the protein opsinat the rod of the retina to form rhodopsin. As light strikes the retina, retinal separates from opsin and a series of complex biochemical changes results in generation of nerve impulses Retinal + Opsin= Rhodopsin
Maintenance of health immune system Vitamin A is essential for maintaining health and proper immune function and regulation. Barrier immune function in the form of mucosal mucinsecretion is influenced by the vitamin A-dependent expression of synthetic enzymes for glycosaminoglycansand epithelial glycoproteins. Cellular and humoralresponses to immunity are depressed in vitamin A deficiency, leading to impaired response to infections.
Promote proper cell growth (i.e. differentiation and maintenance) Retinoic acid as one the active form of vitamin A is a key compound in promoting proper cell differentiation, growth and maintenance of the epithelial cells and other cells within the body. Epithelial tissues form the outer most layer of skin, eyes and linings of respiratory, reproductive and GIT systems. They need to be replaced frequently.
Vitamin A deficiency results in poor growth of the cells, old tissues not being replaced, decreased mucus production (mucus-secreting cells are replaced by keratin-producing cells, a basis for tissues becoming dry & crusty). This keratin-producing cells, a basis for tissues becoming dry & crusty). This increases susceptibility to a variety of infectious diseases.
Skin health Retinoic acid is used to activate genes that cause the immature skin cells to grow and mature in the epidermal layer of cells. Scientifically the mechanism behind this is currently being researched by the scientists.
Gene transcription and protein formation Retinoic acid binds with the nuclear receptor to regulate gene transcription. Large number of genes are sensitive to control by retinoic acid in different tissues, and at different stages in development; and retinoic acid is essential for the normal responses to vitamin D, thyroid hormone and long-chain polyunsaturated fatty acid (PUFA) derivatives.
Beta-carotene (β-carotene) as an anti-oxidant Beta-carotene (β-carotene) as an anti-oxidant By neutralisingsubstances that are highly reactive and harmful to cell membrane, beta-carotene prevent damage to cells and cellular functions. Under conditions of low oxygen availability, carotenes can act as radical-trapping antioxidants. Epidemiological research have shown evidence that high intakes of carotene are associated with a low incidence of cardiovascular disease and some forms of cancer, although the results are not conclusive [increased incidence of lung cancer was shown among those taking carotene supplements]7
Reproduction Normal spermatogenesis in males and prevention of placental necrosis and foetalresoptionin females require vitamin A. Growth Retinoic acid play its hormone-like function in the control of growth and development of tissues in the musculo-skeletal system Haemopoiesis Haemopoiesis Vitamin A is required for haematologicresponse (absorption, transport or storage of iron). Retinoic acid is necessary for erythrocytes (red blood cells) differentiation. Vitamin A deficiency (VAD) has shown in research to be consistently associated with iron deficiency anaemiawhereas vitamin A supplementation improved haemoglobinconcentration and iron status
ABSOPTION OF VITAMIN A
Dietary preformed vitamin A and carotenoidsare released from protein in the stomach by proteolysis, and combined with lipids and pass into the small intestine to undergo digestion and absorption similar to that of lipids. Vitamin A are solubilized and change into retinal and retinoic acid which are active forms of vitamin A. These active forms of vitamin A are absorbed in the duodenum into blood stream (circulation) via formation of micelles and chylomicrons. Absorbed vitamins will be transported to different party of the body for various physiological functions but others will be converted to retinylesters(storage form of vitamin A) which is stored in the liver.
BODY REQUIREMENT TO VITAMIN A
The amount of vitamin A required by the body depends on several factors such as age, sex, health status, physiological state (pregnant vs. non-pregnant), and other factors. Recommended dietary allowance (RDA) for vitamin A by age are listed in the following table:
AgegroupYears/monthsVitaminAbodyrequirements(in RetinolActivityEquivalent,RAE)
Infants0–6months400mcg/day
7–12months500 mcg/day Children1–3years300 mcg/day
4–8years400 mcg/day 4–8years400 mcg/day
9–13years600 mcg/day
Adolescents andadults
Malesaged14andolder900 mcg/day
Femalesaged14andolder700 mcg/day
Pregnantwomen750 mcg/day
Preformed vitamin A from animal products are readily available and absorbed than vitamin A obtained from plant products, thus are considered best sources of vitamin A. Dietary fat is important for the absorption of carotenes (a minimum of 5 gram fat is required for adequate micelle formation
and absorption).
What is vitamin? Vitamin is the organic compound which is needed by the body in a limited amount but cannot be synthesized by the body instead it can be obtained from dietary sources. The primary function of vitamins are co-enzymes. What are co-enzymes? Co-enzymes are organic compounds, normally vitamins which assists the Co-enzymes are organic compounds, normally vitamins which assists the enzymes to perform their functions. Types of vitamins Water soluble vitamins Fat soluble vitamins The examples of water soluble vitamins are vitamin B and C while the examples of fat soluble vitamins are vitamin A, D, E and K.
VITAMIN A: Is a fat soluble organic compound required by the body for various physiological functions. It cannot be synthesized by the body, needs to be obtained from diet. It occurs in 3 active forms: retinol, retinal, retinoic acid. Retinol is another active form of vitamin A taken up by the cell in the body. Retinol is oxidized in the body cells by enzymes known as Retinol dehydrogenasesto form Retinaldehyde. Retinaldehydeis then oxidized to form retinoic acid. The process of converting retinal to retinoic acid is the irreversible process. retinal to retinoic acid is the irreversible process.
TYPES OF VITAMIN A There are two types of vitamin A these are, i.Preformed vitamin A (retinol, retinal, retinoic acid) ii.ProvitaminA (naturally occurring pigments [orange, yellow, red] known as carotenes or carotenoids; capable of conversion to vitamin A, β-carotenes have higher vitamin A activity than others e.g. α-carotenes, lutein)
DIETARY SOURCES
Preformed vitamin A animal products like liver, meats, eggs, fish, fatty fish liver oils, milk, butter, cheese, kidney.
ProvitaminA ProvitaminA plant products like mango, pawpaw, carrots, pumpkin fruit, red palm oil, dark green leaves [e.g. spinach], red/yellow/orange-fleshed sweet potatoes, oranges, etc
ROLES OF VITAMIN A
Promote good vision Vitamin A play an important role in improving eyes’ good vision, with the help of light- sensitive opsinproteins, forming rhodopsin(in rods) and iodopsin(in cones). Rhodopsinmakes vision in dim light possible [deficiency leads to inability to see in the dark, night blindness]. Iodopsinsserve as colourvisions in bright illumination. •Retinol in blood is oxidisedto retinal which combines with the protein opsinat the rod of the retina to form rhodopsin. As light strikes the retina, retinal separates from opsin and a series of complex biochemical changes results in generation of nerve impulses Retinal + Opsin= Rhodopsin
Maintenance of health immune system Vitamin A is essential for maintaining health and proper immune function and regulation. Barrier immune function in the form of mucosal mucinsecretion is influenced by the vitamin A-dependent expression of synthetic enzymes for glycosaminoglycansand epithelial glycoproteins. Cellular and humoralresponses to immunity are depressed in vitamin A deficiency, leading to impaired response to infections.
Promote proper cell growth (i.e. differentiation and maintenance) Retinoic acid as one the active form of vitamin A is a key compound in promoting proper cell differentiation, growth and maintenance of the epithelial cells and other cells within the body. Epithelial tissues form the outer most layer of skin, eyes and linings of respiratory, reproductive and GIT systems. They need to be replaced frequently.
Vitamin A deficiency results in poor growth of the cells, old tissues not being replaced, decreased mucus production (mucus-secreting cells are replaced by keratin-producing cells, a basis for tissues becoming dry & crusty). This keratin-producing cells, a basis for tissues becoming dry & crusty). This increases susceptibility to a variety of infectious diseases.
Skin health Retinoic acid is used to activate genes that cause the immature skin cells to grow and mature in the epidermal layer of cells. Scientifically the mechanism behind this is currently being researched by the scientists.
Gene transcription and protein formation Retinoic acid binds with the nuclear receptor to regulate gene transcription. Large number of genes are sensitive to control by retinoic acid in different tissues, and at different stages in development; and retinoic acid is essential for the normal responses to vitamin D, thyroid hormone and long-chain polyunsaturated fatty acid (PUFA) derivatives.
Beta-carotene (β-carotene) as an anti-oxidant Beta-carotene (β-carotene) as an anti-oxidant By neutralisingsubstances that are highly reactive and harmful to cell membrane, beta-carotene prevent damage to cells and cellular functions. Under conditions of low oxygen availability, carotenes can act as radical-trapping antioxidants. Epidemiological research have shown evidence that high intakes of carotene are associated with a low incidence of cardiovascular disease and some forms of cancer, although the results are not conclusive [increased incidence of lung cancer was shown among those taking carotene supplements]7
Reproduction Normal spermatogenesis in males and prevention of placental necrosis and foetalresoptionin females require vitamin A. Growth Retinoic acid play its hormone-like function in the control of growth and development of tissues in the musculo-skeletal system Haemopoiesis Haemopoiesis Vitamin A is required for haematologicresponse (absorption, transport or storage of iron). Retinoic acid is necessary for erythrocytes (red blood cells) differentiation. Vitamin A deficiency (VAD) has shown in research to be consistently associated with iron deficiency anaemiawhereas vitamin A supplementation improved haemoglobinconcentration and iron status
ABSOPTION OF VITAMIN A
Dietary preformed vitamin A and carotenoidsare released from protein in the stomach by proteolysis, and combined with lipids and pass into the small intestine to undergo digestion and absorption similar to that of lipids. Vitamin A are solubilized and change into retinal and retinoic acid which are active forms of vitamin A. These active forms of vitamin A are absorbed in the duodenum into blood stream (circulation) via formation of micelles and chylomicrons. Absorbed vitamins will be transported to different party of the body for various physiological functions but others will be converted to retinylesters(storage form of vitamin A) which is stored in the liver.
BODY REQUIREMENT TO VITAMIN A
The amount of vitamin A required by the body depends on several factors such as age, sex, health status, physiological state (pregnant vs. non-pregnant), and other factors. Recommended dietary allowance (RDA) for vitamin A by age are listed in the following table:
AgegroupYears/monthsVitaminAbodyrequirements(in RetinolActivityEquivalent,RAE)
Infants0–6months400mcg/day
7–12months500 mcg/day Children1–3years300 mcg/day
4–8years400 mcg/day 4–8years400 mcg/day
9–13years600 mcg/day
Adolescents andadults
Malesaged14andolder900 mcg/day
Femalesaged14andolder700 mcg/day
Pregnantwomen750 mcg/day
Preformed vitamin A from animal products are readily available and absorbed than vitamin A obtained from plant products, thus are considered best sources of vitamin A. Dietary fat is important for the absorption of carotenes (a minimum of 5 gram fat is required for adequate micelle formation
and absorption).
No comments: