Vitamins, types, and functions

Vitamins are defined as
"small organic molecules present in diet which are
required in small amounts. "
• Most of the vitamins are not synthesized in the body and
hence they must be supplied in the diet.
• However few vitamins are synthesized in the body.
Though most of them are present in diet as such some
are present as precursors.
• The precursor forms of vitamins are called as
provitamins. In the body these provitamins are converted
to vitamins.

Classification of Vitamins
• Vitamins are divided into two groups.
1. fat soluble vitamins
2. water soluble vitamins.
Fat Soluble Vitamins
• They are vitamins A, D, E and K. They have some common
properties.
They are:
1. Fat soluble.
2. Require bile salts for absorption.
3. Stored in liver.
4. Stable to normal cooking conditions.
5. Excreted in feces.

Water Soluble Vitamins:
• They are members of vitamin B complex and Vitamin C.
Their common properties are
1. Water solubility.
2. Except Vitamin B12 others are not stored.
3. Unstable to normal cooking conditions.
4. Excreted in urine.

BIOLOGICAL IMPORTANCE
1. Vitamins are essential for growth, maintenance and
reproduction. However, they are not used for energy
production.
2. Fat soluble vitamins are required for normal colour vision,
blood clotting, bone formation and maintenance of membrane
structure.
3. Most of the water soluble vitamins function as coenzymes or
prosthetic groups of several enzymes involved in
carbohydrate, lipid and amino acid metabolism etc.
4. Vitamins A and D act as steroid hormones.
5. Deficiency of fat soluble vitamins produce night blindness,
skeletal deformation, haemorrhages and hemolysis.

BIOLOGICAL IMPORTANCE (Cont..)
6. Deficiency of water soluble vitamins produce beriberi,
glossitis, pellagra, microcytic anaemia, megaloblastic
anaemia and scurvy.
7. Some vitamin analogs are used as drugs. For example folic
acid analogs are used as anticancer agents and antibiotics.
8. Moderate consumption of some vitamins is found to decrease
occurrence or severity of some diseases.
For example carotenes, Vitamin E and Vitamin D
consumption at moderate evel reduces incidence of cancer
and cardiovascular diseases.

BIOLOGICAL IMPORTANCE (Cont..)
9. Consumption of vitamin C in significant amounts reduces
severity of cold. They slow down ageing process also.
However, excessive consumption of fat soluble vitamins leads
to toxicity.
10.Vit B12, Folic acid and Vit B6 are beneficial to coronary artery
disease patients. They lower plasma homocysteine levels.

WATER SOLUBLE VITAMINS
VITAMIN B COMPLEX
Members of vitamin B complex are
(1) Thiamin (Vitamin B1)
(2) Riboflavin (Vitamin B2)
(3) Niacin
(4) Pyridoxine (Vitamin B6)
(5) Biotin
(6) Folic acid
(7) Cyanocobalamin (Vitamin B12)
(8) Pantothenic acid.

VITAMIN B COMPLEX
THIAMIN
Chemistry
• It is a heat labile sulfur containing vitamin. It contains
pyrimidine ring and thiazole ring
• which are joined by methylene bridge. It is highly alkaline
sensitive.
Absorption and Transport
• It is absorbed in small intestine by active transport mechanism
and simple diffusion. Then it reaches liver through circulation.

THIAMIN
Function
• Thiamin pyrophosphate (TPP or TDP) is the active form of
thiamin.
• It is formed from thiamin in presence of ATP in a reaction
catalyzed by thiamin kinase present in liver.
• TPP is the prosthetic group of enzymes like pyruvate
dehydrogenase, α-keto glutarate dehydrogenase etc.

THIAMIN
Sources
• Rich Sources. Outer coatings of food grains like rice,
wheat and yeast.
• Good sources. Whole cereals, pulses, oilseeds and
nuts.
• Fair sources. Meat, liver and egg and fish.
Thiamine Deficiency
1. Adult beriberi. Early signs of beri beri are insomnia,
headache, dizziness, loss of appetite, muscle weakness,
numbness and pricking sensation in lower limbs and
fatigue.

Thiamine Deficiency
If not treated it leads to
(a) Wet beri beri. In which cardiovascular system is affected and
it is characterized by edema.
Edema appears in lower limbs, trunk, face and serous
cavities. Blood pressure becomes abnormal. Heart becomes
weak and death occurs due to heart failure.
(b) Dry beri beri. In which central nervous system is affected. In
addition to early signs severe muscle wasting occurs. As a
result individual is unable to walk and becomes bed ridden.
Death may occur if not treated.
2. Infantile beri beri. In infants thiamine deficiency causes
infantile beri beri. It occurs in infants between 2-10 months of
age.

VITAMIN B COMPLEX
Riboflavin (Vitamin B2)
Chemistry
• It contains heterocyclic isoalloxazine ring and ribitol a sugar
alcohol. It is sensitive to light and alkali but stable to heat and
acidic medium.

• Absorbed in small intestine and distributed to all tissues by
circulation.
Functions
• Active forms of riboflavin are FMN and FAD. They act as
prosthetic groups of several enzymes. FMN is flavin
mononucleotide and FAD is flavin adenine dinucleotide.They
act as carriers of hydrogen atoms in redox reactions.
Sources
• Whole grains, legumes, pulses, green leafy vegetables, yeast,
eggs, milk and meat are good sources.
• Root vegetables and fruits are fair sources.

Riboflavin Deficiency
• In humans riboflavin deficiency causes oral, facial, occular
lesions.
(a) Angular Stomatitis. Lesions of mouth particularly at corners of
mouth.
(b) Cheliosis. Red swollen and cracked lips.
(c) Vascularization of cornea and conjuctiva and blood shot
eyes.
(d) Glossitis. Inflammated magenta coloured tongue.

NIACIN
Chemistry
• The word niacin refers to two pyridine derivatives. They are
nicotinic acid and nicotinamide.
• Both are highly stable to heat and stable to alkali and acid.
Absorption and transport
• Nicotinic acid and nicotinamide are absorbed in small
intestine and reach various tissues through circulation where
they are converted to NAD and NADP.

Niacin
Functions
• Nicotinamide is component of two coenzymes NAD and
NADP. NAD is nicotinamide adenine dinucleotide and NADP
is nicotinamide adenine dinucleotide phosphate.
Sources
• Whole grains, peanuts, legumes, yeast, liver, fish and meat
are good sources.
• Milk and egg are poor source of niacin but rich source of
tryptophan. Vegetables and fruits are poor source of niacin.
Niacin Deficiency
• Niacin deficiency causes pellagra in which skin,
gastrointestinal tract and nervous system are affected.
• Dermatitis, Diarrhoea and Dementia are characteristic
symptoms of pellagra.

PYRIDOXINE
Chemistry
• Three compounds derived from pyridine show vitamin B6
activity. They are pyridoxine, pyridoxal and pyridoxamine.
Pyridoxine is stable to heat and sensitive to light and alkali.
• Pyridoxine is easily absorbed and reaches various tissues
through circulation. In the tissues pyridoxine is converted to
pyridoxal and pyridoxamine.

PYRIDOXINE
Functions
• Pyridoxal phosphate is active form. It is formed from pyridoxal
by phosphorylation catalyzed by pyridoxal kinase.
• Pyridoxal phosphate act as prosthetic group or co enzyme of
enzymes which are involved in transamination,
decarboxylation, transsulfuration, desulfuration and non-
oxidative deamination reactions.
• Pyriodoxal phosphate is coenzyme for enzymes that are
involved in the synthesis of heme, serotonin, catecholamines
and coenzyme A synthesis.

PYRIDOXINE
Sources
• Whole grains, legumes, liver and yeast are good sources.
Leafy vegetables, milk, meat and eggs are fair sources.
Pyridoxine Deficiency
1. It is rare in human adults.
2. In children vitamin B6 deficiency causes epileptic form
convulsions (seizures) due to decreased formation of neuro
transmitters like GABA, serotonin and catecholamines.

BIOTIN
Chemistry
• It is a sulfur containing vitamin. It consist of imidozole ring
fused to tetrahydro thiophene with valerie acid side chain. It is
stable to heat but alkaline sensitive.
• It is absorbed in the small intestine and reaches liver and
other tissues through circulation.

Function
• Biotin is prosthetic groups of several carboxylases like
pyruvate carboxylase, acetyl-CoA carboxylase, propionyl-CoA
carboxylase etc.
• Biotin is attached to e-aminogroups of Iysyl residue of
apoenzyme through, amide linkage. In carboxylation reaction
it acts as a carrier of CO2
Dietary sources
• Whole cereals, legumes, groundnuts, milk, meat and fish are
good sources. Vegetables and fruits are fair sources.
Biotin deficiency
• Biotin deficiency is rare in humans because it is present in
most of the common foods.

FOLIC ACID
Chemistry
• Folic acid consist of pteridine nucleus, p-aminobenzoic acid
and glutamate. It is sensitive to light and acid but stable to
heat and alkali.
• Folic acid present in natural foods is called as folyl
polyglutamate. In the intestinal mucosal cells hydrolase form
folic acid which is reduced to N5 - methyl tetrahydrofolate.
• Methyl tetrahydrofolate is the major circulating form probably
bound to protein.

Function
• Tetrahydrofolate or FH4 which is reduced form of folic acid is
carrier of one carbon units.
• Folic acid is required for the synthesis of DNA through
nucleotides particularly TMP formation, in rapidly dividing cells
like bone marrow or erythropoietic cells or intestinal cells.
• Folic acid prevents neural tube defects (NTD) that occur
during fetal development.
Sources
• Green leafy vegetables like spinach, cabbage, ladyfinger,
curry and mint leaves, pulses like black gram, green gram,
eggs and liver are good sources. Coconuts, whole cereals
and milk are fair sources.

Folic Acid Deficiency
• Megaloblastic anaemia is the main symptom of folic acid
deficiency. It is most common in pregnant women and in
unweaned children.

CYANOCOBALAMIN (VITAMIN B12)
Chemistry
• It has complex chemical structure. It is made up of
Tetrapyrrole ring system called as corrin ring with a central
cobalt (Co) atom with molecular formula (C63 H88 N14 O14 PCO)

• The absorption of vitamin B12 takes place in ileum.
Transcobalamin II delivers vitamin B12 to tissues.
Storage
• Unlike other water soluble vitamins vitamin B12 is stored in the
liver and other tissues.
Functions
• Vitamin B12 act as prosthetic group or coenzyme.
Vitamin B12 Deficiency
• Vitamin B12 deficiency affects bone marrow, intestinal tract
and neurological system. In vitamin B12 deficiency these
systems are affected because DNA synthesis, methionine
synthesis and fatty acid synthesis are altered.

PANTOTHENIC ACID
Chemistry
• It is an amide of β-alanine and dihydroxy dimethyl butyric acid
(Pantoic acid)
• It is stable to heat but unstable to alkali or acid.
• Intestinal phosphatases release pantothenic acid from dietary
sources.
• Free pantothenate or its salts are freely absorbed in the
intestine and reach various tissues through circulation.

Functions
• Pantothenic acid is a component of coenzyme A. Coenzyme
(CoA) participates in several enzymatic reactions of
carbohydrate, lipid and amino acid metabolism.
• It serves as carrier of acyl groups during fatty acid
biosynthesis.
Pantothenic acid deficiency
• It cause burning feet, abdominal cramps, restlessness and
fatigue in humans.
Sources
• Organ meat, liver, milk, whole cereals, legumes and eggs are
good sources. Vegetables and fruits are poor sources.

VITAMIN C (ASCORBIC ACID)
Chemistry
• It is a sugar acid known as hexuronic acid. Ascorbic acid is
easily oxidized by atomospheric O2 to dehydroascarobic acid
• High temperature (cooking) accelerates oxidation.
• Light and alkali also promotes oxidation.
• Vitamin C is readily absorbed in the intestine by sodium
dependent active transport mechanism and reaches various
body tissues through circulation. Ascorbic acid enters various
cells like erythrocytes, leucocytes etc. freely.

Functions
1. Ascorbic acid act as antioxidant. It is free radical scavenger.
Since it is a strong reducing agent it protects carotenes,
vitamin E and other B vitamins of dietary origin from oxidation.
2. It is required for the hydroxylation of proline and lysine
residues of collagen. Since collagen is component of ground
substance of capillaries, bone and teeth vitamin C is required
for proper bone and teeth formation also.
3.It participates in hydroxylation reactions of steroid
biosynthesis.
4. It is required for catecholamine synthesis from tyrosine.
5. In the liver bile acid synthesis requires ascorbic acid.

6. It is required for the absorption of iron in the intestine. It
maintains iron in ferrous form.
7. Catabolism of tyrosine requires ascorbic acid.
8. Vitamin C is effective in controlling bacterial invasion by
inhibiting activity of bacterial hyaluronidase enzyme. It acts as
inhibitor of this enzyme due to structural similarity to
glucuronate of hyaluronin, the substrate of hyaluronidase.

Vitamin C deficiency
1. In adults deficiency of vitamin C causes scurvy. But it rarely
occurs in normal people.
The symptoms of scurvy are
(a) Haemorrhages in various tissues particularly in inside of
thigh, calf and forearm muscles. It may be due to capillary
fragility.
(b) General weakness and anaemia.
(c) Swollen joints, swollen gums and loose tooth.
(d) Susceptible for infections.
(e) Delayed wound healing.
(f) Bone fragility and osteoporosis.
2. Vitamin C deficiency in infants gives rise to infanitle scurvy. It
occurs in weaned infants who are fed on diets low in vitamin
C.

Sources
• Guava, coriander and amarnath leaves, and cabbage are rich
• sources. Fruits like lemon, orange, pineapple, papaya, mango
and tomato are good sources.
• Apples, bananas and grapes are fair sources.

FAT SOLUBLE VITAMINS
VITAMIN A
Chemistry
• They are retinol (Vitamin A alcohol), retinal (Vitamin A
aldehyde) and retinoic acid (Vitamin A acid).
• They are composed of β−ionine ring (methyl substituted
cyclohexenyl ring) and side chain containing two isoprene
units with four conjugated double bonds.
• Due to the presence of double bonds in isoprenoid side chain
vitamin A exhibits cis-trans (geometric) isomerism.
• Due to the presence of 4 double bonds vitamin A can be
oxidized by air or light slowly.

VITAMIN A
In nature vitamin A occurs in two forms
• retinolesters -In the foods of animal origin.
• carotenes - in plant foods as provitamin.
Absorption of Vitamin A
• In the intestine pancreatic esterase hydrolyzes retinolesters
present in the diet to retinol and free fatty acid in presence of
bile salts. Retinol is absorbed by mucosal cells.
• Dietaryβ-carotene is cleaved into two molecules of retinal by a
dioxygenase present in the intestinal mucosal. It is
transported by lipoprotein.

Functions of vitamin A
The three major retinoids retinal, retinol and retinoic acid have
unique functions.
1. Retinal is required for normal and color vision.
2. Retinol is required for reproduction and growth.
3. Retinol is required for differentiation and function as steroid
hormone.
4. Retinoic acid is required for the synthesis of glycoproteins or
mucopolysaccharides.
5. Retinoic acid also act as steroid hormone. It also promote
growth and differentiation.
6. Retinol and retinoic acid are involved in regulation of gene
expression.

Retinal and colour vision
• Three light sensitive pigments present in cones are
responsible for colour vision. They are porphyropsin, iodopsin
and cyanopsin.
• All three pigments contain 11-cis retinal and are sensitive to
red, green and blue colours respectively.
• When the photon (light) strikes retina depending on the colour
of the light a particular pigment is bleached. This leads to
generation of nerve impulse and perception of colour by brain.
• Defective apoprotein production due to faulty genes leads to
colour blindness.

Deficiency of Vitamin A
1. Night blindness
• In early stages, the affected individual is not able to see
clearly in dim light or night due to block in the resynthesis of
rhodopsin.
• In the later stage of deficiency the affected individual cannot
see or read in dim light.
• Thus loss of night vision (night blindness) is the major initial
symptom of Vitamin A deficiency.
• Night blindness in adults or in preschool children is common
in countries where intake of vitamin A is low.
2. Growth of bone and formation of tooth are defective. Thick
and long bones are formed.
3. Nerve growth also affected. Degeneration of myelin sheath
occurs.

Deficiency of Vitamin A
4. Keratinisation of mucous secreting epithelial cells
(hyperkeratosis) lining respiratory tract and reproductive tract
occurs. Mucous secretion by salivary and lacrymal glands is
also affected.
5. Deposition of keratin in skin (xeroderma) gives rise to
characteristic toad skin appearance.
6. Reproductive disorders like testicular degeneration, resorption
of foetus or foetal malformation are observed.
7. Degenerative changes in kidneys.

Sources
(a) Animal sources.
• Marine fish oils like halibut liver oil, cod liver oil and shark liver
oils are excellent sources. Liver of sheep or goat is also
excellent source. Butter, egg, and milk are good sources.
Freshwater fish contain Vitamin A2 (dehydroretinol) which is
only 40% active.
(b) Plant sources. In plant foods vitamin A is present as
carotenes. Plant oil like red palm oil is excellent source.
• Leafy vegetables. coriander leaves, curry leaves, spinach and
cabbage are good sources.
• Yellow vegetables like carrot, pumpkin and sweet potato and
ripe tomatoes also contain appreciable amounts of vitamin A.
• Fruits. Yellow pigmented fruits papaya, mango, jackfruit,
banana and oranges also contain vitamin A in good amounts.

VITAMIN D
Chemistry
• It is also called sunshine vitamins.
• Its active forms are vitamin D2 (ergo calciferol) and vitamin D3
(cholecalciferol).
• Calcitriol is the most active form of vitamin D that acts as
steroid hormone.
• They are formed from provitamins which are sterols.
Absorption, transport and storage
• Dietary vitamin D2 and vitamin D3 are absorbed in the small
intestine in presence of bile salts.
• Absorbed Vit D is incorporated into chylomicrons and enters
circulation via lymph.
• Vitamin D is stored in liver and adipose tissue.

Functions of calcitriol
1. Major action of calcitriol is to increase absorption of calcium
and phosphate in the intestine particularly in duodenum and
jejunum.
2. Calcitriol is required for bone formation and mineralisation of
bone. It increases synthesis of osteocalcin a calcium binding
protein of bone. Osteocalcin is involved in deposition of
calcium salts in bone.
3. Calcitriol affects calcium and phosphorus excretion by kidney.
It reduces the excretion of calcium and phosphorus.
4. Vitamin D is involved in maintenance of normal muscle tone.
5. Calcitriol is an immuno regulatory hormone. It stimulates cell
mediated immunity. It plays a vital role in
monocyte/macrophage activation.

Vit D deficiency symptoms
1. Rickets
• In children vitamin D deficiency causes rickets, results in soft
bones. This leads to deformities in skull, chest, spine, legs
and pelvis.
2. Osteomalacia
• Vitamin D deficiency causes osteomalacia in adults. It is seen
in pregnant women and women with inappropriate diet.
Skeletal pain is early sign. Deformities of ribs, spine, pelvis
and legs are seen.
3. Osteoporosis
• Vitamin D deficiency causes osteoporosis in old people.
Photolysis of provitamins dcreases with age. This and
together with decreased sex hormone production may lead to
deficiency.
• Symptoms are bone pain and porous bones. Bone fractures
are common.

Sources
• Vitamin D is mostly present in foods of animal origin.
• Marine fish liver oils like halibut liver oil, cod liver oil and shark
liver oil are good sources.
• Sardines, egg yolk and butter contains small amounts.
However, milk is a poor source of vitamin D, Mushrooms
contain small amounts of vitamin D.
Toxicity (Hyper vitaminosis)
• Ingestion of mega doses of vitamin D results in toxicity of Vit
D.
• Signs and symptoms of vitamin D toxicity are loss of appetite,
nausae, thirst, vomiting, polyuria and calcification of lungs,
renal tubules and arteries. Muscle wasting also occurs.
Demineralisation of bone similar to vitamin D deficiency is
seen.

VITAMIN E
Chemistry
• Chemically they are tocopherol
• They are derivatives of tocol or 6-hydroxy chromane ring with
phytyl side chain.
• Tocopherols are alkaline sensitive and their vitamin activity is
destroyed by oxidation.
• Among all tocopherols α-tocopherol is most potent and widely
distributed in nature.
• Cooking and food processing may destroy vitamin E to some
extent.

Absorption, transport and storage
• Dietary tocopherols are absorbed in small intestine in the
presence of bile salts.
• Absorbed tocopherols are incorporated into chylomicrons in
mucosal cells of intestine and enters circulation via lymph.
• In plasma tocopherols are released from chylomicrons by
lipoprotein lipase.
• Liver takes up half of tocopherol and it is stored.
• Skeletal muscle and adipose tissue also stores vitamin E.
• From the liver tocopherols are transported to other tissues in
β-lipoprotein.

Functions of Vitamin E
1. α-tocopherol in cell membrane and cytosol function as
antioxidant. It is present in high concentration in tissues which
are exposed to high O2 pressure like erythrocytes, lungs,
retina etc.
• It acts as chain breaking antioxidant.
2. Vitamin E is involved in maintenance of muscle tone
3. Vitamin E increases synthesis of hemeproteins
4. Vitamin E prevents dietary vitamin A and carotenes from
oxidative damage.
Sources
• Cereal germ oils like wheat germ oil, corn germ oil and
vegetable oils like coconut oil, sun flower oil, peanut oil,
ricebran oil, palm oil, mustard oil, cotton seed oil and
soyabean oil are rich sources of vitamin E.
• Vegetables, fruits and meat are relatively poor sources of
vitamin E.

VITAMIN K
Chemistry
• Chemically they are quinones
• Vitamin K1 also called as phylloquinone, is the major form of
vitamin found in plants particularly in green leafy vegetables.
• Vitamin K2 also known as menaquinone is the vitamin K
present in animals and synthesized by intestinal flora.
• They are derivatives of naphthoquinone and differ in side
chain.
• Phylloquinone contain phytylside chain where as
• menaquinone contains polyisoprenoid side chain made up of
7 isoprene units.

• Vitamin K of dietary origin is absorbed in small intestine in
presence of bile salts.
• In mucosal cells of intestine absorbed vitamin K is
incorporated into chylomicrons.
• It reaches liver after entering circulation through the lymph.
• Liver distributes vitamin K to other tissues.
• It rarely accumulates in liver and peripheral tissues.
Sources
Plant Sources
• Cauliflower, Cabbage, spinach, turnip greens, peas and
soybean are rich sources.
Animal sources
• Dairy products like cheese, butter and farm products like eggs
and liver are good sources.

Functions of Vitamin K
• Vitamin K is required for the synthesis of blood clotting factors
like prothrombin (factor II), cothromboplastin (factor VII),
(factor IX) and (factor X).
• It is required for the carboxylation of the γ-carbon atom of
glutamic residues of these factors. The γ-carboxylation
generates calcium binding sites which is essential for blood
clotting process.

Deficiency Symptoms of vitamin K
1. Haemorrhage in the new born is most common vitamin K
deficiency symptom. uncontrolled bleeding through nose
(epitaxis) and gastrointestinal tract is likely to occur. However
it can be treated successfully with intra muscular injections of
vitamin K.
2. In adults vitamin K deficiency rarely occurs. However
prolonged use of antibiotics may cause vitamin K deficiency
due to elimination of intestinal flora.

Vitamins, types, and functions

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Vitamins, types, and functions