This document discusses vitamin A, including its classification, sources, absorption, transport, storage, functions, deficiency, toxicity, and recommended daily intake. Some key points: - Vitamin A is a fat-soluble vitamin that is essential for vision, growth, reproduction, and epithelial cell maintenance. It cannot be made by the body and must come from diet. - Major sources include liver, dairy, eggs, carrots and other orange vegetables. Beta-carotene from plants is a provitamin A that the body can convert to vitamin A. - It is absorbed in intestinal cells and transported to the liver bound to retinol binding protein in the bloodstream. The liver stores significant amounts. -

1. Dr. P. N. ANSIL

2. What are vitamins ?
 Essential organic compounds that are required in small
amounts for normal growth, maintenance of good health
and for the proper utilization of other nutrients.
 Nutrients that our body does not make on its own. Thus
we must obtain them from the foods we eat, or via vitamin
supplements.

3. VITAMINS
Fat Soluble
Vitamin A
Vitamin D
Vitamin E
Vitamin K
Water Soluble
B-Complex
Energy
releasing
Thiamine
Riboflavin
Niacin
Pyridoxine
Biotin
Pantothenic
acid
Hematopoietic
Folic acid
Vitamin
B12
Non B-
Complex Vitamin C
Classification of
Vitamins

4. Fat soluble vitamins
• Soluble in fat
• Absorbed along with other lipids
• Requires carrier proteins
• Stored in liver
• Deficiency manifests only when
stores are depleted
• Toxicity - Hypervitaminosis may
result
• Single large does may prevent
deficiency
• E.g. A,D,E & K
• Soluble in water
• Absorption is simple
• No requirement of carrier protein
• Excreted in urine
• Deficiency manifests rapidly as
there is no storage
• Unlikely , since excess is excreted
• Regular dietary supply is required
• E.g. B complex & C
Difference between fat soluble and water soluble vitamins
Water soluble vitamins

5.  Hydrophobic
 Isoprene derivatives
 They cannot be synthesized by the body
 Supplied by the diet
 Absorption along with fat
 Transport: By lipoprotein & Specific binding protein
 Surplus amount stored – liver & adipose tissue
 Excess consumption leads to accumulation & toxic effects.
Lipid soluble vitamins - common features

6. VITAMIN A

7. Introduction
• Vitamin A is an essential nutrient needed in small amounts
for the normal functioning of the visual system, and
maintenance of cell function for growth, epithelial integrity,
red blood cell production, immunity and reproduction.
• Vitamin A deficiency (VAD) is a major nutritional concern in
poor societies, especially in lower income countries like
INDIA.

8. Where does it come from?
Animal Sources
 Eggs
 Meat
 Cheese
 Milk
 Liver
 Kidney
 Fish liver oils
Plant Sources
 Carrots
 Sweet Potatoes
 Apricots
 Broccoli
 Spinach
 Pumpkin
 Papaya
 Mango

9. Vitamin A
(Preformed and Provitamin)
• Retinoids: Natural & synthetic forms of Vitamin A
• Preformed: Three preformed compounds that are metabolically
active and found in animal products
– Retinol – alcohol form
– Present in animal tissues as retinyl ester with long chain
fatty acid
– Retinal or retinaldehyde – aldehyde form
– Obtained by oxidation of retinol
– Retinal & Retinol are interconvertible
– Retinoic acid – acid form
– Produced by oxidation of Retinal

10. • Provitamin: Carotenoids (β-carotene) can yield 2
retinols when metabolized in the body
• β -carotene
 found in plants
 Has 2 β-ionone rings connected by a polyprenoid
chain

13. Absorption
• Retinoids
– Retinyl esters broken down to free retinol & FA in small
intestine - requires bile, digestive enzymes, integration into
micelles
– Once absorbed, retinyl esters reformed in intestinal cells
– 90% of retinoids can be absorbed
• Carotenoids
– Absorbed intact, absorption rate much lower
– Intestinal cells can convert carotenoids to retinoids

14. • Approximately 80% is absorbed.
• It is passed along with fat through the lymphatic system
into blood stream.
• Absorption is poor in case of diarrhea, jaundice and
abdominal disorder.
• Absorption increases if taken with fat.
• Vitamin A which is not absorbed is excreted within 1 or 2
days in feces .

15. Transport
• Transported via chylomicrons from intestinal cells to the
liver
• Transported from the liver to target tissue as retinol via
retinol-binding protein (RBP; MW. 21,000).
From intestine to Liver
From liver to tissue
Plasma retinol binding protein(RBP)– to cell membrane-
Cellular retinoic-acid binding protein(CRBP) –retinol—
cytoplasm—HRE—GENE EXPRESSION
Chylomicron

17. Summary of Vitamin A
absorption

18. Summary of the functions of Vitamin A
compounds

19. Storage
• The liver has enormous capacity to store in the form of
retinol palmitate.
• Under normal conditions a well-fed person has sufficient
Vitamin A reserves to meet his need for 6 to 9months or
more.

20. Excretion of Vitamin A
• Not readily excreted
• Kidney disease and aging increase risk of toxicity because
excretion is impaired

21. Functions of Vitamin A
 Vision: Vitamin A is a component of the visual pigment
rhodopsin. Retinal is bound to the protein opsin.
 Growth: Vitamin A deficiency causes loss of appetite. Slow
bone growth. Affects CNS.
 Reproduction: Retinol and retinal are essential for normal
reproduction
 Maintenance of epithelial cells: Essential for normal
differentiation of epithelial tissues and mucus secretion

22. Role of Vitamin A in Vision
Visual Cycle (Wald’s Visual Cycle)
 A process by which light impacting on the retina of the eye
is converted to an electrical signal
 The optic nerve carries the electrical signal to the brain
(nerve impulse)
 The brain processes the signal into an image

23. Role of Vitamin A in Vision
 Retina is a light-sensitive layer of cells at the back of the
eye where an image is formed
 Retina consists of: Rod and cone cells (photosensitive
cells)
 Rod cells process & image
 Cone cells process color image

25. Rod Cell
Cone Cell

26. Role of Vitamin A in Vision
 Normal vision depends on the retina and on adequate
vitamin A
 In the retina, vitamin A in the form of retinal binds to a
protein called opsin to make rhodopsin [11-cis – retinal-
opsin] in rod cells
 Rhodopsin is a light-sensitive pigments

27. Wald’s Visual Cycle

28. The Visual
Cycle

29. Role of Vitamin A in Vision
 When stimulated by light, vitamin A isomerizes from its
bent ‘cis’ form to a straighter ‘trans’ form and detaches
from opsin
 The opsin molecule changes shape, which sends a signal to
the brain via optic nerve and an image is formed
 Most retinal released in this process is quickly converted to
trans-retinol and then to cis-retinal, to begin another cycle

30. Role of Vitamin A in Vision
Dark Adaptation time
 Bright light depletes rhodopsin (photobleaching)
 Sudden shift from bright light to darkness causes
difficulty in seeing
 Rhodopsin is synthesized in a few minutes and vision is
improved in the dark

31. Role of Vitamin A in Vision
 The time required to synthesize rhodopsin in the dark is
called dark adaptation time
 It is increased in vitamin A deficiency

32. Bleaching of Rhodopsin
• Bleaching - When exposed to light, the colour of
rhodopsin changes from red to yellow
• Occurs in a few milliseconds
• Unstable intermediates are formed
Rhodopsin Prelumirhodopsin Lumirhodopsin
Metarhodopsin IMetarhodopsin IIAll-trans-retinal +
Opsin

33. • Light strikes the retina – biochemical changes –
membrane hyperpolarization – generate nerve impulse.
• Hyperpolarization of the membrane is brought about by
a visual cascade involving cGMP
Visual cascade and cGMP

34. Visual cascade involving cGMP
• Decrease in cGMP closes
the Na+ channels in the
membranes of the rod
cells
• Result in
hyperpolariztion – an
excitatory response
transmitted through the
neuron network to the
visual cortex of the
brain

35. Colour vision
• Cones are specialized in bright and colour vision
• Governed by colour sensitive pigmens
iodopsin – green
cyanopsin – blue
porphyropsin – red
• These pigments are complexes of protein & Vitamin A
• Bright light strikes retina – depending on the
particular colour of the light – one or more pigments
are bleached – passes nerve impulse to brain as
specific colour

36. Functions of Vitamin A:
Growth and Differentiation of Cells
• Retinoic acid is necessary for cellular differentiation
• Important for embryo development, gene expression
• Retinoic acid influences production, structure, and
function of epithelial cells that line the outside (skin)
and external passages (mucus forming cells) within the
body

37. Epithelial cell ‘integrity’
• Many epithelial cell require Vitamin A for proper
differentiation and maintenance
• Lack of Vitamin A leads to dysfunction of epithelia
– The skin becomes keratinized and scaly, and mucus
secretion is suppressed

39. Functions of Vitamin A: Immunity
• Deficiency leads to decreased resistance to infections
• Supplementation may decrease severity of infections in
deficient person

40. • Role in Prevention of cardiovascular disease
– Antioxidant capabilities
• Role in Cancer prevention
– Antioxidant capabilities
– Lung, oral, and prostate cancers
– Studies indicate that vitamin A-containing foods are more
protective than supplements

41. What does RDA mean?
• Recommended Dietary Allowances
• These are suggested levels of essential nutrients
considered adequate to meet nutritional needs of healthy
individuals.
Infants and children - 400-600µg/day
Men -750-1000µg/day
Women -750µg/day
Pregnancy -1000µg/day
Lactation -1200µg/day

42. Vitamin A Deficiency and Diseases
 Nyctalopia (night blindness)
 Xerophthalmia
 Bitot’s spots
 Keratomalacia
 Complete blindness (in severe deficiency)

43. 1. Night Blindness
• Visual acuity is diminished in dim
light
• Occurs as a result of inadequate
pigment in the retina.
• The dark adaptation time is
increased
• Found in pregnant women in
some instances, especially during
the last trimester of pregnancy
when the vitamin A needs are
increased.

44.  It is the most specific VAD,
and is the leading
preventable cause of
blindness
 Conjunctiva becomes dry,
thick and wrinkled
 Conjunctiva gets keratinized
and loses its normal
transparency
 Cornea becomes glazy &
lusterless
2. Xerophthalmia

45. 3. Bitot’s Spot
• Tissue spots that develop around
the eye ball, causing severe
dryness in the eyes.
• Seen as grayish-white triangular
plaques firmly adherent to the
conjunctiva.

46. 4.Keratomalacia
• One of the major cause for
blindness in India.
• Cornea becomes soft and may
burst
• Prolonged xerophthalmia
leads to keratomalacia
(softening of the cornea)
• If the eye collapses vision is
lost.

47. Other Symptoms of VAD
• Alteration of skin and mucous membrane
• Hepatic dysfunction
• Headache
• Drowsiness
• Peeling of skin

48. • Dark adaptation test
• Serum RBP
• Serum vitamin A
25 – 50 µg/dl
ASSESSMENT OF DEFICIENCY

49. 1) Eating of polar bear liver
2) Excess supplementation of
Vitamin A
When?
TOXICITY
One ounce of polar bear
liver contains enough
vitamin A (retinol) to kill a
person!

50. • Hepatomegaly
• Increased cerebrospinal fluid pressure
• Disturbance in calcium homeostasis – skletal
decalcificaion – tendrness of long bones
• Skin - Excessive dryness, desquamation
TOXICITY

51. 1.Dietary Deficiency
2. Retinoic acid
a. Psoriasis
b. Pro-myelocytic leukemia
c. Acne
THERAPEUTIC USES

52. Thank you