Vitamin A plays a vital role in vision, cell growth, immune function, and reproduction. It exists in two forms - preformed vitamin A in animal foods like liver, eggs and dairy, and provitamin A carotenoids in plant foods like fruits and vegetables. Vitamin A deficiency can lead to night blindness and increased susceptibility to infection in children, and cause developmental complications during pregnancy. The document discusses vitamin A's functions, sources, recommended intake levels, deficiency symptoms and toxicity risks.

1. VITAMIN A
Mrs.Nagamani.T, MSc Nursing
Quality Health Care College of Nursing

2. Introduction
• Vitamin A is a fat-soluble nutrient that plays a vital role in our
body.
• Vitamin A is the name of a group of fat-soluble retinoids,
including retinol, retinal, and retinyl esters.
• Two forms of vitamin A are available in the human diet:
preformed vitamin A (retinol and its esterified form, retinyl
ester) and provitamin A carotenoids.
• Vitamin A is an antioxidant.
• It exists naturally in the foods we eat and can also be
consumed through supplements.

3. Forms of Vitamin A
Though vitamin A is often considered a singular nutrient, it’s really
the name for a group of fat-soluble compounds, including retinol,
retinal and retinyl esters.
There are two forms of vitamin A found in food.
• Preformed vitamin A — retinol and retinyl esters — occurs
exclusively in animal products, such as dairy, liver and fish,
• Provitamin A carotenoids are abundant in plant foods like fruits,
vegetables and oils.
• Both provitamin A and preformed vitamin A must be metabolized
intracellularly to retinal and retinoic acid, the active forms of
vitamin A, to support the vitamin’s important biological functions
To use them, our body must convert both forms of vitamin A
to retinal and retinoic acid, the active forms of the vitamin.

4. Functions of Vitamin A
One of the best-known functions of vitamin A is its role in
vision and eye health.
• Retinal, the active form of vitamin A, combines with the
protein opsin to form rhodopsin, a molecule necessary for
color vision and low-light vision.
• It also helps protect and maintain the cornea — the
outermost layer of your eye — and the conjunctiva — a thin
membrane that covers the surface of your eye and inside of
your eyelids.

5. • Vitamin A is critical for vision
• Three light sensitive pigments present in cones are
responsible for colour vision. They are porphyropsin,
iodopsin and cyanopsin.
• All three pigments 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.
• Vitamin A also supports cell growth and differentiation.
• Additionally, vitamin A helps to maintain surface tissues
such as your skin, intestines, lungs, bladder and inner ear.

6. • Vitamin A also acts as an antioxidant. Carotenoids fight free
radicals — highly reactive molecules that can harm your body
by creating oxidative stress
• It supports immune function by supporting the growth and
distribution of T-cells, a type of white blood cell that protects
your body from infection.
• Vitamin A also helps in fetal development.
• Vitamin A also stimulates the production and activity of white
blood cells, takes part in remodeling bone, helps maintain
healthy endothelial cells (those lining the body’s interior
surfaces), and regulates cell growth and division such as
needed for reproduction.

7. VITAMIN A

9. Sources of Vitamin 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

10. 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.

11. sources

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15. Activity.
Q. Which is the leading cause of blindness in children
worldwide.
• (a) Glaucoma
• (b) Cataracts
• (c) Colour blindness
• (d) Vitamin A deficiency
Ans_______________

16. Digestion and 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.
• Because vitamin A is fat soluble, it’s stored in body tissue
for later use.
• Most of the vitamin A in our body is kept in the liver in the
form of retinyl esters.
• These esters are then broken down into all-trans-retinol,
which binds to retinol binding protein (RBP). It then enters
bloodstream, at which point our body can use it.

17. RDA of Vitamin A
• The Recommended Dietary Allowance (RDA) for men and
women is 900 and 700 μg retinol activity equivalents
(RAE)/day, respectively.
• The Tolerable Upper Intake Level (UL) for adults is set at
3,000 μg/day of preformed vitamin A.

18. 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 re
synthesis 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.

19. 2. Growth of bone and formationof tooth are defective.Thick
and long bones are formed.
3. Nerve growth also affected.Degeneration of myelin
sheath occurs.
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.

22. Night blindness

23. Retinopathy

24. Toxicity
• Vitamin A toxicity can be acute (usually due to accidental
ingestion by children) or chronic.
• Both types usually cause headache and increased
intracranial pressure.
• Acute toxicity causes nausea and vomiting.
• Chronic toxicity causes changes in skin, hair, and nails;
abnormal liver test results; and, in a fetus, birth defects.
Diagnosis is usually clinical. Unless birth defects are
present, adjusting the dose almost always leads to
complete recovery.

25. Summary
• Vitamin A is a fat soluble vitamin.
• Vitamin A is important for normal vision, gene expression,
reproduction, embryonic development, growth, and
immune function.
• Preformed vitamin A exists in animal foods like liver,
salmon and egg yolks, while provitamin A carotenoids are
found in plant foods, including sweet potatoes, kale and
cabbage.
• Vitamin A deficiency can lead to blindness, increased
infection risk, pregnancy complications and skin issues.

26. Activity..
Q. Which of the following vitamin functions as both,
hormone and visual pigment?
(a) Thiamine
(b) Retinal
(c) Riboflavin
(d) Folic acid
Ans_______________

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