These are potent organic compounds which
are not synthesized inside the body but are
essential for the maintenance of metabolic
processes at normal level, for the normal
growth & health.
They required in very small amounts as they
act as co-enzymes.
An absence of any of the vitamins in the diet
may result in the development of a deficiency
disease such as: beriberi, scurvy etc.
Certain compounds which are converted to
vitamins on hydrolysis or by activation with
some physical factors such as radiation. They
are called provitamins.
β-carotene – converted to vitamin A in the
Cholesterol – converted to vitamin D by
Vitamins with the same physiological action
are called vitamers or isotels.
Examples: Different isotels of vitamin D are
D2, D3 and vitamin A are A1, A2.
Some substances which have vitamin like
actions & functions but they are not classified
as vitamins, called smaller mites.
Vitamins have been classified on the basis of
their solubility. There are two common
The fat soluble vitamins and water soluble
Fat soluble vitamins – vitamin A, D, E & K.
Water soluble vitamins – vitamin B-complex
& vitamin C.
Fat soluble vitamins
Vitamin A (Retinol)
The retinoids, a family of molecules that are
related to retinol (vitamin A), are essential for
vision, reproduction, growth, and maintenance
of epithelial tissues.
Retinoic acid, derived from oxidation of
dietary retinol, mediates most of the actions of
the retinoids, except for vision which depends
on retinal, the aldehyde derivative of retinol.
Structure of vitamin A
Vitamin A is often used as collective term for
several related biological active molecules.
1- Retinol (C20H29OH): A primary alcohol
containing a β-ionone ring with an unsaturated
side chain, retinol is found in animal tissues
as a retinyl ester with long-chain fatty acids.
2- Retinal: This is the aldehyde derived from
the oxidation of retinol. Retinal & retinol can
readily be interconverted.
3- Retinoic acid: This is the acid derived from
the oxidation of retinal. Retinoic acid cannot
be reduced in the body, and, therefore, can not
give rise to either retinal or retinol.
4- β-carotene: Plant foods contain β-carotene,
which can be oxidatively cleaved in the
intestine to yield two molecules of retinal. In
humans, the conversion is inefficient.
Vitamin A naturally occurs in the animal
tissues. It is found in high conc in fish liver
oils especially in cod liver oil, which is the
most important source therapeutically.
Kidney, cream, butter, and egg yolk are good
source of preformed vitamin A.
Another important source is the plants, which
contain carotenoids, β-carotene is a yellow
pigment contained in corn, sweet potatoes,
carrots, tomatoes, apricots, yellow peaches etc.
Per day vit A is required in international unit
of carotene from 5000 to 6000.
In pregnancy this is required up to 8000 I.U.
Functions – deficiency of vit A
Night blindness is one of the earliest signs of
vit A deficiency. Prolonged deficiency leads to
an irreversible loss in the number of visual
Severe vit A deficiency leads to
xerophthalmia, a pathological dryness of the
conjuctiva & cornea. If untreated, results in
corneal ulceration &, ultimately blindness
because of the formation of opaque scar tissue.
Acne & psoriasis: due to the deficiency of vit
A causes changes in the skin, that leads to skin
lesions & acne-vulgaris.
Reproduction: Vit A deficiency leads to the
failure of reproduction. Males become sterile.
Females although deficient are able to
conceive, the babies are unable to survive
due to placental defects.
Urolithiasis: A condition in which urinary
calculous are present. Vit A and an acid ester
diet are effective in dissolving calculi (calcium
Excess of vitamin A intake may lead to
skeletal decalcification (chronic cases),
tenderness over long bones, headache,
nausea, vomiting & drowsiness supposedly
related to the increased spinal fluid pressure
due to tendency of vit A to disrupt biological
A dose of 25,000 to 50,000 IU in children &
over 100,000 in adults may cause severe
Pregnant women particularly should not ingest
excessive quantities of vit A because of its
potential for causing congenital
Anorexia may also develop due to
Vitamin D group belongs to steroids. They
contain perhydrophenantherene cyclopentane
ring as the basic frame work of the molecule.
They are sterols or activated sterols & are
formed from certain sterols as a result of
certain irradiations with sunlight.
Also called anti-Ricket factor, because, it
prevents & cure Ricket.
Chemistry of vit D
Two types of vitamin D.
1- Vitamin D2
2- Viamin D3
1 – Vitamin D2
Vitamin D2 is the activated product of
Ergosterol (provitamin) which is found only in
The UV rays act on ergosterol & open the ring
“B” to produce vitamin D2.
2 – Vitamin D3
The provitamin of D3 is the 7Dehydrocholesterol which is present at the
surface of skin.
It is activated by ultraviolet radiation of sun to
form vitamin D3 by opening the ring “B”.
Vitamin D is present in cows milk & other
milk in very small amount.
It is also present in small amount in butter.
The sterols (provitamin) are present in milk &
vegetable oils and are irradiated to the vit D by
Richest source of vit D are fish liver oil. Cod
liver oil, halibut liver oil & tuna liver oil are
prescribed as a remedy for deficiency disease.
Physiological actions & functions
Vitamin D is essential for the normal growth
of mammals. This is related to the absorption
& utilization of calcium & phosphorus in the
Vit D increases calcium & phosphorus
absorption from small intestine.
It helps in the development & proper growth
of bones & teeth.
It also has a general effect on the metabolism
of citric acid.
It has been observed that vit D increases the
activity of the enzyme phytase. The enzyme
hydrolyses the food phytic acid yielding
It also influence the activity of parathyroid h.
Adults normally have little or no requirements
of vit D. They need vit D during calcium
deficiency & in certain other disorders-200 IU
The infants require 400 IU & the same is
needed during pregnancy & lactation.
Deficiency (hypovitaminosis) of vit D
Nutritional rickets: Vit D deficiency causes a
net demineralization of bone resulting in
rickets in children & osteomalacia in adults.
Rickets is characterized by the continued
formation of the collagen matrix of bone, but
incomplete mineralization, resulting in soft,
In osteomalacia, demineralization of preexisting bones increases their susceptibility to
Hypoparathyroidism: Lack of parathyroid
hormones causes hypocalcemia. These patients
may be treated with calcitriol and calcium
Toxicity of vitamin D (hypervitaminosis)
Like all fat-soluble vitamins, vitamin D can be
stored in the body and is slowly metabolized.
High doses can cause loss of appetite, nausea
Enhanced calcium absorption & bone
resorption results in hypercalcemia, which can
leads to deposit calcium in many organs
(arteries & kidneys).
Beriberi = a degenerative disease of the nerves caused by a deficiency of
the thiamine and marked by pain, inability to move, and swelling
Scurvy = a disease caused by insufficient vitamin C, the symptoms of which
include spongy gums, loosening of the teeth, and bleeding into the skin and mucous
Rickets = bone-softening disease: a disease, especially of children, caused by a
deficiency in vitamin D