By Amara Khanam
the science of food and its relationship to health.
Nutrition basically deals with the role played by different nutrients in body growth, development and maintenance.
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NUTRIENTS OR FOOD FACTORS:
the organic and inorganic constituents present in the food with specific functions. There are about 50 different nutrients present in the food we eat. Nutrients are divided into two broad categories:
Macronutrients: they form the main bulk of food and provide energy after metabolism e.g. proteins, carbohydrates and fats.
Micronutrients: they are required by the body in small quantity. Posta They do not provide energy but are essential for the utilization of macronutrients. They are vitamins and minerals.
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VITAMINS (HAYATEEN):
A vitamin may be defined as the organic compound present in different foods which is required for proper utilization of macronutrients and is essential for the growth and maintenance of the body.
Discovery of vitamins started from observation of their deficiency symptoms. The term "vitamin" was suggested by Hopkins in 1912.
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CLASSIFICATION OF VITAMINS:
The fat soluble vitamins:
soluble in fats but insoluble in water.
are absorbed from the alimentary canal with lipids and bile salts are required for their absorption.
transported through blood after binding with carrier proteins.
*not excreted from the body and are stored in liver.
deficiency occurs only when the stores are depleted.
*Over consumption may lead to their toxicity (hypervitaminosis).
*vitamins A, D, E & K belong to this group.
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THE WATER SOLUBLE VITAMINS:
"these vitamins are soluble in water but insoluble in fats.
"Their absorption is simple.
"require no carrier protein for transportation.
"are excreted from the body and generally not stored so toxicity is quiet unlikely and the deficiency manifests rapidly.
-Vitamins B complex & C belong to this group.
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VITAMIN A
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1. Vitamin A/ Anti-xerophthalmia factor/ Retinol/ anti-infective vitamin:
McCollum, Simmonds and Kennedy first isolated vitamin A in 1913. This vitamin prevents against xerophthalmia hence also called as the anti-xerophthalmic factor.
Chemistry: vitamin A is a fat soluble vitamin which exists in three chemical forms- retinal, retinol and retinoic acid. The all-trans retinal form also called as vitamin A, is the most common naturally occurring form while 11-cis retinal (vitamin A2) is the biologically active form. The pro-vitamin beta carotene is present in plant foods which is converted into retinol in intestinal
mucosa.
Absorption: intestine is the major site of absorption of vitamin A. its absorption occurs with fat through lymphatics and requires bile salts. After absorption it is transported to liver and is stored there as retinol palmitate.
Transport: vitamin A is transported from liver to retina, skin, gonads and other tissues as trans retinol after binding with the retinol binding protein RBP.
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Functions:
1. Vitamin A is essential for normal vision. It helps in the production of retinal pigments
needed for vision in dim light. (Wald's visual cycle)
2. It is necessary for maintaining normal structure and function of epithelium which lines
intestinal, respiratory and urinary tracts as well as the skin and eyes.
3. It helps the growth and differentiation of various tissues by regulating gene expression. 4. Helpful in fighting against infections by inducing immune response.
5. Vitamin A is required for normal reproduction.
6. Vitamin A has anti-cancer activity.
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Sources:
a) Animal sources: fish liver oil is the richest source of vitamin A. liver, eggs, butter,
cheese, whole milk and meat are also rich sources of vitamin A.
b) Plant sources: dark green leafy vegetables such as spinach (paalak) and amaranth (chaulai,
saag). Other rich sources are papaya, mango, tomatoes, pumpkin, and carrots etc.
D
c) Fortified foods: foods fortified with vitamin A such as Vanaspati ghee, margarine (butter spread made up of refined vegetable oils) and milk are also important sources of vitamin
A.
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Deficiency of vitamin A
a) Causes:
a) poor dietary intake.
b) Defective intestinal absorption
c) Liver and kidney diseases.
a) Deficiency manifestations:
Xerophthalmia (dryness of eyes)
Bitot's spots (grayish-white triangular plaques on conjunctive at either side of cornea)
i)
Night blindness or Nyctalopa (low vision in dim light)
ii)
iii)
v)
33
iv)
Keratomalacia (softening of cornea)
Preventable blindness (common in Indian children below the age of 5
years)
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vi)
,44༠༡
Phrynoderma/Toad skin (hyperkeratnization and thickening of hair follicles with skin eruptions)
vii) Increased susceptibility to infection may result from vitamin A deficiency.
For this reason, vitamin A is also called as the anti-infective vitamin. viii) Degeneration of intestinal, respiratory and urinary tracts epithelia. ix) Abnormal bone growth
X
Degeneration of nervous system and retina.
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b) Assessment of deficiency:
i)
History taking & Clinical examination
ii)
Dark adaptation test (normal <6.5 mins)
iii)
Serum retinol levels (normal range 30-100mcg/dl).
iv)
Serum RBP levels (normal range 3-6 mg/dl)
v) Liver and kidney function tests.
Hypervitaminosis/toxicity of vitamin A: excess intake of vitamin A can lead to toxicity. Symptoms of toxicity are anorexia, irritability, headache, peeling and yellowish discolouration of skin, drowsiness and vomiting.
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XEROPHTHALMIA
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BITOT'S SPOTS
SARY ROUNDS
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PHRYNODERM
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KARATOMALACIA
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By Amara Khanam
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