Transcript Vitamin A

Taif University
College of Medicine
Preparatory Year Students
Medical Biochemistry (2)
Level 2
Part VI (Vitamins)
Week 11
Vitamins
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Vitamins are organic nutrients that are requiredin the body
in small amounts.
They can not be synthesized in the body, so they must be
supplied by the diet.
They are essential for biochemical functions which are
required for normal growth, development and maintenance
of life.
They protect against deficiency diseases and reduces the
risk of a number of chronic diseases.
They do not provide energy
The best way to get enough vitamins is to eat a balanced
diet with a variety of foods
How Vitamins Differ from
Carbohydrate, Fat, and Protein
Vitamins
Organic
No Calories
Micronutrients
Foods contain very
small amounts
(milligrams or micrograms)
Same
Differ
Carbs, Fats, Proteins
Organic
Provides Calories
Macronutrients
Foods contain
relatively large
amounts
(grams)
Classification of vitamins
Vitamins
Fat
soluble vitamins
Vitamins A, D, E and K
Water
soluble vitamins
Vitamins B group and C
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Fat soluble vitamins
• Dissolve in lipids (fat-like substances)
• Require bile for absorption.
.directly into the lymphatic system
• Can be stored with other lipids in the fatty tissues
• May be toxic in excessive amounts
• They travel in blood associated with a protein carrier.
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Water soluble vitamins
• Absorbed directly into the blood stream
• Travel freely in blood
• Not stored in the tissues ( except vit. B12)
• Excess is excreted in the urine
• The risk of toxicity is small
Vitamins and Their Functions
 Insert
figure 8.1
Water-soluble vitamins and fat-soluble
vitamins
FAT SOLUBLE
VITAMINS
Vitamin A (Retinol)
* Vitamin A,( retinol, retinal and retinoic acid)
* Each of these compounds are derived from the plant
precursor molecule, β-carotene
Functions of vitamin A For
vision in dim light.
•Acts as an antioxidant (it has anticancer activity).
* Formation of mucous membrane.
* Important for normal growth
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(Night
* Impaired vision, inability to see in dim light
Susceptibility to infections
Vitamin A deficiency
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blindness)
 Food sources
– Vitamin A: only in animal products, i.e., liver, cheese,
butter, milk, eggs
– Beta carotene: in deep yellow and green fruits and
vegetables, i.e., carrots, sweet potato, pumpkin, spinach,
apricots, etc and cereals
RDA recommended Dietary allowance (As RAE=retinol
activity equivalents)
- Women = 700 µg
- Men = 900 µg
- RAE = 1 µg retinol = 6 µg β-carotene
- 1 µg retinol = 3.33 IU
Vitamin D
(1,25-dihydroxycholecalciferol)
The biologically active form of the hormone is 1,25-dihydroxy vitamin D3 ( also termed calcitriol).
Functions
Promotes the absorption and renal reabsorption of calcium
and phosphate
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Deficiencies
~ In children = Rickets (weak, deformed bones)
~ In adults = Osteoporosis loss of calcium from bones
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Food sources
~ Only in animal products, butter, fish, eggs, vitamin-D fortified milk
~ Milk products, i.e., cheese, yogurt, ice cream are not fortified
~ Synthesis under skin in sun light.
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RDA
~ Women/men = 5 µg
~ Over 50 years old = 10 µg
~ Over 70 years old = 15 µg
1,25-dihydroxyvitamin D3
Vitamin E (α-tocopherol)
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Functions
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Vit. E is Antioxidant against peroxidation of
polyunsaturated fatty acids in phospholipids of cellular
and sub-cellular membranes. The first defensive
mechanism
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Antioxidant activity of vit. E is enhanced by selenium.
Deficiencies
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- Neurologic disorder, hemolytic anemia
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Food sources
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~ Oils and fats ~ Whole grains, wheat germ,
Leafy green vegetables, tomatoes -Nuts and seeds
- Eggs
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RDA
~ Women = 15 mg
~ Men = 15 mg
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Vitamin K (K1:Phylloquinone / K2
:menaquinone
K3 is synthetic menadione)
Functions
• Essential component of blood clotting system
• Aids in calcium in corporation in bones
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Deficiencies
~ Bleeding,
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bruises ‫الكدمات‬
Food sources
~ Leafy green vegetables, grain products.
~ It is produced in the gut by bacteria
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RDA
~ Women = 90 µg
~ Men = 120 µg
WATER SOLUBLE
VITAMINS
Most of its functions as components of specific coenzymes
Water soluble vitamins
Vitamin C (Ascorbic Acid)
Functions
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wounds healing-Collagen formation -Fights infections - enhances
immune response -Antioxidant
Helps in iron absorption.
Important for synthesis of steroid hormones and bile acids
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Deficiencies
~ Bleeding- Poor of wound healing
~ Advanced stage = Scurvy, swollen and bleeding gums
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Food sources
~ Fruits: citrus, cantaloupe, strawberry, kiwi, mango, papaya
~Vegetables: broccoli, green and red pepper, collard, tomato, sweet
potato, parsley
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RDA
~ Women = 75 mg
~Men = 90 mg
~ Smokers = 200mg
Thiamin (vitamin B1)
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Functions
~ All cells use thiamin as thiamine pyrophosphate (TPP
coenzyme) to help the body to release energy from
carbohydrates, fats and protein.
~ Helps growth and maintains nerves and muscles
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Deficiencies: (Beriberi)
~ Fatigue, weakness , Nerve disorders , mental confusion
and Heart irregularity.
Beriberi
Food sources
~ Grain products
~ Ready to eat cereals
~ Meats and liver
~ Milk and cheese (low sources)
~ Beans
~ Seeds and nuts
RDA
~ Women = 1.1 mg ~ Men = 1.2 mg
Riboflavin (Vit. B₂)
. Riboflavin is the precursor for the coenzymes, flavin
mononucleotide (FMN) and flavin adenine dinucleotide
(FAD).
•Functions:
~ FMN and FAD serve as coenzymes of oxidoreductase
enzymes involved in oxidation of glucose, fatty acids,
amino acids and α-keto acids.
Deficiencies
~ Cause riboflavinosis.
- skin rash, - dermatitis,
- Cheilosis: fissures at the corner of the mouth
- Glossitis: tongue smooth and purplish
Sources
~ The major source is leafy vegetables. Other good sources are yeast, cauliflower,
liver, eggs and milk.
*RDA:  1.2-1.7 mg/day.
Niacin (B3)
Niacin (nicotinic acid) is also known as vitamin B3.
NAD (Nicotinamide adenine dinucleotide).
•NADP (Nicotinamide adenine dinucleotide phosphate).
Function:
~ NAD and NADP coenzymes are very important in carbohydrate, lipid and
amino acids metabolic pathways.
~ Nicotinic acid helps maintain normal nervous system functions.
~ Nicotinic acid is a vasodilator and has a blood lipid lowering effect (hypolipidemic)
Deficiencies (Pellagra) ~
Skin disorders- Nervous and mental disorders
~ Diarrhea, indigestion- Fatigue
Food sources
~ Same as for thiamin
~ Tryptophan (an essential amino acid) is a precursor of niacin
(1mg of nicotinic acid formed from 60 mg tryptophan)
RDA
~ Women = 14 mg Men = 16 mg
Pantothenic acid (vitamin B₅)
Pantothenic acid is also known as vitamin B5.
•Functions:
•Pantothenic acid is a part of the coenzyme A (Co A or Co A-SH)
which acts as acyl carrier in many enzymatic reactions involved in
energy metabolism.
•Deficiency: Because of the widespread occurrence of
pantothenic in natural food, dietary deficiency is unlikely
in the human.
* Food sources:
Yeast, legumes, whole grain cereals, beans, liver, meat,
* RDA: 5 – 10 mg / day.
egg, milk
Vitamin B₆
* Vitamin B₆ consists of 3 derivatives:
pyridoxine, pyridoxal and pyridoxamine.
• All three compounds are efficiently converted
to the biologically
Pyridoxal Phosphate
active form of vitamin B₆ pyridoxal phosphate
*Functions:
• Pyridoxal phosphate (PLP or Pyr.P) is the active form and is a
coenzyme in many reactions of amino acid metabolism.
Deficiencies: neurologic disease
Food sources:
Liver, meat, mackerel, egg, banana, corn, wheat, royal jelly of bees.
* RDA
Adult 2 mg
Infant and children 0.5 – 1.5 mg/ day
Pregnant and lactating women 2.5 mg/ day
Biotin – B7 (Vit. H)
* Function:
~ It is important in energy metabolism.
~ Involved in carboxylation reactions i.e. carrier CO₂:
• acetyl CoA carboxylase in FA synthesis
• pyruvate carboxylase in gluconeogenesis
• propionyl-CoA carboxylase.
* Food sources:
• Widely distributed in nature
• It can be synthesized by intestinal flora.
* RDA : 150 – 300 ug / day.
* Deficiencies: widespread injury is rare but may
be induced by eating large amounts of raw egg
white that contain protein avidin which combine
with biotin preventing its absorption (dermatitis,glositis, nausea)
Folic Acid(Folate-B9)
Dihydrofolate (DHF) & tetrahydrofolate (THF)
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Functions
~ It is required for formation of all new cells(cell division)
~ Promotes the normal formation of red blood cells.
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Deficiencies - anemia
~ Growth failure
~ Increased risk of heart disease & stroke
~ Megaloblastic anemia ( due to inhibition of DNA synthesis)
 Food sources
~ Leafy vegetables: Spinach, collard, romaine, broccoli
~ Fruits, milk, liver, dried beans, bread, enriched cereals
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RDA
~Women/men = 400 µg (micrograms)
~Pregnant women = 800 µg
Vitamin B12 (Cobalamin)
Functions
~ Helps maintain nerve tissues
~ Needed for normal red blood
cell development with the help
of folate
Vitamin B12 (cobalamin)
Deficiencies: Pernicious anemia
~ Neurological disorders
(nervousness, tingling sensations,brain degeneration)
~ Fatigue
Food sources
~ Liver, eggs, oysters, shrimp, meat, chicken and milk.
~ Not found in plant foods.
*RDA  Women and men = 2.4 µg
Pregnant and lactating women = 6 µg
SUMMARY
Summary: Fat-Soluble Vitamins
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Table 8.2
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Figure 8.6
MyPyramid: Fat-Soluble Vitamins
Water-Soluble Vitamins
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Insert Figure 8.17
MyPyramid and the Water-Soluble Vitamins
Vitamins and Metabolism
Home work
What are the different
names and main function
for vitamins A, B1, B2, B3,
B5, B6, B9B12, C,D,E and K?
What are the most likely
diseases produced as a result
of deficiencies of vitamins A,
B1, B2, B3, B5, B6, B9B12, C,D,E
and K?
Thank you for
listening
Best wishes for
success