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Nutrition

Vitamin A DeficiencyBy

Wendwesen.A.Oct 10-2016

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Definition

Vitamin A is the name given to a group of relatedcompounds that include retinol , retinal , and retinoicacid

Have similar biologic activitiesVitamin A, in the strictest sense, refers to retinolRetinoic acid is its active form

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Sources

Sources of vitamin A can be classified as1. Preformed vitamin A sources:

Contains active vit A Liver, fish, eggs, milk, and butter

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2. ß-Carotene containing sources: Called pro-vitamin A carotenoids It is important compound in the food Has provitamin A activity and efficiently converted to

retinol Yellow and leafy green vegetables such as carrots,

squash, and spinach

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Absorption and Storage

• Vitamin A is a fat-soluble vitamin• Absorption requires bile• Retinol and β-carotene are absorbed in the intestine• 90% of the body's vitamin A reserves are stored in the

liver called ITO cells• Storage lasts at least 6 months• Retinol is transport form & retinol ester is the storage

form

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Physiologic roles of vitanim A

1. Maintenance of normal vision• Retinaldehyde is the essential form of vitamin A that is required for normal vision• The visual process involves four forms of vitamin A

containing pigments: Rhodopsin in the rods, the most light-sensitive pigment3 iodopsins in cone cells each responsive to specific colors in bright light

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2. Cell growth and differentiation• Vitamin A is important in differentiation of mucus-secreting epithelium• When deficient, the epithelium undergoes squamous

metaplasia differentiating into a keratinizing epithelium

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Cont’d...3. Host resistance to infections• Maintain the integrity of the epithelium of the gut• Boots the immune system• Vitamin A supplementation can reduce morbidity and mortality from some forms of diarrhea, and measles• Infections may reduce the bioavailability of vitamin A• By inhibiting retinol binding protein synthesis in the liver

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• Dietary supplements reduce mortality by 20% to 30%• Retinoids are used clinically for the treatment of – skin disorders such as severe acne and certain forms

of psoriasis– acute promyelocytic leukemia !

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Deficiency• Causes of vitamin A deficiency can be:

Chronic dietary deficiency, or Secondary deficiencies: malabsorptions,

• Deficiency states include:1. Ocular manifestatons• The most common clinical presentation• Ocular manifestations f vitamin A is called Xerophthalmia• Night blindness is earliest manifestation of vit A deficiency• Graded accordingly by WHO

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• Xerophthalmia referred to as dry eye• Xerosis conjunctivae there is dryness of the

conjunctiva as the normal lacrimal and mucus-secreting epithelium is replaced by keratinized epithelium

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• Bitot spots build up of keratin debris in small opaque plaques

• Keratomalacia erosion of the roughened corneal surface with softening and destruction of the cornea

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2. Respiratory tractLoss of the mucociliary epithelium of the airways

predisposes to secondary pulmonary infections,3. Urinary system

Desquamation of keratin debris in the urinary tract predisposes to renal and urinary bladder stones

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4. Dermatologic Hyperplasia and hyperkeratinization of the epidermis Plugs the ducts of the adnexal glands may produce follicular or papular dermatosis

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ToxicityDo you know that hypervitaminosis A can mimic brain

Tumor?First noted in Arctic explorers who ate polar bear liver150 mg in adults or 100 mg in children can induce toxic symptoms The symptoms of acute vitamin A toxicity include:

headache, dizziness, vomiting, stupor, and blurred vision