Vitamins are organic compounds occuringin natural food either as such or asutilizable Precursors which are requiredby the body in trace ammounts to performspecific cellular functions like growth andreproduction.
Vitamins are different from other food stuffs, Donot enter into tissue structure like proteins. Donot undergo degradation to provide energy like carbohydrates and lipids.
Vitamins are categorized based on their solubility:3. Water soluble vitamins5. Lipid (Fat) soluble vitamins
Water soluble Fat soluble vitamins•Polar and •Apolar andhydrophilic hydrophobic •Isoprene derivatives•Hetrogenous except vit.D which is sterol derivative. •Fat soluble,absorbed•Water soluble, along with fats.absorbed along withwater. •TPT along with•Donot require lipoproteins orspecific binding specific bindingproteins for transport. proteins.
•Excreted in the •Not readily excretedurine. in the urine but via bile. •Stored in liver and•Not stored in the adipose tissue.body thereforerequired daily. •Excess can be toxic•Non toxic •Vit.K act as•Act as coenzymes coenzyme,D and A are more like a hormone in function.E is
Vitamin A (retinoids) is essential for growth,reproduction,vision and maintenance ofepithelial tissues.
Preformed vitamin A Retinoids (retinal, retinol, retinoic acid) Found in animal products Provitamin A Carotenoids Must be converted to retinoid form Intestinal cells can split carotene in two (molecules of retinoids) Found in plant products
Vitamin A in Foods Preformed(Retinoids) Liver, fish oils, fortified milk, eggs, other fortified foods Provitamin A (carotenoids) Dark leafy green, yellow-orange vegetables/fruits
RECOMMENDED DIETARY ALLOWANCE(RDA) 1000 Retinol equavelents for males and 800 RE for females.1 Retinol equavalent = I μg of retinol,6 μ g of ß carotene or 12 μ g of other carotenoids.
FUNCTIONS OF Vit.AVISUAL CYCLE Rhodopsin,the visual pigment of the rod cells in the retina,consists of 11-Cis retinal specifically bound to protein opsin.
Growth and Differentiation of Cells• Retinoic acid is necessary for cellular differentiation• Important for embryo development, gene expression• Retinoic acid influences production, structure, and function of epithelial cells that line the outside (skin) and external passages (mucus forming cells) within the body.
GROWTH AND REPRODUCTION Retinol and Retinal are essential for normal reproduction,supporting spermatogenesis in male and preventing fetal resorption in females.
ACNE AND PSORIASIS Retinoic acid and its derivatives are used to treat acne. Mild acne is topically treated with Tretinoin. Severe acne is treated with Isotretinoin ,administered orally.
Prevention of chronic diseases β Carotene decreases the incidence of lung and skin cancer. β Carotene functions as an antioxidant.
Consequences: Night blindness Decreased mucus production Decreased immunity Bacterial invasion of the eye Conjunctival xerosis Bitot’s spots Xerophthalmia Irreversible blindness Follicular hyperkeratosis Poor growth
Toxicity of Vitamin A Acute – short-term megadose (amounts exceeding 7.5mg/day); symptoms disappear when intake stops GI effects Headaches Blurred vision
Teratogenic (may occur with as little as 3 x RDA of preformed vitamin A) Tends to produce physical defect on developing fetus as a result of excess vitamin A intake Spontaneous abortion Birth defects