Fat Soluble Vitamins PDF

Fat soluble vitamins Dr. Salah Omar December 10, 2024 www.gmu.ac.ae COLLEGE OF Learning objectives: Define Vitamins Describe their general characteristics and functions Differentiate between fat and water soluble vitami...

Fat soluble vitamins Dr. Salah Omar December 10, 2024 www.gmu.ac.ae COLLEGE OF Learning objectives: Define Vitamins Describe their general characteristics and functions Differentiate between fat and water soluble vitamins List the names of the fat soluble vitamins Describe synthesis and activation of Vitamin D in the body Explain the roles of the fat soluble vitamins A, D, E and K in the body Describe diseases associated with deficiency of Vitamins A, D and K. DEFINITION: Vitamins are a group of organic nutrients that are:  needed in very small quantities  cannot be synthesized by the body  Necessary for metabolism, growth, reproduction, and for the maintenance of tissue.  Water soluble (B&C) Fat soluble (A, D, E, K)  Transported free in the  Absorbed and transported blood like lipids (bound to proteins)  Stored mostly in the liver  Not stored to any great extent  Manifestation of deficiencies  Manifestation of is slower deficiencies is fast  Excess not excreted, toxic  Excesses are excreted and levels are likely to develop. so unlikely to reach toxic  Required periodically levels  Required in frequent small doses  VITAMIN A STRUCTURE: 3 Active forms (Retinol, Retinal and Retinoic acid) are found in animal tissues and they are collectively known as retinoids. Carotenoids (from plants) function as provitamins and can be cleaved (cut) to form retinol. ABSORPTION / TRANSPORT Dietary beta carotene is converted to retinol. Bile and dietary fat are required for absorption Stored in the liver and adipose tissue Role in Metabolism 1. Vision: according to Walds’s visual cycle, cis Retinal is regenerated by isomerisation, completing the visual cycle 2. Retinoic acid and retinol: Behave like steroid hormones. Regulate Epithelial cell growth and differentiation. 3. Retinol: Maintenance of reproduction. 4. Carotenoids function as antioxidants and may reduce the risk of cancer. Sources Preformed vitamin A is found in foods of animal origin like liver, fish , eggs , dairy products. Plants contain provitamin A-carotenoids which can be converted to retinol (Carrots, spinach, broccoli and other dark green/yellow vegetables and fruits). DEFICIENCY Defective night vision (Nyctalopia) Severe deficiency : Xerophthalmia: Drying of the conjunctiva and cornea. Keratomalacia resulting in blindness  TOXICITY  If large amounts of preformed vitamin A or vitamin supplements are taken over months or years it can be toxic.  Pregnant woman should not take excess Vit.A : It can cause congenital malformations in the developing fetus.  Vitamin D (Calciferol) Forms D2 (Ergocalciferol) found in plants D3 (Cholecalciferol) found in animal tissues. Synthesis in the body With the aid of UV light 7- Dehydrocholesterol in the skin can be converted to Cholecalciferol.  Activation: Cholecalciferol undergoes activation in two steps:  25-hydroxylation in the liver.  1α-hydroxylation in the kidney. The final active form of Vitamin D is:  1, 25 Dihydroxycholecalciferol also called Calcitriol  Role of Vitamin D 1. Intestinal mucosal cells:  vitamin D promotes formation of a protein Calbindin which absorbs calcium and phosphorus at the intestinal villi. 2. Increases reabsorption of Ca and phosphorous in kidney tubules Net effect Calcium levels increase and bone growth supported Growing children need more than adults Food sources: Egg yolks, fatty fish and fish liver oils, butter, fortified milk and liver. Causes of vitamin D deficiency: Dietary deficiency. Not exposed to sunlight Due to malabsorption of vitamin D or fat Abnormality of Vitamin D activation due to liver or kidney disease  Deficiency 1. Vitamin D deficiency in children causes rickets (can also be due to deficiency of calcium or phosphorus). Weak, soft, bent bones (bow legs, knock knees, pigeon chest, rickety rosary, bossing of frontal bones ) due to very little mineralization resulting in growth retardation. 2. Vitamin D deficiency disease in adults is called Osteomalacia. Causes increased susceptibility to fractures. Toxicity People taking supplements for a long time. Calcium deposits in soft tissues, e.g. hardening of the arteries and kidney stones.  Vitamin E (Tocopherols) Role is as an Antioxidant: Vitamin E inactivates reactive oxygen species like Superoxide, peroxide, hydroxyl radicals So it protects lipids, membranes and DNA from oxidative damage by these reactive oxygen species and free radicals.  Food sources o Nuts and peanuts o Plant oils like sunflower, safflower, corn , soybean, o Wheat germ oils. o It is destroyed by cooking and freezing.  Vitamin E is stored in adipose tissue in the body.  Deficiency - Rare, Associated with diseases of fat malabsorption  Vitamin K Forms:  Vitamin K1 (Phylloquinone): found in Green vegetables.  Vitamin K2 (Multiprenylmenaquinone): synthesized by intestinal bacteria.  Vitamin K3 (Menadione): synthetic, water soluble form.  Role of Vitamin K  Blood clotting ( Coagulation) – Vit.K act as a coenzyme.  Clotting factors: (II, VII, IX&X ) become active after undergoing Vitamin K dependent carboxylation Anticlotting drugs: Warfarin, Dicumarol exert anticoagulant effects by inhibiting the maturation of Vit. K dependent blood clotting proteins.  Food sources:  Normally present Bacteria in the small intestine synthesize vitamin K  Green leafy vegetables (spinach, asparagus), cabbage family, carrots, liver, egg also contain Vitamin K  Deficiency - rare in adults  Long term antibiotic treatment, fat malabsorption may cause deficiency. Symptoms: Easy bruising and bleeding from minor injuries. Clotting is delayed. Deficiency in the newborn baby can occur since  Newborn infants have a sterile GI tract.  liver stores of vitamin K are too low  Human milk is also low in Vitamin K. So most infants (especially premature) are given Vitamin K (1mg) injection at birth to prevent hemorrhagic diseases.  Summary Vitamins are organic compounds needed in small quantities in our diet They function mainly as coenzymes They can be classified as fat and water soluble based on properties Fat soluble vitamins are stored in the body, can be toxic if taken in large amounts A, D, E and K are fat soluble vitamins 12/10/2024 22  Summary contd Vitamin A plays a main role in vision, deficiency leads to night blindness and later to blindness Vitamin D plays a main role in calcium absorption, deficiency causes rickets and osteomalacia Vitamin E is an antioxidant Vitamin K plays an important role in maturation of clotting factors, deficiency leads to poor clotting 12/10/2024 23