Vitamins Lecture 4 PDF

Vitamins Faculty of Applied Medical Sciences Introduction to Biochemistry First Year Second Semester Aims of the Lecture Definition Fat soluble Vitamins Water soluble Vitamins What are Vitamins? Vitamins are organic substances needed for normal cell function, g...

Vitamins Faculty of Applied Medical Sciences Introduction to Biochemistry First Year Second Semester Aims of the Lecture Definition Fat soluble Vitamins Water soluble Vitamins What are Vitamins? Vitamins are organic substances needed for normal cell function, growth, and development. This means that these vitamins are required for the body to work properly. Vitamins are required in µg to mg quantities per day (micronutrients) Vitamins Classification Vitamins are classified as fat-soluble or water-soluble Fat-soluble vitamins (A, D, E, and K) dissolve in fat and tend to accumulate in the body. Water-soluble vitamins (vitamin C and the B-complex vitamins) must dissolve in water before the body can absorb them; therefore, they cannot be stored. Any water-soluble vitamins unused by the body are primarily lost through urine.  1. Vitamin A (Retinoids) Vitamin A exists in several forms, including alcohols (retinol), aldehydes (retinals), and retinoic acid. The body can convert β-carotene and other carotenoids to retinol  Vitamin A Functions 1. Vision 2. Reproduction 3. Growth 4. Stabilisation of cellular membranes  Vitamin A Deficiency Rare as it can be found in animal liver Deficiency may occur due to fat malabsorption Vitamin A deficiency can cause vision loss and blindness. It can also lead to complications in skin, heart, lungs, tissues and immune system Vitamin A Excess Hypervitaminosis A: Acute toxicity from a single massive dose leads to abdominal pain, nausea, vomiting, severe headaches, dizziness, sluggishness, and irritability, followed within a few days by desquamation of the skin and finally recovery Chronic toxicity from moderately high doses is characterized by joint and bone pain, hair loss, dryness and fissures of the lips, anorexia, benign intracranial hypertension, weight loss, and hepatomegaly Carotenaemia Carotenemia: Reversible yellowing of skin Does not cause toxicity as its metabolic conversion is regulated by vitamin A status 8  2. Vitamin D (Calciferols) Vitamin D is a group of fat-soluble vitamins from the food we eat and hormones that our body makes. It is responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and for many other biological effects Vitamin D Functions Regulation of Calcium and Phosphate: 1. Increases intestinal absorption of Calcium 2. Resorption and formation of bone, via Parathyroid hormone (PTH) 3. Reduces renal excretion of Calcium  Vitamin D Deficiency Rickets in Children Osteomalacia in Adults 3. Vitamin E (Tocopherols) Important antioxidant, preventing oxidative damage to cell membranes Stored in tissues especially adipose tissue ANd9GcTwJxanC6J5kuIwzqJ-8G12YVEJgLEJZRXV4yrejwCZNeGXEC8Nt5hQDsc ANd9GcQ0U7Qvb2E5-_X7YWV6rp1uTmJ5figSRlljl5u3BG9KlHAhMGOONl3vpV0 ANd9GcTzHAzqn3DAFkKBp28ZQZUFfHE7uhO_lnjD5AfamqoJ4rsteNszXPYc_Eo ANd9GcTa92-q4hWQcY05P_72l-W0-aCqZcAa85qTtwMrhiKZIv6gGkAYBd0TmOc Vitamin E Deficiency Deficiencies in mainly 3 groups: Fat malabsorption e.g. Cystic Fibrosis Premature, very low birth weight infants Rare congenital disorders of fat metabolism e.g. Abetalipoproteinemia Can result in: Haemolytic anaemia due to the shortened lifespan of erythrocytes with fragile membranes which not respond to iron therapy Myopathy Retinopathy Neuropathy Vitamin E Excess Low toxicity High intakes may impair absorption of other fat-soluble vitamins It can, therefore, result in vitamin K deficiency and consequently bleeding problems  4. Vitamin K Promotes blood clotting and is required for the conversion of several clotting factors and prothrombin. Necessary for liver synthesis of plasma clotting factors II, VII, IX and X. Vitamin K Sources Vitamin K1 (phylloquinone) Synthesized by plants and present in food Vitamin K2 (menaquinone) Synthesized in humans by intestinal bacteria Synthetic vitamin K’s: K3 (menadione) K4 (menadiol)  Vitamin K Deficiency Rare in adults Bleeding can occur. Newborn infants may be deficient Haemorrhagic disease of the newborn develops readily as intestinal flora have not become established within the first week of birth and early breast milk is low in vitamin K.  Vitamin K Excess Vitamin K1 is relatively safe and up to 1mg/day unlikely to result in adverse effects Synthetic forms, particularly water-soluble Vitamin K3 (menadione) are more toxic High doses result in oxidative damage, red cell fragility, and formation of methaemoglobin In premature infants, this has caused liver problems and brain damage Water Soluble Vitamins Vitamin C Vitamin B (complex) 5. Vitamin C Adults need 40 mg/day. Higher requirements in: Diets devoid of fresh fruits and vegetables Smokers, Pregnancy, post-operative patients Vitamin C - Function 1. Collagen Synthesis 2. Antioxidant 3. Iron absorption: Facilitates intestinal absorption of dietary non-haem Fe by keeping it in the Fe2+ state Vitamin C Deficiency Scurvy Easy bruising and bleeding, teeth, and gum disease, hair loss Scurvy is treated with vitamin C supplements, which can quickly improve your symptoms Some symptoms, such as joint pain, will usually resolve within 48 hours Most people will make a full recovery within two weeks  6. Vitamin B1 (Thiamine) Occurs in the body as free form, monophosphate (TMP), triphosphate (TTP), and pyrophosphate (TPP). Coenzyme for a small number of enzymes that are critical in the production of energy from nutrients: Transketolase - pentose phosphate pathway, leading to ribose-5- phosphate - needed for DNA, RNA, ATP, GTP Pyruvate dehydrogenase - forms acetyl CoA α-ketoglutarate dehydrogenase - forms succinyl CoA  Thiamine Deficiency They include fatigue, irritability, poor memory, loss of appetite, sleep disturbances, abdominal discomfort, and weight loss. Eventually, a severe thiamin deficiency (beriberi) may develop, characterized by nerve, heart, and brain abnormalities.  7. Vitamin B2 (Riboflavin) Important in: Energy production Carbohydrate, fat, and protein metabolism Formation of antibodies and red blood cells It is the central component of the cofactor (FAD). Deficiency: Rarely Symptoms include sore throat, sore tongue, sore mouth, sore corners of lips. 8. Vitamin B3 (Niacin) Also known as nicotinic acid Function: Used to make NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate) Act as coenzymes to more than 200 enzymes which are involved in redox reactions Deficiency (Pellagra) Diarrhoea Dementia Dermatitis 9. Vitamin B6 Pyridoxine/Pyridoxal/Pyridoxamine Pyridoxal-5’-phosphate cofactor for amino acid metabolism: transamination, deamination, and decarboxylation Conversion of tryptophan to niacin Release of glucose from glycogen, haem synthesis Causes of deficiency Inadequate intake Pyridoxine-inactivating drugs (e.g. anticonvulsants, isoniazid)  10. Vitamin B12 (Cobalamin) Released from food by acid and enzymes in the stomach, so that it can bind to proteins Pancreatic enzymes degrade proteins, leaving vitamin B12 free to bind to the intrinsic factor (IF), secreted by the stomach. In the small intestine, receptors take up the vit B12-IF complex in the presence of calcium supplied by the pancreas 1% of vitamin B12 can be absorbed passively Vitamin B12 Deficiency Pernicious anaemia: autoimmune destruction of IF-producing cells in stomach. Malabsorption: lack of stomach acid and pancreatic disease; resulting in neurologic symptoms.  11. Folate Coenzyme in methylation reactions and DNA synthesis. Many foods are fortified with folic acid Higher requirements during pregnancy  Folate Deficiency ▪ Causes: Malabsorption Use of drugs that interfere with folic acid metabolism Disease states which increase cell turnover (leukaemia, haemolytic anaemias) ▪ Symptoms ↑ cardiovascular disease risk Macrocytic anaemia - which can lead to lethargy and weakness Foetal developmental abnormities  12. Biotin Required for cell growth, fat and amino acid metabolism Cofactor for carbon dioxide transfer in several carboxylase enzymes Deficiency rare as gut flora produce biotin in excess of daily requirements Number of metabolic disorders where problems with biotin use Any Questions?