Water Soluble Vitamins: B Group Vitamins PDF

WATER SOLUBLE VITAMINS  B Group Vitamins Originally thought to be a single vitamin but now understood to be multiple vitamins – all of which form coenzymes Named in order of discovery but some were later found to be produced by the body and so are no longer classiGed as vitamins (e....

WATER SOLUBLE VITAMINS  B Group Vitamins Originally thought to be a single vitamin but now understood to be multiple vitamins – all of which form coenzymes Named in order of discovery but some were later found to be produced by the body and so are no longer classiGed as vitamins (e.g. B4, B8, B10, B11) Classed together as they found in similar foods though diQerences in structure and function exist Some can be synthesised within the body by B intestinal Sora (note: this is diQerent to being Vitamin B1 Name: Vitamin B1 [A.K.A. thiamine] Structure: Sources: Found in cells therefore present in all whole B natural foods e.g. whole cereal grains, beans, fruits and yeast Vitamin B1 Coenzyme produced: Thiamine pyrophosphate (TPP) Function: Coenzyme to several enzymes in carbohydrate metabolism pathways (helping to release energy from food) B Also involved in conduction of action potentials in neurons and neuro-muscular transmission Vitamin B1 De:ciency state Prevalent in eastern Asia (white rice contains little thiamine) and in chronic alcoholics (severely malnourished). Athletes and pregnant/lactating women may require supplements (increased carbohydrate consumption) 1. Beriberi can aQect diQerent organ systems a. Wet beriberi aQects the cardiovascular system and presents with cardiac failure, dyspnoea and oedema b. Dry beriberi aQects the peripheral nervous system and presents with peripheral neuritis, paralysis and wastage. A severe form of dry B beriberi is known as Wernicke–KorsakoQ syndrome and is characterised by paralysis of  B Vitamin B1 Vitamin B2 Name: Vitamin B2 [A.K.A. riboSavin] Structure: Sources: B Dairy products, eggs, green vegetables and almonds Vitamin B2 Coenzymes produced: Flavin Flavin B mononucleoti adenine de (FMN) dinucleotid Vitamin B2 Function: Heterocyclic system acts as a H acceptor (or donor) R R H Me N N O Me N N O NH NH Me N Me N O H O FAD FADH2 Coenzymes act as prosthetic groups on a family of mainly oxidoreductase enzymes known as Savoproteins Involved in the metabolism of fats, carbohydrates B and proteins Also acts as a coenzyme in the processing of other Vitamin B2 De:ciency state Rare in developed countries due to fortiGed foods but common in developing countries (due to malnutrition) Symptoms include inSammation of the mouth and lips (stomatitis) which is similar to pellagra but without the widespread skin lesions (pellagra sine pellagra) It can also reduce iron absorption leading to anaemia with the size and haemoglobin content of red blood cells remaining normal (normochromic normocytic anaemia) B Vitamin B3 Name: Vitamin B3 [A.K.A. nicotinamide (niacinamide); niacin (nicotinic acid)] Structure: Nicotinamide Niacin Sources: Meat, Gsh and nuts Nicotinamide also used in acne treatments (see B PH1122 RTS) Vitamin B3 Coenzymes produced: Nicotinamide adenine Nicotinamide adenine dinucleotide phosphate dinucleotide (NAD) (NADP) B Vitamin B3 Function: Important in oxidoreductase enzyme reactions: NAD(P)+ is an oxidising agent whilst NAD(P)H is a reducing agent NADPH is important in anabolic processes (e.g. lipid and nucleic acid synthesis) whilst NAD+ is vital to catabolic processes (e.g. metabolism of energy sources like fatty acids and glucose) B Vitamin B3 De:ciency state Body not entirely dependant on dietary intake as nicotinic acid can be produced from dietary tryptophan in vivo DeGciency common in areas in which maize is the principal foodstuQ (as it is low in both nicotinic acid and tryptophan) Pellagra – characterised by ‘dermatitis, diarrhoea and dementia’. Chronic alcoholics also at risk of deGciency Toxicity state Skin Sushes, liver damage (mainly seen B with niacin supplementation; nicotinamide may be given as Vitamin B5 Name: Vitamin B5 [A.K.A. pantothenic acid] Structure: Sources: Dairy products, eggs, avocado, mushrooms Present in the outer layers of whole grains- B milling greatly reduces the pantothenic acid content Vitamin B5 Coenzyme produced: coenzyme A Function: Coenzyme in the synthesis and oxidation of fatty acids Involved in the oxidation of pyruvate as part of the Krebs cycle De:ciency state B Extremely rare and as a result has not been studied thoroughly End of Part 2  Name: Vitamin B6 [A.K.A. pyridoxine, pyridoxal, pyridoxamine] Vitamin B6 Structures: pyridoxine pyridoxal pyridoxamine Sources: Found in most foods of vegetable (pyridoxine) or animal (pyridoxal, pyridoxamine) origin B Interconvertible via their phosphates in vivo Vitamin B6 Coenzyme produced: pyridoxal-5’-phosphate Function: Involved in tryptophan metabolism (vitamin B 6 deHciency is a risk factor for vitamin B 3 deHciency) Also involved in the production of a number of neurotransmitters (e.g. dopamine, GABA) B Acts as a coenzyme for an extremely broad range of enzymes (approximately 4% of enzymes; >140 Vitamin B6 De7ciency state Rare as most diets contain adequate amounts and some is synthesised by intestinal Uora Results in disorders of CNS, skin and mucous membranes Patients taking medicines such as isoniazid may beneHt from increased intake due to increased excretion of pyridoxine Toxicity state Supplementation with high doses of vitamin B6 can lead to nerve damage (particularly in spinal ganglia) which manifests as pain/numbness in B the extremities or in extreme cases di\culty with motor functions Vitamin B7 Name: Vitamin B7 [A.K.A. biotin] Structure: Sources: Egg, avocado, yeast, fresh vegetables B Vitamin B7 Coenzyme produced: N/A [biotin acts as a coenzyme] Function: Required by several carboxylase enzymes that are involved in fatty acid synthesis, amino acid breakdown and glucose synthesis (gluconeogenesis) De7ciency state(s) Rare – severe deHciency never reported in healthy individuals eating a normal mixed diet Presents with thinning hair, brittle nails, rashes and neurological symptoms Pregnant/lactating women at risk of deHciency (clinical reason unknown) B Those eating lots of raw eggs are at risk due to avidin in the whites reducing the absorption of biotin Vitamin B9 Name: Vitamin B9 [A.K.A. folic acid] Structure: Sources: Nuts, seeds, chickpeas, green vegetables Folic acid is the vitamin that is most commonly B added to ‘fortiHed’ foods such as Uour Vitamin B9 Coenzyme produced: tetrahydrofolate (THF) Function: THF is the coenzyme in enzymatic reactions that transfer hydroxymethyl (-CH2OH), formyl (-CHO) and methyl (-CH3) groups in a large number of reactions and signiHcantly in the synthesis of amino B acids and purine/pyrimidine bases in the formation of DNA Vitamin B9 De7ciency state Patients with malignant disease or who are pregnant/breastfeeding are at risk of deHciency due to increased folic acid demand. A number of medications (e.g. methotrexate) interfere with folic acid processing and so create a risk of deHciency Folic acid deHciency during pregnancy is associated with low birth weight, premature birth and neural tube defects Supplements are therefore given in pregnancy, leukaemia and drug-induced folate deHciency DeHciency can cause megaloblastic anaemia (large red blood cells) due to faulty erythrocyte multiplication and B maturation Vitamin B12 Name: Vitamin B12 [A.K.A. cobalamin] Structure: When R = 5’-deoxyadenosyl: adenosylcobalamin CH3: methylcobalamin OH: hydroxocobalamin CN: cyanocobalamin B  Sources: Vitamin B12 Animal food sources (meat, Hsh, milk, eggs) Rare in common plant-based foods (some in fermented foods and seaweed) Coenzyme produced: adenosylcobalamin and methylcobalamin (the body converts hydroxocobalamin and cyanocobalamin from the diet into these active forms) Function: Acts as a cofactor for methionine synthase which is involved in the production of THF from folic acid Also acts as cofactor in molecular rearrangement reactions (e.g. metabolism of branched-chain amino B acids) – particularly in the central nervous system Vitamin B12 De7ciency state DeHciency cause pernicious anaemia – megaloblastic anaemia plus gastrointestinal (diarrhoea, loss of bladder control) and neurological symptoms (seizures, degeneration of spinal cord) Folic acid supplementation can reverse the megaloblastic anaemia but will not reverse the other symptoms Care must be taken with anaemic patients to balance intake of folic acid, cobalamin and iron B End of Part 3