Vitamins

• Water soluble vitamins


  Readily soluble in water and absorbed without the involvement of fat. Excess intakes are excreted in the urine.
• Water soluble vitamins


  • Some are stored for a short period while 2 or 3 are stored in the body for up to 2 months
  • They function as co-enzymes and all except Vitamin C and Biotin must be metabolically converted to their active forms
• Thiamine (Vitamin B1)


  Reacts with ATP to form Thiamine pyrophosphate (TPP), the active form of the vitamin in biochemical reactions
• Thiamine activation

  Rapidly converted to its active form, thiamine pyrophosphate, TPP, by the enzyme thiamine pyrophosphokinase 1, (TPK1)
• TPP

  • Necessary as a cofactor for three very important dehydrogenases: pyruvate dehydrogenase complex (PDHc), α-ketoglutarate dehydrogenase (OGDH), and branched-chain ketoacid dehydrogenase (BCKD)
  • Also a coenzyme in transketolase and transaldolase reactions

  
• Thiamine deficiency


  Associated with elevated levels of pyruvate and lactate
• Sources of Thiamine


  • Unpolished rice
  • Whole grains such as maize
  • Nuts
  • Potatoes
  • Brewer's yeast
• Thiamine is easily destroyed by heat, so the thiamine content of foods is lowered by cooking
• Thiamine requirement


  Linked to caloric intake
• Causes of Thiamine deficiency

  • Anorexia
  • Diarrhea
  • Alcoholics
  • Post-operative patients
• Types of Beriberi


  • Central nervous system affected
  • Heart affected leading to Cardiac failure and edema
  • GIT affected causing indigestion and anorexia
• Prolonged dietary deficiency in thiamine leads to wet beri beri
• Central nervous system disorder manifestations are the major features of dry Beriberi, peripheral neuritis with sensory nerves disturbances leading to complete paralysis
• Wernicke's encephalopathy is seen in Alcoholics with TPP deficiency
• Riboflavin (Vitamin B2)

  The electron carrier co-enzymes that exist as FAD and FMN
• Functions of Riboflavin

  • Involved in a variety of redox reactions catalysed by oxidases, reductases and dehydrogenases (fatty acid synthesis, TCA cycle and amino acid synthesis)
  • Necessary for aerobic respiration and tissue maintenance
• Riboflavin deficiency is widespread but not fatal
• Symptoms of Riboflavin deficiency

  • Angular stomatis
  • Cheilosis
  • Desquamation
  • Inflammation of the tongue
• Riboflavin deficiency can also be observed in newborns treated for hyperbilirubinemia by phototherapy
• Sources of Riboflavin

  • Liver
  • Kidney
  • Green leafy vegetables
  • Milk and dairy products
• Niacin (Vitamin B3)

  The precursors of the co-enzymes NAD+ and NADP+
• Functions of Niacin

  • Essential coenzymes in numerous cellular redox reactions, lipid biosynthesis, the pentose phosphate pathway and amino acid metabolism
• Niacin deficiency

  Causes the disease pellagra
• Symptoms of Niacin deficiency

  • Photosensitive dermatitis on skin
  • Impaired digestion
  • Diarrhea
  • Mental confusion
• Sufficient quantity of Niacin can be synthesized endogenously from tryptophan
• Sources of Niacin

  • Meats
  • Fish
  • Nuts
• Pantothenic acid (Vitamin B5)

  Precursor of co-enzyme A, that participates in acyl transfer reactions
• Functions of Pantothenic acid

  • Coenzyme A is the carrier for acetyl groups obtained from the degradation of carbohydrates and lipids
  • Coenzyme A also carries the acetyl and malonyl groups used in fatty acid synthesis
• Vitamin B5 deficiency has not been observed in humans
• Sources of Pantothenic acid

  • Beef liver
  • Peanuts
  • Soybeans
  • Wheat germ
• Pyridoxine (Vitamin B6)

  The biologically active forms are pyridoxamine phosphate and pyridoxal phosphate, mostly involved in amino acid metabolism
• Functions of Pyridoxine

  • Involved in various transaminations and oxidation reactions
  • Involved in the synthesis of various transmitters such as serotonin, dopamine and epinephrine
• Symptoms of Pyridoxine deficiency

  • Irritability
  • Mental confusion
  • Convulsions (in infants)
  • Peripheral neuropathy
  • Inflammation of the mouth
• The daily requirement of Pyridoxine varies with the daily protein intake
• Biotin (Vitamin H)

  The coenzyme for cellular carboxylation reactions
• Biotin is synthesized by the intestinal flora in amounts believed sufficient to meet the daily needs of humans
• Biotin deficiency has not been observed in humans on a normal diet
• Raw egg contains a protein called avidin that binds biotin very tightly and prevents its absorption
• Sources of Biotin


  • Liver
  • Peanuts
• Folic acid (Vitamin B9)


  Converted to tetrahydrofolate, the primary carrier of one carbon units in the cells