Vitamin B12 & folate

• Vitamin B12


  Also known as cobalamin, an essential nutrient required for various bodily functions
• Folate


  Also known as vitamin B9, an essential nutrient required for various bodily functions
• Vitamin B12 and Folate Metabolism
• Lecture outline includes: Chemistry, Functions & Role, Sources, absorption, Storage, Consequences of Lack, Laboratory Studies
• Lecture Objectives: 1. Explain the metabolism & role of vit.B12,and folate 2.Outline the laboratory studies
• Vitamin B12 - Isolated in 1948

  Active compounds: Cyanocobalamin, Hydroxocobalamim, Nitrocobalamin
• Vitamin B12 - 2 biochemically active coenzymes


  Methylcobalamin, 5"deoxyadenosylcobalamin
• Vitamin B12 Role & Function

  1. Transfer of methyl groups

  2. Intramolecular exchanges of H

  3. Synthesis of methionine from homocysteine

  4. Synthesis of SuccinylCoA from MethylmalonylCoA

  5. Conversion of RNA to DNA
• Vitamin B12


  • Regulates the formation of red blood cells by helping iron function better in the body
  • S-adenosylmethionine is involved in immune function and mood regulation
• Vitamin B12 Daily Requirements

  • 2mg per day-WHO
  • 0.3- 2ug mg per day –children
  • 3.0ug-pregnant women
• Folate


  Also known as Vit B9 Complex, folate, folinic acid, vitamin M, one of the water soluble B vitamins
• Folate Role and Function

  1. Transfer of one C fragments between molecule in red cell

  2. Deoxyuridygylate -> thymindylate (rate limiting step in DNA synthesis and requires N5 N10 methylene FH4)

  3. Steps in Purine synthesis
• Vitamin B12 Rich Sources

  • Fish, dairy products, organ meats (particularly liver and kidney), eggs, beef, and pork
• Folate Rich Sources


  • Leafy vegetables such as spinach, lettuces, beans and peas, fruits and vegetables
• Vitamin B12 Absorption


  Cobalamin + carrier protein - pancreatic proteases in the proximal small intestine - transferred to the IF then absorbed together in the ileum
• Folate Absorption


  1. Folate attached to multiple glutamic acid molecules which must be removed by hydrolysis prior to absorption by Vit B12 dependent enzyme

  2. Absorption is by passive diffusion at the deudenum and jejunum
• Vitamin B12 Serum Levels

  160 – 925 ng/l
• Folate Serum Levels


  3 – 6 µg /ml
• Vitamin B12 Half Life

  Approximately 6 days (400 days in the liver)
• Folate Half Life


  3 - 4 months
• Vitamin B12 Cooking Effect

  20 – 50% loss
• Folate Cooking Effect


  50 - 90% loss
• Vitamin B12 Functions


  1. Coenzyme in nucleic acid synthesis

  2. Maintain integrity of CNS

  3. Required in folate metabolism
• Folate Functions


  1. Catalysts in nucleic synthesis

  2. Folate co-enzymes are required for transfer of one carbon units from one compound to another
• Vitamin B12 Deficiency Seen In

  • Surgery
  • D.latum,
  • Pernicious anemia
  • Vegetarians
  • Smokers
  • Alcoholics
• Folate Deficiency Seen In

  • Pregnancy
  • Lactation
  • Alcoholics
  • Smokers
  • Elderly
  • Chronic haemolytic disorders
• Vitamin B12 Lab Studies

  • TBC
  • PBF (Macroovalocytes,hypersegmented neutrophils)
  • Reticulocyte count
  • Vit B12 levels
  • Folate Levels
  • IF Assays