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VITAMINS: Vitamin B-12 (Cobalamin)


Overview of Vitamins | Vitamin A (and Beta Carotene) | Biotin (Vitamin H) | Vitamin B-1 (Thiamin) | Vitamin B-2 (Riboflavin) | Vitamin B-3 (Niacin or Nicotinic Acid) | Vitamin B-5 (Pantothenic Acid) | Vitamin B-6 (Pyridoxine) | Vitamin B-12 (Cobalamin) | Vitamin C (Ascorbic Acid) | Vitamin D | Vitamin E | Folate (Folic Acid) | Inositol | Choline

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Vitamin B-12 (Cobalamin)

Functions of Vitamin B-12

  • Helps in the formation & regeneration of red blood cells, thus helping prevent anemia.
  • Is necessary for carbohydrate, fat & protein metabolism.
  • Maintains a healthy nervous system.
  • Promotes growth in children; increases energy.
  • Is needed for Calcium absorption.

Deficiency Vitamin B-12

  • Stage I (early deficiency): lower serum holoTC II (<60 pg/mL).
  • Stage II: lower serum vitamin B-12 (<300 pg/mL) and holoTC II (<40 pg/mL).
  • Stage III: serum B-12 <200 and holoTC II <40 pg/mL, neutrophil hypersegmentation, elevated serum and urinary methylmalonic acid and homocysteine.
  • Stage IV (severest deficiency): megaloblastic, macrocytic anemia.

Around Stage III (before anemia), potentially irreversible demyelination of spinal cord, brain, and optic and peripheral nerves produces peripheral neuropathy progressing to subacute combined degeneration. Dementia, poor attention span, and depression may be early symptoms.

Note: The stomach secretes intrinsic factor that binds B-12 and mediates its absorption at in the ileum. The main cause of vitamin B-12 deficiency is inadequate intrinsic factor secretion which occurs in pernicious anemia (an autoimmune disease) and in atrophic gastritis (in the elderly). Vitamin B-12 deficiency rarely occurs from low dietary intake, because the absorbed vitamin is secreted in bile and subsequently reabsorbed, so deficiency symptoms can take 20 years to develop from low intakes, e.g., in strict vegetarians. However, in malabsorption, deficiency occurs in months or a few years because absorption from both the diet and enterohepatic circulation is impaired.

People with an increased risk of Vitamin B12 deficiency

  • Strict vegetarians
  • Heavy drinkers
  • Women on the pill
  • People on sleeping pills.

Recommended Daily Allowance of Vitamin B-12

See Recommended dietary allowances for vitamins.

Food sources of vitamin B-12:

Vitamin B-12 is found only in animal products.

  • Excellent sources (>10 g/100g): organ meats and bivalve mollusks such as clams and oysters.
  • Moderate sources (1-10 g/100g): egg yolks, muscle meats and poultry, fish, fermented cheeses and dry milk.
  • Minimal sources (<1 g/100g): Milk and milk products.

Toxicity of vitamin B-12

No toxic effects have been reported when up to 100 g/day are consumed. Intramuscular injections of 100 g are usually given once/month to individuals who cannot absorb the vitamin through their intestine, because of pernicious anemia or other problems.

References