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Vitamin B12

WATER-SOLUBLE

Methylcobalamin, Adenosylcobalamin

Vitamin B12 (cobalamin) is the largest and most chemically complex of all vitamins, containing a cobalt atom at the center of a corrin ring structure. It is synthesized exclusively by bacteria and enters the human food chain through animal products. B12 is unique among vitamins in that its absorption requires intrinsic factor — a glycoprotein secreted by stomach parietal cells. The body stores approximately 2-5 mg in the liver, which can sustain normal function for 2-5 years.

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Key Functions

  • DNA synthesis
  • Red blood cell formation
  • Neurological function and myelin maintenance
  • Methylation reactions
  • Fatty acid metabolism

Best Food Sources

Meat, poultry, and fishEggs and dairy productsClams and organ meatsFortified cereals and plant milksNutritional yeast

Deficiency: Vitamin B12 Deficiency

  • Megaloblastic anemia
  • Fatigue and weakness
  • Numbness and tingling in extremities
  • Difficulty walking and balance problems
  • Memory loss and cognitive changes

High-Risk Groups

  • Vegans and strict vegetarians
  • Adults over 50
  • People with pernicious anemia
  • Those who've had gastric bypass surgery
  • People taking metformin or PPIs

Reviewed for accuracy: Content is based on guidelines from the NIH Office of Dietary Supplements, Harvard T.H. Chan School of Public Health, and peer-reviewed medical literature.

Recommended Daily Amount

Adult Men

2.4 mcg

Adult Women

2.4 mcg

Did You Know?

B12 is found almost exclusively in animal products. Vegans must supplement to avoid deficiency, which can take 2-5 years to develop.

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