Ways to Get B12 Deficiency

(Reference: Herbert (1) where not otherwise noted.)

  • Inadequate dietary intake.
  • Inadequate absorption:
    • Pernicious anemia - Problems with intrinsic factor.
      • Loss of intrinsic factor: Genetically predetermined and age-dependent (sometimes as early as 45 yrs). The most common cause of B12 deficiency in non-edlerly, nonvegetarians.
      • Autoimmunity to intrinsic factor: Circulating antibodies to intrinsic factor indicate eventual pernicious anemia if not treated. A chronic B12 deficiency damages immune function and the antibodies may disappear as B12 deficiency progresses.
    • Food-cobalamin malabsorption - Loss of gastric acid and/or protein digesting enzymes which break the protein-B12 bonds in food. This can be caused by stomach surgery, atrophy or inflammation of the stomach, medications that suppress acid secretion, or a stomach infection by H. pylori or anaerobic bacteria (which can be due to low stomach acid) (2).
    • Pancreatic disease reduces free calcium in the ileum (calcium is needed for B12 absorption). Can be improved with calcium and/or bicarbonate.
    • Unhealthy ileum.
    • Drugs decreasing absorption include cimetidine, metformin (ties up free calcium in intestines), potassium chloride, and cholestyramine (3).
    • Infection by tapeworms (4),Diphyllobothrium latum (5), or Giardia lamblia (3).
  • Defects in B12 enzymes, transport proteins, or storage proteins.
    • Defects in B12 enzymes that result in high MMA levels are rare. One researcher reported that they occur in 1 out of 28,000 people (6). Ciani et al (6). provide an informative diagram showing which enzymes are involved in the various B12 metabolic pathway defects.
  • Increased requirement during pregnancy or hyperthyroidism.
  • Increased excretion caused by alcoholism.
  • Nitrous oxide anesthesia in people with low serum B12 (nitrous oxide can change the cobalt atom of B12) (4).
  • Hypothyroidism (possibly autoimmune) (7).
  • AIDS can cause B12 deficiency as shown through macrocytic anemia and neurological problems without elevated homocysteine levels.


1. Herbert V. Staging vitamin B-12 (cobalamin) status in vegetarians. Am J Clin Nutr. 1994 May;59(5 Suppl):1213S-1222S.

2. Ho C, Kauwell GP, Bailey LB. Practitioners' guide to meeting the vitamin B-12 recommended dietary allowance for people aged 51 years and older. J Am Diet Assoc. 1999 Jun;99(6):725-7.

3. Tucker KL, Rich S, Rosenberg I, Jacques P, Dallal G, Wilson PW, Selhub J. Plasma vitamin B-12 concentrations relate to intake source in the Framingham Offspring study. Am J Clin Nutr. 2000 Feb;71(2):514-22.

4. Groff J, Gropper S. Advanced Nutrition and Human Metabolism, 3rd ed. Wadsworth: 2000.

5. Halsted JA, Carroll J, Rubert S. Serum and tissue concentration of vitamin B12 in certain pathologic states. N Engl J Med. 1959;260:575-80.

6. Ciani F, Poggi GM, Pasquini E, Donati MA, Zammarchi E. Prolonged exclusive breast-feeding from vegan mother causing an acute onset of isolated methylmalonic aciduria due to a mild mutase deficiency. Clin Nutr. 2000 Apr;19(2):137-9.

7. Johnson PR Jr, Roloff JS. Vitamin B12 deficiency in an infant strictly breast-fed by a mother with latent pernicious anemia. J Pediatr. 1982 Jun;100(6):917-9.