Vitamin B12 (Cobalamin)
Requirements:
Daily Optimal Intake:
Supplement Forms:
- Cyanocobalamin - orally, but oral, sublingual, or intranasal
administration of B12 is only rarely effective
- Hydroxycobalamin - injectable - is longer acting and achieves
higher B12 levels than cyanocobalamin
Labs:
- 24 hour urine MMA - very sensitive and very expensive
- Schilling test - used to assess deficiency cause
- Serum B12 (microbial assay)
Food Sources:
- Beef 3 oz. (2.1 mcg.)
- Beef liver 3 oz. (94 mcg.)
- Brewer's yeast 2 Tbl. (2.0 mcg.)
- Cheese 3 oz. (0.9 mcg.)
- Chicken 3 oz. (0.3 mcg.)
- Clams 3 oz. (59 mcg.)
- Egg 1 large (0.6 mcg.)
- Halibut 3 oz. (0.8 mcg.)
- Lamb 3 oz. (2.6 mcg.)
- Lobster 3 oz. (2.5 mcg.)
- Milk 8 oz. (0.9 mcg.)
- Salmon steak 3 oz. (3.0 mcg.)
- Tuna, canned 3 oz. (1.3 mcg.)
Signs and Symptoms of Deficiency:
- Achlorhydria
- Classic pernicious anemia due to a lack of IF (intrinsic
factor)
- Confusion
- Decreased phagocyte and PMN response
- Depression
- Fatigue
- Glossitis
- Impaired lymphocyte response
- Memory loss
- Progressive peripheral neuropathy with pronounced anemia
- Psychosis
- Spinal degeneration and macrocytic cells
Causes of Deficiency:
- Achlorhydria
- Deficiency of intrinsic factor
- Gastrectomy
- Liver disease or cancer
- Malabsorption, i.e., celiac disease, colitis, etc.
- Megadoses of vitamin C and/or copper
- Pregnancy
- Tapeworms
- Vegans
Adverse Effects and Toxicity:
Drug/Nutrient Interactions:
- Excessive anticonvulsants may cause deficiency
of B12
- Excessive antibiotics may cause deficiency
of B12
- Large doses of vitamin B12 may increase the requirement for
folate
- Megadoses of vitamin C and/or copper may cause deficiency of
B12
- Nitrous oxide treatment interferes with vitamin B12 metabolism which may lead to megaloblastic anemia
- Cholestyramine decreases vitamin B12 absorption
- Due to ingibition of gastric acid and pepsin secretion by cimetidine, vitamin B12 is not absorbed
- Clofibrate decreases vitamin B12 absorption
- Colchicine decreases vitamin B12 absorption
- Neomycin decreases vitamin B12 absorption
- Aminopterin decreases vitamin B12 absorption
- Omeprazole causes significant short term vitamn B12 malabsorption
- Para-aminosalicylic acid decreases vitamin B12 absorption
- Phenformin decreases vitamin B12 absorption
- Phenytoin decreases vitamin B12 absorption
- H-2 blockers decreases vitamin B12 absorption
- Potassium chloride decreases vitamin B12 absorption
- Potassium citrate decreases vitamin B12 absorption
- Some oral hypoglycemic agents decrease vitamin B12 absorption
- Rantidine decreases vitamin B12 absorption
- Tetracycline decreases vitamin B12 absorption
- Oral contraceptives decrease vitamin B12 absorption
Biochemical Functions:
- B12 assists in transferring the methyl group onto homocysteine
to form methionine, which is necessary for the synthesis of myelin
sheaths
- Cofactor in the transfer of methyl groups - takes the methyl
group from methyl tetrahydrofolate so that THF, the active form of
folate, can be used for synthesis of DNA
- Involved in carbohydrate metabolism
Clinical Indications:
Copyright 1998 - 2008 by L. Vicky Crouse, ND and James S. Reiley, ND. All rights reserved (ISSN 1527-0661).