Vitamin B12 works with folic acid and vitamin
B6 to decrease blood levels of homocysteine, which is associated
with an increased risk of coronary heart disease. It is also used for
the treatment of pernicious anemia.
Sources
Beef, liver, clams, lamb - all contain 80 to 100 mcg of B12 per 3.5
ounce serving. Sardines, chicken liver, beef kidney, calf liver - all
contain 25 to 60 mcg per serving. Trout, salmon, tuna, eggs, whey and
many cheeses contain at least the RDA (>2 mcg) per serving. It is
also found in sea vegetables such as dulse, kelp, kombu and nori, as
well as soy products. Vegetarians may need to take supplemental forms
of vitamin B12 because most sources are from animal products.
Therapeutic dosage
In the absence of pernicious anemia, the RDA of 2 mcg per day is
sufficient, best in the form of B-complex supplement (if not a food source).
Safety concerns
Extremely safe in recommended doses.
Interactions
You may need more vitamin B12 if you are also taking long-term sulfa
antibiotics, stomach acid reducing medications, phenobarbital,
colchicine, corticosteroids, antipsychotic medications, isoniazid,
methotrexate, methyldopa, phenformin, oral contraceptives,
triamterene (Maxide), cholestyramine, colestipol, or clofibrate. If
you are taking higher than the RDA for potassium, you may need extra
vitamin B12. High doses of vitamin C supplementation may interfere
with blood tests for vitamin B12 deficiency.