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Vitamin B12

Also indexed as:B12 Vitamin, Adenosylcobalamin, Cobalamin, Cyanocobalamin, Hydroxocobalamin, Hydroxycyanocobalamin, Methylcobalamin

Where to Find It

Vitamin B12 is found in all foods of animal origin, including dairy, eggs, meat, poultry, and fish. According to one report, small, inconsistent amounts occur in seaweed (including nori and chlorella) and tempeh.²⁰ Many researchers and healthcare professionals believe that people cannot rely on vegetarian sources to provide predictably sufficient quantities of vitamin B12. However, another study found substantial amounts of vitamin B12 in nori (at least 55 mcg per 100 grams of dry weight).²¹

Best Form to Take

Cyanocobalamin, a synthetic form of vitamin B12 commonly found in supplements, is normally present only in trace amounts in the body. It has no known biological activity on its own, and must be converted by the body into active forms of vitamin B12. Supplementing with hydroxocobalamin, another form of vitamin B12, results in more sustained levels of vitamin B12 in the body compared with cyanocobalamin and can be used for conditions such as cyanide poisoning (cyanocobalamin should not be used for cyanide poisoning). Partly for these reasons, hydroxocobalamin is to be preferred as a vitamin B12 supplement over cyanocobalamin. Other acceptable forms of vitamin B12 include methylcobalamin and adenosylcobalamin, although there is no clear evidence that these forms (except in very rare cases) are preferable to hydroxocobalamin.²²

How to Use It

Most people do not require vitamin B12 supplements. However, vegans should supplement with at least 2 to 3 mcg per day.

People with pernicious anemia are often treated with injections of vitamin B12. However, oral administration of 1,000 mcg per day can be used reliably as an alternative to vitamin B12 injections.²³^,24^,25^,26^,27

Absorption of vitamin B12 is reduced with increasing age. Some research suggests that elderly people may benefit from 10 to 25 mcg per day of vitamin B12.²⁸^,29^,30 One study of elderly people with vitamin B12 deficiency suggested that as much as 500 to 1,000 mcg of vitamin B12 per day might be necessary to achieve optimal vitamin B12 status.³¹ Vitamin B12 status was measured in this study using a sensitive laboratory test (the plasma methylmalonic acid concentration).

When vitamin B12 is used for therapeutic purposes other than correcting a deficiency, injections are usually necessary to achieve results.

Sublingual forms of vitamin B12 are available,³² but there is no proof that they offer any advantage to oral supplements.