Coordination Compound : Vitamin B12: Sources of Vitamin B12

• Foods

Vitamin B12 is naturally found in meat (especially liver and shellfish), milk and eggs. Animals, in turn, must obtain it directly or indirectly from bacteria, and these bacteria may inhabit a section of the gut which is posterior to the section where B12 is absorbed. Thus, herbivorous animals must either obtain B12 from bacteria in their rumens. Eggs are often mentioned as a good B12 source, but they also contain a factor that blocks absorption. Certain insects such as termites contain B12 produced by their gut bacteria, in a manner analogous to ruminant animals. While vegetarians usually get enough B12 through consuming dairy products, vitamin B12 may be found to be lacking in those practicing vegan diets who do not use multivitamin supplements or eat B12 fortified foods. Examples of fortified foods often consumed include fortified breakfast cereals, fortified soy-based products, and fortified energy bars. People on a vegan raw food diet are also susceptible to B12 deficiency if no supplementation is used.

Food Sources of Vitamin B12

Excellent Vitamin B12 Food Sources

• Supplements

Vitamin B12 is provided as a supplement in many processed foods, and is also available in vitamin pill form, including multi-vitamins. Vitamin B12 can be supplemented in healthy subjects also by liquid, strip, nasal spray, or injection and is available singly or in combination with other supplements. Cyanocobalamin is converted to its active forms, first hydroxocobalamin and then methylcobalamin and adenosylcobalamin in the liver. The sublingual route, in which B12 is presumably or supposedly absorbed more directly under the tongue, has not proven to be necessary or helpful. Injection is sometimes used in cases where digestive absorption is impaired, but there is some evidence that this course of action may not be necessary with modern high potency oral supplements (such as 500 to 1000 µg or more). Even pernicious anemia can be treated entirely by the oral route.These supplements carry such large doses of the vitamin that the many different components of the B12 absorption system are not required, and enough of the vitamin (only a few µg a day) is obtained simply by mass-action transport across the gut.