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Because vitamin B12 is a water soluble vitamin, excess amounts are eliminated through urination. Studies show that even in large doses, vitamin B12 is not toxic.
Vitamin B12 can be found in foods as well as supplement form. Foods containing B12 include meats, dairy products and eggs.
Lots of information about vitamin B12 can be found here - http://www.vitamins-supplements.org/vitamin-B12-cyanocobalamin.php
While the average daily requirement of B12 is only 2 mcg, much more can safely be ingested, and any excess will be excreted by the body.
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