Vitamin B12 is an essential water-soluble B-complex vitamin vital to healthy red blood and nerve cell maintenance, DNA production and metabolic function. While the body excretes excesses of other water-soluble vitamins, it has the capacity to store several years worth of vitamin B12 in the liver, making deficiencies unusual. Vitamin B12 deficiencies are most often seen in the elderly, who have a diminished capacity to absorb it; in individuals with genetic malabsorption disorders; and in strict vegetarians and vegans who have limited dietary vitamin B12 options. The National Institutes of Health Office of Dietary Supplements recommends healthy adults consume 2.4 mcg of vitamin B12 daily.
Meat, Poultry, Fish and Seafood
Beef liver is one of the richest food sources of vitamin B12, offering approximately 800 percent of the recommended dietary allowance, or RDA, in a one-slice serving. A 3-oz. serving of top sirloin contains 40 percent of the RDA, while a double-patty cheeseburger has approximately 30 percent of the RDA. A 3-oz. serving of clams provides 570 percent of the RDA, while similar portions of trout and salmon offer 90 percent and 80 percent of the RDA, respectively. A medium roast chicken breast contains 12 percent of the RDA.
Dairy and Eggs
While dairy and eggs do not contain as much vitamin B12 as meat, poultry, fish and seafood, they still represent a significant source of this vitamin. Just 1 cup of plain yogurt supplies 25 percent of the RDA, 1 cup of milk has 15 percent and 1 large egg has 10 percent.
Fortified Foods
Naturally occurring vitamin B12 is bound to a protein, and the body must separate the two in order to absorb the vitamin. The supplemental vitamin B12 found in fortified breakfast cereals is not bound to a protein, allowing the body to skip the release step. Fortified breakfast cereals contain anywhere from 25 to 100 percent of the vitamin B12 RDA.
Supplements
Vitamin B12 is readily available in supplemental form. Supplemental vitamin B12 is highly bio-available, and absorption is generally limited only by the body's available store of intrinsic factor, a glycoprotein vitamin B12 must bond with before absorption. Because of limited stores of intrinsic factor, healthy adults generally only absorb 10 mcg of a 500 mcg vitamin B supplement.
Mushrooms
An article published in a 2009 issue of the "Journal of Agriculture and Food Chemistry" reported that farmed white button mushrooms contain significant amounts of bio-available vitamin B12 identical to the type found in animal food products.
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