What foods are a good source of vitamin B-12?

Shellfish, particularly clams and oysters, are among the richest sources of vitamin B-12. Lean beef, chicken, eggs and dairy products also contain large amounts of this necessary nutrient. While most natural B-12 only occurs in animal products, those who avoid animal-based foods can get B-12 from fortified cereals, beverages and grains.

B-12's chemical name is cobalamin, and unlike many other vitamins, which are typically available from a number of different sources, it is only naturally produced by bacteria. The overwhelming majority of B-12-producing bacteria live in the intestines of other animals, which makes most B-12 only available from animal products.

While most natural B-12 comes from animal products, growing B-12-producing bacteria is also possible. Companies produce B-12 in this way by culturing large amounts of B-12-producing bacteria on pureed sugar beets. After growing the bacteria for some time, they then separate the B-12 from the mush and purify it. For the most part, this is the type of B-12 found in fortified foods and nutritional supplements. While it is still B-12, most people do not absorb this variant of the vitamin as easily as natural B-12.

Scientists can also fully synthesize B-12 from precursor chemicals in laboratories. This allows scientists to faithfully replicate natural B-12 without using animal products, but it also significantly increases costs.