A unique feature of vitamin B12 is that unlike other vitamins, animal sources are the only reliable sources for its intake. Vitamin B12 is primarily found in meat, eggs, dairy products and fish.

A valuable source of vitamin B12 is calves liver (one pound per day), which contains such a high quantity of vitamin B12 that even people who lack the intrinsic factor can absorb this in sufficient amounts to prevent pernicious anemia (a disease caused by deficiency of this vitamin).

There is much controversy vis--vis the proposed plant sources of vitamin B12. Some findings suggest that fermented soya products, seaweeds (named nori), and algae such as spirulina all contain significant amounts of vitamin B12. However, analysis reveals that due to the presence of compounds structurally similar to vitamin B12, termed as B12 analogues, there is difficulty in distinguishing between the two forms and these cannot be utilized to satisfy dietary needs. The most prevalent view today is that plant sources of vitamin B12 are not likely to be available to humans and hence cannot be tagged as safe sources of the vitamin.

There is some question as to whether vegetarians and vegans acquire enough vitamin B12. They are at a risk of developing a deficiency syndrome because natural food sources of this vitamin are limited to animal foods. Hence, vegetarians are advised to include a rich intake of foods fortified with vitamin B12 within their diet schedule. Good sources of this vitamin are fortified cereals, dairy products like soya milk, free-range eggs and sunflower margarines. Strict vegetarians and vegans who do not even consume plant foods fortified with vitamin B12 need to consider taking a in a supplement that contains vitamin B12 either in oral or dietary form.

There are claims that vitamin B12 can be consistently obtained from nutritional yeasts. However, one should be aware that there is no substantial proof to validate such a claim.

Bacteria exclusively synthesize vitamin B12. Streptomyces griseus, a bacterium once thought to be a yeast, was once a source of vitamin B12. Now, the bacteria Propionibacterium shermanii and Pseudomonas denitrificans have replaced it as the latest commercial sources.

Some foods, along with their vitamin B12 content in micrograms (mcg), include

Crab (steamed), 3 ounces8.8 mcg; Salmon (baked), 3 ounces2.4 mcg; Rockfish (baked), 3 ounces1.0 mcg; Beef (cooked), 3 ounces2.1mcg; Chicken (roasted), 3 ounces0.3 mcg; Turkey (roasted), 3ounces0.3 mcg; Egg (poached), 1 large0.4 mcg; Milk, 8 ounces0.9 mcg; Brie (cheese), 1 ounce 0.5 mcg.