The need for Vitamin B 12 requires a diet include a few diet products from a ruminant animal, either in the form of dairy products or meats. There is no known cobalt deficiency in plants, but it is necessary for nitrogen fixing bacteria in legumes. It is also required for a few bacteria and algae. It is also required for the bacteria used in digestion of ruminant animals such as cattle, sheep and deer. In solution it can be toxic in quantities greater than 0.1 ppm.
Effective absorption requires intervention of carriers, able to bind the vitamin.
There is no convincing evidence that cobalt is needed in the human diet when Vitamin B 12 is available. An average daily need for Vitamin B 12 range from 0.3 to 2.6 micrograms a day. Humans obtain Vitamin B 12 from meat and diary products, and plants do not make Vitamin B 12 . Yeast is high in Vitamin B 12 . A deficiency in cobalt may be responsible for slow growth rate and permanent nervous disorders can result from deficiency.