The vitamin B 12 added to the human diet largely comes from ruminant stomach of the cow that provides for Vitamin B 12 . Cobalt can be provided in such large quantities that copper assimilation is affected.
Cobalt is only available to a few bacteria and algae.
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.