Vitamin B-12 is also referred to as cobalamin because cobalt is in the chemical structure. The vitamin has the largest chemical makeup of all the vitamins. The recommended dietary allowance for B-12 is 2.4 micrograms per day. Most Americans easily meet or exceed this RDA without any ill effect. In the diet, vitamin B-12 mostly comes from meat, poultry, fish and shellfish.
No Upper Limit
There is no known toxicity for vitamin B-12. The body absorbs only a small amount of vitamin B-12, which is why there is no toxicity. Because there are no side effects from large doses of vitamin B-12, no tolerable upper intake was ever established.