Recommended daily allowance
Cobalt are assimilated only by intake of vitamin B12, and not in its ionic or metallic form. Therefore, there is no clear recommended amounts of cobalt because there are just recommendations for vitamin B12. In this vitamin it is absorbed in the amount of 5-8 micrograms per day.
If the cobalt enters the body in some other form, then it can be very toxic. Lethal doses of cobalt (LD50) are about 150-500 miligrams per kilogram of body weight.