Getting too much vitamin B12 has no known symptoms or toxicity. Since it is water-soluble, any extra leaves the body in the urine. There is no proof that taking extra B12 boosts energy. Vitamins do not create energy. They do not provide calories to the body for energy.
Vitamins help breakdown nutrients that are energy-yielding.
These nutrients include carbohydrate, protein, and fat. Calcium is necessary for normal absorption of vitamin B12. A deficiency of either iron or vitamin B6 can decrease the absorption of B12.