When I do a nutrition consult one of the first things that I ask a client is the types of medication or supplements that they are taking. Here is a common dialogue:

"So what sorts of supplements are you taking on a regular basis?"
"Calcium for my bones and vitamin B12 for energy."
"mmmhmm..."

      I think Dr.Bernstein has played a role in the myth of the magical energy producing effects of vitamin B12 due to the fact that he requires his patients to purchase B vitamin cocktail injections.
      The reality is that unless you are actually vitamin 12 deficient, which can cause some lethargy, supplementing will not affect your energy levels. Even deficient individuals may not notice an energy difference after supplementation. Vitamin B12 deficiency may occur in those who have absorption problems (such as Crohns, colitis, or celiac disease) or vegans as B12 is found in meat and dairy products.
      The B vitamins help to turn carbohydrate energy into fuel,and can be called a cofactor in metabolism, but they do not give you energy or improve your metabolic rate
 
   Check out this website for more information on the vitamin B12 energy myth.http://www.quickanddirtytips.com/health-fitness/healthy-eating/do-b-vitamins-give-you-energy