Every cell in the human body requires B12 for energy metabolism. In fact, the entire cellular energy creation, known as the Citric Acid cycle or Kreb’s cycle, depends on it. Unfortunately, the human body cannot create B12 on its own, requiring it from dietary sources.
Clams, mussels, red meat, and dairy are the best natural sources of B12. Supplementing with B12 is safe as no side effects or upper dietary limit exists. The best supplement forms are methylcobalamin and adenosylcobalamin.