Vitamin B12, also known as Cyanocobalamin  is a polycyclic compound containing 3-valent cobalt. Four reduced pyrrole rings are linked together to form a Gulin macroring (similar to porphyrin), which is the only vitamin containing metal elements. Vitamin B12 is a red crystalline powder, odorless and tasteless, slightly soluble in water and ethanol. It is most stable in weak acid with pH value of 4.5-5.0. It decomposes in strong acid (pH < 2) or alkaline solution, and may be destroyed to a certain extent when heated. Higher animals and plants can't make vitamin B12, which is synthesized by microorganisms in nature. Vitamin B12 is the only kind of vitamin that needs the help of intestinal secretion (endogenous factor) to be absorbed. It is involved in the production of bone marrow red blood cells, preventing pernicious anemia and brain nerve damage.