Vitamin B12 is a water-soluble vitamin. Water-soluble vitamins dissolve in water. After the body uses these vitamins, leftover amounts leave the body through the urine.

Typically, water-soluble vitamins can not be stored by the body. Vitamin B12 is special, because the body can store it for years in the liver.

Vitamin B12 is important for metabolism. Metabolism within the body includes the processes of energy generation and use; including nutrition, digestion, absorption, elimination, respiration, circulation, and temperature regulation.

The human body stores several years' worth of vitamin B12, so nutritional deficiency of this vitamin is extremely rare. Although, people who follow a strict vegetarian diet and do not consume eggs or dairy products may require vitamin B12 supplements.