The most important function of 12 b is to form healthy red blood cells. However, all cells need 12 b to keep them healthy. It is the white blood cells, amongst others, that need 12 b to help ensure that the immune system functioning properly.
All of the nerve cells in the body also need 12 b to form their protective fatty layer. This is essential for all of the nerves but is especially so for those in the brain. If there is not sufficient 12 b to create this protective layer then the brain will not be functioning properly.
To help the body absorb 12 b the stomach produces intrinsic factor which enables more of the 12 b to be absorbed. 12 b is only found in animal foods such as liver, eggs, fish and meat but most people consume far more than their recommended daily amount of 12 b.
This is not a problem as the body can only absorb about half of the 12 b that is consumed. It is also worth noting that the body can recycle the 12 b which cuts down on the impact of a 12 b deficiency. However, strict vegetarians or vegans are likely to require 12 b supplements if they do not eat any animal products that contain 12 b.