Vitamin B12 is a water soluble vitamin that is naturally found in diary product, meats and fish.  Synthetic vitamin b12 is also found in fortified foods, like cereals and breads.  Vitamin B12 is critical for your health.  It is needed for red blood cells to form properly, DNA synthesis and proper neurological function.

The absorption of vitamin b12 is a fairly complex biological process.  When b12 is consumed in its natural form, it is bound to the protein in food.  B12 is separated from the protein through the work of gastric protease and hydrochloric acid in the stomach.  The B12 then combines with a substance called intrinsic factor to complete the absorption process.  Intrinsic factor is a glycoprotein that is created in the stomach.

The key issue that most people have with is not that they do not consume enough b12, but rather that their body had a difficult time absorbing b12.  Even if an individual consumes enough b12, pernicious anemia is an autoimmune disease that can lead to a serious b12 deficiency.  Pernicious anemia causes gastric atrophy which causes the body to stop producing intrinsic factor.  It can also cause the destruction of parietal cells.  Untreated, pernicious anemia will cause serious neurological issues that are often irreversible.

Even in the absence of pernicious anemia, many people have difficulty in absorbing vitamin b12.  As an example, heavy drinkers often have low levels of b12 because their folate levels are not sufficient for b12 absorption.  Because intrinsic factor production decreases with age, older individuals are also at risk of having low levels of b12.

Oral supplementation does not help if your body is already low on its supply of vitamin b12.  The average b12 supplement has 100 mcg of b12.  Although 56% of a 1mcg supplement is absorbed, little beyond this is ever absorbed.  This is because there is not enough intrinsic factor in the body to absorb above this amount.

For this reason, many people who are at risk of developing a b12 deficiency decide to take a vitamin b12 injection. A b-12 shot is the best solution for those that have absorption issues because the b12 is fed directly into the blood stream.