B12 comes from animal sources.
Strict vegetarians who wash their food well will need supplementation of B12 to survive.
B12 is absorbed in a complicated fashion. Any problem along the chain that leads to absorption and storage in the liver will result in it being passed through the body in fecal material.
B12 is first freed from its protein bonds by acid in the stomach. As a result, anything that depletes or lowers stomach acid (such as proton pump inhibitors and antacids) will damage the body's ability to take in B12 because bound B12 cannot progress to the next step in the chain of events. It will be passed through the body in fecal material.
Intrinsic Factor is secreted in the stomach. This special chemical's job is to bind to the newly freed B12 and carry it through the wall of the small intestine and into the blood stream. If there is insufficient intrinsic factor, B12 will not be able to progress to the next step in the chain of events. It will be passed through the body in fecal material.
Once carried into the bloodstream, B12 is carried to the liver where it is stored until it is needed. The liver can store 3-5 years worth of B12 before it runs out completely. If B12 is not carried into the bloodstream in the small intestine, it will be passed through the body in fecal material.
Because B12 is involved in many, many vitally important chemical reactions within the body, it can be lifesaving to diagnose a problem and treat it asap.
Patients who have trouble absorbing B12 are:
- The elderly.
- Anyone taking long term preparations to lower stomach acidity.
- Those who have had stomach reduction surgery.
- Those with pernicious anemia - an autoimmune condition in which the immune system attacks the cells that make intrinsic factor.
- Those with Sjogren's Syndrome and accompanying problems with the glands that either secrete stomach acid or intrinsic factor.
- Those with digestive problems which include the small intestine.
Some patients have luck using oral B12 supplements at extremely high doses, however because of the danger of permanent damage, injection therapy is usually started to be sure the patient receives enough B12. Sublingual preparations are often effective and are relatively inexpensive. There is currently a B12 nose spray that is also quite effective, but also prohibitively expensive and not covered by insurance, so not often utilized.
B12 injections used to be given only in the muscle (IM) however, giving injections subcutaneously can be just as effective and much easier to accomplish. There is some danger of tissue problems with subQ injections, but many find the slower absorption of SubQ injections to be easier on their systems.
B12 injections are usually begun promptly upon diagnosis.