Our primary food sources of vitamin B12 include meat, most fish, especially the oily ones (trout, herring, and mackerel), crabs and oysters, eggs (the yolk), and milk products, especially yogurt. Organ meats such as liver, heart, and kidney are particularly high. The vegan--that is, the strict vegetarian who consumes no animal-source foods--is not getting the necessary vitamin B12 from diet (although tempeh, a fermented soybean product, and some sprouts may contain some vitamin B12); thus, vegans will often need an additional supplement (which absorbs well) or periodic injections.
Functions: Although vitamin B12, cobalamin, apparently does not have as many functions
as some of the other B vitamins, it has some very important ones. It is essential for the metabolism of the nerve tissue and necessary for the health of the entire nervous system. It stimulates growth and increases appetite in children. Cobalamin, along with iron, folic acid, copper, protein, and vitamins C and B6, is needed for the formation of normal red blood cells.
Vitamin B12 is the "energy" vitamin, as it often increases the energy level, whether obtained from eating the B12 foods or from supplemental use. There may be several reasons for this. Cobalamin stimulates the utilization of proteins, fats, and carbohydrates. It also helps iron function better in humans and is important for the synthesis of DNA and RNA, as well as for production of choline, another B vitamin, and methionine, an amino acid.
Uses: Vitamin B12 is generally known as the longevity vitamin, possibly because it helps
the energy level and activity of the nervous system of the elderly. B12 injections (the main therapeutic use of this vitamin) have been a common practice of many doctors for the treatment of fatigue, and, in my experience, it works very often. However, it would only be a "cure" when the tiredness is a result of B12 deficiency. There are many reasons for fatigue. As we age, our digestion and absorption are not usually as finely tuned as when we were young, particularly when we eat and live the way most of us late twentieth-century beings do. And vitamin B12, even though it is needed in such small doses, is one of the most difficult vitamins to acquire through diet and to metabolize. The "red vitamin" is the main "antifatigue" vitamin; often given along with folic acid, it helps energy and prevents most anemia, provided there is good iron absorption and hydrochloric acid production.
Medically speaking, it is wise to check patients with fatigue for anemia and to measure vitamin B12 and folic acid levels before embarking on a treatment regimen.
B12, given intramuscularly, usually in doses of 500-1,000 mcg. (0.5-1.0 mg.), is used once, twice, or three times weekly for a period of time to both give energy and, in adults, help with appetite suppression in weight loss programs. These amounts also replenish the vitamin B12 stores. It has a mild diuretic effect as well and may be used premenstrually to diminish water retention symptoms.
In the treatment of pernicious anemia and the earlier symptoms of vitamin B12 deficiency, injections of cobalamin or its variants are usually necessary because most everyone with deficiency has poor absorption. It is difficult to become B12 deficient from diet alone, unless we are on a strict vegan diet for years. In any anemia, really, it is wise to supplement B12, because it helps the red blood cells develop to a point where protein, folic acid, iron, and vitamin C can then complete their maturation so that we can better carry oxygen and energy to all of our cells.