Without B12 the brain and nervous system cannot function properly, cells cannot produce adequate energy or synthesize DNA. We also need B12 to make red blood cells. Without adequate numbers of properly functioning red blood cells oxygen cannot be supplied to all the cells in the body that need it and we have a condition known as anemia, which basically means oxygen deficiency. The type of anemia associated with B12 deficiency is known as “pernicious anemia” and occurs when the vitamin cannot be absorbed from the digestive tract into the bloodstream in adequate amounts.
The absorption of vitamin B12 is a complex process. In food, the vitamin is bound to proteins which have to be broken down before it can be absorbed. And this can only happen when there's adequate acid production in the stomach, which as we get older, tends to be a problem since acid levels decrease with age. But release of vitamin B12 from its protein coat is only the first step in the absorption of the vitamin. Absorption actually takes place in the small intestine and requires the presence of a special protein produced by the cells in the stomach called “intrinsic factor”. The only way absorption can occur in the blood stream is when the right amounts of both B12 and intrinsic factor are present. Without them, deficiency can occur. This can be due to a number of reasons, such as a lack of B12 in the diet, reduced stomach acidity, or when particular cells in the stomach - the "parietal" cells - do not produce enough intrinsic factor. Referred to as "pernicious anemia", this happens when, for some unknown reason, the immune system attacks and destroys the parietal cells thereby causing an inability to absorb B12.
Signs of vitamin B12 deficiency can take quite some time to appear and, upon doing so, appear in a subtle fashion. For example, B12 is needed for the maintenance of myelin, the protective coating around nerve cells. If this wears away, tingling sensations, numbness and a burning feeling in limbs can occur along with memory problems and mood disorders. These types of symptoms do not immediately trigger one to associate with that of a vitamin deficiency. On the other hand, the impairment of red blood cells’ ability to carry oxygen is a more dramatic effect of a B12 deficiency. In the absence of B12, these cells grow to an abnormally large size as they try to capture more oxygen. The technical term used to describe this condition is "macrocytic anemia".
Monthly B12 injections or high dose oral supplements (0.5 mg) can be prescribed to correct a diagnosed deficiency but many researchers feel that it is a good idea for everyone over the age of 50 to take a B12 supplement, which includes at least the daily value of 2.4 micrograms. Some experts may even recommend higher doses, of up to 25 micrograms. Cyanocobalamin is the common B12 supplement, and while it is not present in nature when in the liver it can be converted to methylcobalamine or adenosylcobalamin, the physiologically active forms of the vitamin. Several years worth of vitamin B12 can be stored in the liver so it may take a significant amount of time for a deficiency to occur. The cyanocobalamine used in supplements is produced when the resulting product of a bacterial fermentation process passes through activated charcoal. It is during this process that it is converted to cyanocobalamine, which is highly stable and suitable for supplements. There is no risk of overdosing.
Actually, the term “vitamin B12” can refer to any of a class of chemically-related compounds that can be converted to the active form in the body. In nature, only bacteria can make these compounds. But since they can inhabit the guts of animals, us humans can get our B12 intake from meat. Animals themselves are often supplemented with B12 in their feed. In fact, most of the world’s production of this vitamin is destined for use as a feed additive to ensure the health of farm animals. Vegans, as they are not meat-eaters, have to rely on supplements for their B12 intake.
But it is not only the elderly who have to worry about vitamin B12 deficiency. A study coming out of Tufts University showed that 40% of young adults studied had low levels of the vitamin, despite their "healthy" diets. It seems that B12 from meat, chicken and fish is not as well absorbed as we thought; absorption from dairy products is much better. A glass of milk, for example, can yield a microgram of B12. It is also possible that cooking helps to bind the vitamin more strongly to proteins. Some cereals, such as Protein 19, are fortified significantly, but others such as Corn Flakes are not. So regardless of age, it is a good idea for everyone to make sure they take a daily supplement of vitamin B12 and be sure to consume enough dairy products.
And do it while you can still remember to do so. B12 deficiency impairs memory.