Vitamin B12 is needed for normal nerve cell activity, red blood cell production, and to make DNA. Vitamin B12 is bound to the protein in food. Hydrochloric acid in the stomach releases B12 from protein during digestion. B12 then combines with a substance called intrinsic factor (IF) before it is absorbed into the bloodstream.
Those who eat a normal diet should be able to receive all required Vitamin B12 from the diet.
2.4 mcg. Some literature says 6 mcg.
Vitamin B12 deficiency can cause fatigue. Some research indicates that people who are not deficient can take the vitamin to increase energy. Since Vitamin B12 comes from animal sources, vegetarians are at high risk for Vitamin B12 deficiency. Others who should take Vitamin B12 include people who have pernicious anemia, people who have gastrointestinal disorders and older adults.
Low levels of B-12 can cause anemia as well as numbness or tingling in the extremities or other neurological symptoms
Vitamin B12 has a very low likelihood for toxicity.
Beware! Folic acid can correct the anemia associated with Vitamin B12 deficiency, but will not correct the nerve damage associated with Vitamin B12 deficiency. Vitamin B12 deficiency can cause permanent nerve damage. Therefore, it is wise to be tested for Vitamin deficiency before taking folic acid (or I would go so far as to say, you should simply take Vitamin B12 along with your folic acid supplement).
Liver, beef, fish and seafood, cereals, and dairy products are good sources.
Vitamin B12 can treat pernicious anemia, depression, Crohn's disease and high homocysteine levels. It is also helpful for treating high cholesterol, asthma, diabetes, chronic fatigue syndrome, and Alzheimer's disease, among others.
Antacids will impede absorption of Vitamin B12, because they minimize the stomach acid required to break down the vitamin. Antibiotics and certain HIV drugs may also block absorption of Vitamin B12.
Tripathi M, Sheshadri S, Padma MV, Jain S, Meheshwari MC, Behari M.
Serum cobalamin levels in dementias.
Neurol India. 2001 Sep;49(3):284-6.
Alzheimer's patients were found to have reduced serum B-12 levels.