What Is It
Also known as cobalamin, vitamin B12 was the last vitamin to be discovered. In the late 1940s it was identified as the substance in calf's liver that cured pernicious anemia, a potentially fatal disease primarily affecting older adults. Vitamin B12 is the only B vitamin the body stores in large amounts, mostly in the liver. The body absorbs B12 through a very complicated process: Digestive enzymes in the presence of enough stomach acid separate B12 from the protein in foods. The vitamin then binds with a substance called intrinsic factor (a protein produced by cells in the stomach lining) before being carried to the small intestine, where it is absorbed. Low levels of stomach acid or an inadequate amount of intrinsic factor-both of which occur with age-can lead to deficiencies. However, because the body has good reserves of B12, it can take several years for a shortfall to develop.
What Does It Do
Vitamin B12 is essential for cell replication and is particularly important for red blood cell production. It maintains the protective sheath around nerves (myelin), assist in converting food to energy, and plays a critical role in the production of DNA and RNA, the genetic material in cells.
• Prevents a form of anemia.
• Helps reduce depression.
• Thwarts nerve pain, numbness, and tingling.
• Lowers the risk of heart disease.
• May improve multiple sclerosis and tinnitus.
Moderately high blood levels of homocysteine, an amino acid-like substance, have been linked to an increased risk of heart disease. Working with folic acid, vitamin B12 helps the body process homocysteine and so may lower that risk. Because of its beneficial effects on the nerves, vitamin B12 may help prevent a number of neurological disorders, as well as the numbness and tingling often associated with diabetes. It may also play a part in treating depression.
Research shows that low levels of vitamin B12 are common in people with Alzheimer's disease. Whether this deficiency is a contributing factor to the disease or simply a result of it is unknown. The nutrient does, however, keep the immune system healthy. Some studies suggest that it lengthens the amount of time between infection with the HIV virus and the development of AIDS. Other research indicates adequate B12 intake improves immune responses in older people. With its beneficial effect on nerves, vitamin B12 may lessen ringing in the ears (tinnitus). As a component of myelin, it is valuable in treating multiple sclerosis, a disease that involves the destruction of this nerve covering. And through its role in cell replication, B12 may improves symptoms of rosacea.
How Much You Need
The RDA for vitamin B12 is 2.4 mcg a day for adults. But, many experts recommend that you get 100 to 400 mcg. Supplements of vitamin B12 are very important for older people and vegans (who eat no meat products).
If You Get Too Little: Symptoms of a vitamin B12 deficiency include fatigue, depression, numbness and tingling in the extremities caused by nerve damage, muscle weakness, confusion, and memory loss. Dementia and pernicious anemia can develop; both are reversible if caught early.
The level of B12 in the blood decreases with age. People with ulcers, Crohn's disease, or other gastrointestinal disorders are at risk, as are those taking prescription medication for epilepsy (seizures), chronic heartburn, or gout. Excessive alcohol also hinders absorption of vitamin B12.
If You Get Too Much: Excess vitamin B12 is readily excreted in urine; there are no known adverse side effects from a high intake of vitamin B12.
How To Take It
Dosage: A general dose of 1,000 mcg of vitamins B12 a day is useful for heart disease prevention, pernicious anemia, numbness and tingling, tinnitus, multiple sclerosis, and roseacea. If you're deficient in B12, higher doses may be needed. Or if you do not produce enough intrinsic factor, B12 shots or a prescription nasal spray may be necessary; ask your doctor.
Guidelines For Use: Take vitamin B12 once a day, preferably in the morning, along with at least 400 mcg of folic acid. Most multivitamins contain at least the RDA of vitamin B12 and folic acid; B-complex supplements have higher amounts. For larger therapeutic amounts, look for a supplement with just vitamin B12 or B12 with folic acid. Using a sublingual (under-the-tongue) form enhances absorption.
Animal foods are the primary source of B12. These include organ meats, brewer's yeast, oysters, sardines and other fish, eggs, meat, and cheese. Some breakfast cereals are fortified with this vitamin as well.
If you take a vitamin B12 supplement, you must also have a folic acid supplement: A high intake of one can mask a deficiency of the other.
• Having a sufficient amount of vitamin B12 in the body may slow the progression of HIV infection to AIDS, according to a study of 310 HIV-positive men. On average, those with low B12 levels developed AIDS within four years of the start of the study, versus eight years in men who had higher B12 levels.
• Older people who have mildly low vitamin B12 levels may not get the full protection from a pneumonia vaccine. In a study of 30 elderly people, those with inadequate B12 stores produced fewer antibodies to the virus that causes pneumonia after vaccination than those with sufficient levels of B12. This low response would reduce their ability to fight off the disease.