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Vitamin B12

Vitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin that has a key role in the normal functioning of the brain and nervous system, and the formation of red blood cells. It is one of eight B vitamins. It is involved in the metabolism of every cell of the human body, especially affecting DNAsynthesis, fatty acid and amino acid metabolism.

Neither fungi, plants, nor animals (including humans) are capable of producing vitamin B12. Only bacteria and archaeahave the enzymes needed for its synthesis. Some plant foods are a natural source of B12 because of bacterial symbiosis. B12 is the largest and most structurally complicated vitamin and can be produced industrially only through a bacterial fermentation-synthesis. This synthetic B12 is used to fortify foods and sold as a dietary supplement.

Vitamin B12 consists of a class of chemically related compounds (vitamers), all of which show pharmacological activity. It contains the biochemically rare element cobalt(chemical symbol Co) positioned in the center of a planar tetra-pyrrole ring called a corrin ring. The vitamer is produced by bacteria as hydroxocobalamin, but conversion between different forms of the vitamin occurs in the body after consumption.

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A common synthetic form of the vitamin is cyanocobalamin, produced by chemically modifying bacterial hydroxocobalamin. Because of superior stability and low cost this form is used in many pharmaceuticals and supplements as well as for fortification of foods. In the body it is converted into the human physiological forms methylcobalaminand 5′-deoxyadenosylcobalamin. In this process a cyanide ion, (CN), is produced, but the amount is very, very small (20 μg from 1,000 μg of cyanocobalamin) compared to what would cause a toxicity risk, and is in fact less than the amount of cyanide consumed daily from food (primarily fruit, nuts, seeds, legumes). Cyanide-free synthetic forms of the vitamin—hydroxocobalamin, methylcobalamin, and adenosylcobalamin—are being used in some pharmacological products and supplements, but their claimed superiority to cyanocobalamin is debatable.

Supplements of this B vitamin have been shown to be effective in pain management for a variety of conditions, including low-back pain and recurrent aphthous stomatitis, or mouth sores. Most people get enough B12 from their diet through animal products, such as eggs, milk, fish, and meat, and some fortified cereals . Vegans and some vegetarians should take B12 supplements to replace what they are not getting through their diet, but taking supplements beyond the recommended daily allowance of 2.4 micrograms for most adults is not suggested because a safe upper limit has not been established.

Vitamin B12 was discovered from its relationship to the disease pernicious anemia, an autoimmune disease in which parietal cells of the stomach responsible for secretingintrinsic factor are destroyed; these cells are also responsible for secreting acid in the stomach. Because intrinsic factor is crucial for the normal absorption of B12, its lack in the presence of pernicious anemia causes a vitamin B12 deficiency. Many other subtler kinds of vitamin B12 deficiency and their biochemical effects have since been elucidated.

How much vitamin B12 do I need?

The amount of vitamin B12 you need each day depends on your age. Average daily recommended amounts for different ages are listed below in micrograms (mcg):

Life Stage Recommended Amount
Birth to 6 months 0.4 mcg
Infants 7–12 months 0.5 mcg
Children 1–3 years 0.9 mcg
Children 4–8 years 1.2 mcg
Children 9–13 years 1.8 mcg
Teens 14–18 years 2.4 mcg
Adults 2.4 mcg
Pregnant teens and women 2.6 mcg
Breastfeeding teens and women 2.8 mcg

 

What foods provide vitamin B12?

Vitamin B12 is found naturally in a wide variety of animal foods and is added to some fortified foods. Plant foods have no vitamin B12 unless they are fortified. You can get recommended amounts of vitamin B12 by eating a variety of foods including the following:

  • Beef liver and clams, which are the best sources of vitamin B12.
  • Fish, meat, poultry, eggs, milk, and other dairy products, which also contain vitamin B12.
  • Some breakfast cereals, nutritional yeasts and other food products that are fortified with vitamin B12. To find out if vitamin B12 has been added to a food product, check the product labels.

Am I getting enough vitamin B12?

Most people in the United States get enough vitamin B12 from the foods they eat. But some people have trouble absorbing vitamin B12 from food. As a result, vitamin B12 deficiency affects between 1.5% and 15% of the public. Your doctor can test your vitamin B12 level to see if you have a deficiency.

Certain groups may not get enough vitamin B12 or have trouble absorbing it:

  • Many older adults, who do not have enough hydrochloric acid in their stomach to absorb the vitamin B12 naturally present in food. People over 50 should get most of their vitamin B12 from fortified foods or dietary supplements because, in most cases, their bodies can absorb vitamin B12 from these sources.
  • People with pernicious anemia whose bodies do not make the intrinsic factor needed to absorb vitamin B12. Doctors usually treat pernicious anemia with vitamin B12 shots, although very highoral doses of vitamin B12 might also be effective.
  • People who have had gastrointestinal surgery, such as weight loss surgery, or who have digestive disorders, such as celiac disease or Crohn’s disease. These conditions can decrease the amount of vitamin B12 that the body can absorb.
  • Some people who eat little or no animal foods such as vegetarians and vegans. Only animal foods have vitamin B12 naturally. When pregnant women and women who breastfeed their babies are strict vegetarians or vegans, their babies might also not get enough vitamin B12.

 

What happens if I don’t get enough vitamin B12?

Vitamin B12 deficiency causes tiredness, weakness, constipation, loss of appetite, weight loss, and megaloblastic anemia.  Nerve problems, such as numbness and tingling in the hands and feet, can also occur. Other symptoms of vitamin B12 deficiency include problems with balance, depression, confusion, dementia, poor memory, and soreness of the mouth or tongue. Vitamin B12 deficiency can damage the nervous system even in people who don’t have anemia, so it is important to treat a deficiency as soon as possible.

In infants, signs of a vitamin B12 deficiency include failure to thrive, problems with movement, delays in reaching the typical developmental milestones, and megaloblastic anemia.

Large amounts of folic acid can hide a vitamin B12 deficiency by correcting megaloblastic anemia, a hallmark of vitamin B12 deficiency. But folic acid does not correct the progressive damage to the nervous system that vitamin B12 deficiency also causes. For this reason, healthy adults should not get more than 1,000 mcg of folic acid a day.

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