Vitamin B 12also called cobalaminis a water-soluble vitamin that is involved in the metabolism of b vitamin and heart health cell of b vitamin and heart health human body: Vitamin B ceramics and sculpture lessons plans is one of eight B vitamins ; it is the largest and most structurally complicated vitamin.
It consists of a class of chemically related compounds vitamersall of which show physiological activity. It contains the biochemically rare element cobalt chemical symbol Co positioned in the center of a corrin ring. The only organisms to produce vitamin B 12 are certain bacteriaand archaea. Some of these bacteria are found in the soil around the grasses that ruminants eat; they are taken into the animal, proliferate, form part of their gut floraand continue to produce vitamin B There are no naturally-occurring notable vegetable dietary sources of the vitamin, so vegans and vegetarians are advised   to take a supplement or fortified foods.
Otherwise, most omnivorous people in developed countries obtain enough vitamin B 12 from consuming b vitamin and heart health products including meat, milk, eggs, and fish.
Vitamin B 12 supplements are available in single agent or multivitamin tablets; and pharmaceutical preparations may be given by intramuscular injection. The most common cause of vitamin B 12 deficiency in developed countries is impaired absorption due to a loss of gastric intrinsic factorwhich must be bound to food-source B 12 in order for absorption to occur. Another group affected are those on long term antacid therapy,  using proton pump inhibitorsH2 blockers or other antacids.
This condition may be characterised by limb neuropathy or a blood disorder called pernicious anemiaa type of megaloblastic anemia. Folate levels in the individual may affect the course of pathological changes and symptomatology.
Deficiency is more likely after age 60, and increases in incidence with advancing age. Other causes of vitamin B 12 deficiency are much less frequent. Vitamin B 12 is produced industrially via bacterial fermentation. Vitamin B 12 total synthesis has been achieved, b vitamin and heart health, but has no practical value. Vitamin B 12 was discovered as a result of its relationship to pernicious anemia.
B 12 is the most chemically complex of all the vitamins. The structure of B 12 is based on a corrin ring, which is similar to the porphyrin ring found in heme. The central metal ion is cobalt. B vitamin and heart health of the six coordination sites are provided by the corrin ring, b vitamin and heart health, and a fifth by a dimethylbenzimidazole group.
Historically, the covalent C-Co bond is one of the first examples of carbon-metal bonds to be discovered in biology, b vitamin and heart health. The hydrogenases and, by necessity, enzymes associated with cobalt utilization, involve metal-carbon beans and weight loss. Vitamin B 12 is a generic descriptor name referring to a collection of cobalt and corrin ring molecules which are defined by their particular vitamin function in the body.
All of the substrate cobalt-corrin molecules from which B 12 is made must be synthesized by bacteria. After this synthesis is complete, the human body has the ability except in rare cases to convert any form of B 12 to an active form, b vitamin and heart health, by means of enzymatically removing certain prosthetic chemical groups from the cobalt atom and replacing them with others.
The four vitamers of B 12 are all deeply red colored crystals and water solutions, b vitamin and heart health, due to the color of the cobalt-corrin complex.
The current EAR for vitamin B 12 for women and men ages 14 and up is 2. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy equals 2. RDA for lactation equals 2, b vitamin and heart health. For infants up to 12 months the Adequate Intake AI is 0. For children ages 1—13 years the RDA increases with age from 0. Because 10 to 30 percent of older people may be unable to effectively absorb vitamin B 12 naturally occurring in foods, it is advisable for those older than 50 years to meet their RDA mainly by consuming foods fortified with vitamin B 12 or a supplement containing vitamin B In the case of vitamin B 12 there is no UL, as there is no human data for adverse effects from high doses.
For women and men over age 18 the Adequate Intake AI is set at 4. AI for pregnancy is 4. For children aged 1—17 years the AIs increase with age from 1.
These AIs are higher than the U. The original deadline to be in compliance was July 28,but on September 29, the FDA released a proposed rule that extended the deadline to January 1, for large companies and January epsom salt bath and hair loss, for small companies.
Most omnivorous people in developed countries obtain enough vitamin B 12 from consuming animal products including, meat, fish, eggs, and milk. B 12 is only produced in nature by certain bacteriaand archaea. Feces are a rich source of vitamin B 12and are eaten by many animals, b vitamin and heart health, including dogs and cats.
These animals ingest cecotropes which have been expelled in their feces. Animals store vitamin B 12 in liver and muscle and some pass the vitamin into their eggs and milk ; meat, liver, eggs and milk are therefore sources of the vitamin for other animals as well as humans.
Natural sources of B 12 include dried and fermented plant foods, such as tempehand lavera seaweed. The UK Vegan Societythe Vegetarian Resource Group, and the Physicians Committee for Responsible Medicineamong others, recommend that every vegan who is not consuming adequate B 12 from fortified foods take supplements.
Foods for which B 12 -fortified versions are widely available include breakfast cerealsb vitamin and heart health, soy products, energy barsand nutritional yeast.
Vitamin B 12 is included in multivitamin pills; and in some countries grain-based foods b vitamin and heart health as bread and b vitamin and heart health are fortified with B The vitamin can also be a prescription product via injection or other means.
Sublingual methylcobalaminwhich contains no cyanideis available in 5-mg tablets. The metabolic fate and biological distribution of methylcobalamin are expected to be similar to that of other sources of vitamin B 12 in the diet. Injection and patches are sometimes used if digestive absorption is impaired, but this course of action may not be necessary with high-potency oral supplements such as 0.
Even pernicious anemia can be treated entirely by the oral route. If the person has inborn errors in the methyltransfer pathway cobalamin C disease, combined methylmalonic aciduria and homocystinuriatreatment with intravenous, intramuscular hydroxocobalamin or transdermal B 12 is needed. Pseudovitamin-B 12 refers to B 12 -like analogues that are biologically inactive in humans and yet found birth control and depression be present alongside B 12 in humans,  many food sources including animals and possibly supplements and fortified foods.
Vitamin B 12 functions as a coenzymemeaning that its presence is required for enzyme-catalyzed reactions. In humans, two major coenzyme B 12 b vitamin and heart health enzyme families corresponding to the first two reaction types, are known. These are typified by the following two enzymes:. If folate is present in quantity, then of the two absolutely vitamin B 12 -dependent enzyme-family reactions in humans, the MUT -family reactions show the most direct and characteristic secondary effects, focusing on the nervous system see below.
This is because the MTR methyltransferase-type reactions are involved in regenerating folate, and thus are less evident when folate is in good supply. Since the late s, folic acid has begun to be added to fortify flour in many countries, so folate clotrimazole and betamethasone diproprionate cream is now more rare.
At the same time, since DNA synthetic-sensitive tests for anemia and erythrocyte size are routinely done in even simple medical test clinics so that these folate-mediated biochemical effects are more often directly detectedthe MTR -dependent effects of B 12 deficiency are becoming apparent not as anemia due to DNA-synthetic problems as they were classicallybut now mainly as a simple and less obvious elevation of homocysteine in the blood and urine homocysteinuria.
This condition may result in long-term damage to arteries and in clotting stroke and heart attackbut this effect is difficult to separate from other common processes associated with atherosclerosis and aging. The specific myelin damage resulting from B 12 deficiency, even in the presence of adequate folate and methionine, is more specifically and clearly a vitamin deficiency problem.
It has been connected to B 12 most directly by reactions related to MUT, which is absolutely required to convert methylmalonyl coenzyme A into succinyl coenzyme A.
Failure of this second reaction to occur results in elevated levels of MMA, b vitamin and heart health, a myelin destabilizer. Excessive MMA will prevent normal fatty acid synthesisor it will be incorporated into fatty acids itself rather than normal malonic acid.
If this abnormal fatty acid subsequently is incorporated into myelin, the resulting myelin will be too fragile, and demyelination will occur. Although the precise mechanism or mechanisms are not known with certainty, the result is subacute combined degeneration of spinal cord.
Vitamin B 12 -dependent MTR reactions may also have neurological effects, through an indirect mechanism. Adequate methionine which, like folate, must otherwise be obtained in the diet, if it is not regenerated from homocysteine by a B 12 dependent reaction is needed to make S -adenosyl methionine SAMewhich is in turn necessary for methylation of myelin sheath phospholipids.
Although production of SAMe is not B 12 dependent, help in recycling for provision of one adequate substrate for it the essential amino acid methionine is assisted by B In addition, SAMe is involved in the manufacture of certain neurotransmitterscatecholamines and in brain metabolism. These neurotransmitters are important for maintaining mood, possibly explaining why depression is associated with B 12 deficiency.
Methylation of the myelin sheath phospholipids may also depend on adequate folate, which in turn is dependent on MTR recycling, unless ingested in relatively high amounts. Methyl-B 12 is absorbed by two processes. The first is an intestinal mechanism using intrinsic factor through which 1—2 micrograms can be absorbed every few hours.
Protein-bound vitamin B 12 must be released from the proteins by the action of digestive proteases in both the stomach and small intestine. B 12 taken in a low-solubility, non-chewable supplement pill form may bypass the mouth and stomach and not mix with gastric acids, but acids are not necessary for the absorption of free B 12 not bound to protein; acid is necessary only to recover naturally-occurring vitamin B 12 from foods. R-protein also known as haptocorrin and cobalophilin is a B 12 binding protein that is produced in the salivary glands.
It must wait to bind food-B 12 until B 12 has been freed from proteins in food by pepsin in the stomach. B 12 then binds to the R-protein to avoid degradation of it in the acidic environment of the stomach. This pattern of B 12 transfer to a special binding protein secreted in a previous digestive step, is repeated once more before absorption.
The next binding protein for B 12 is intrinsic factor IFa protein synthesized by gastric parietal cells that is secreted in response to histaminegastrin and pentagastrinas well as the presence of food.
B 12 must be attached to IF for it to be efficiently absorbed, as receptors on the enterocytes in the terminal ileum of the small bowel only recognize the B 12 -IF complex; in addition, intrinsic factor b vitamin and heart health the vitamin from catabolism by intestinal bacteria.
Absorption of food vitamin B 12 thus requires an intact and functioning stomachexocrine pancreasintrinsic factor, and small bowel. Problems with any one of these organs makes a vitamin B 12 deficiency possible.
Individuals who lack intrinsic factor have a decreased ability to absorb B In pernicious anemiab vitamin and heart health, there is a lack of IF due to autoimmune atrophic gastritisb vitamin and heart health, in which antibodies form against parietal cells. Antibodies may alternately form against and bind to IF, inhibiting it from carrying out its B 12 protective function. Due to the complexity of B 12 absorption, geriatric patients, many of whom are hypoacidic due to reduced parietal cell function, have an increased risk of B 12 deficiency.
Hereditary defects in production of the transcobalamins and their receptors b vitamin and heart health produce functional deficiencies in B 12 and infantile megaloblastic anemiaand abnormal B 12 related biochemistry, even in some cases with normal blood B 12 levels, b vitamin and heart health. The transcobalamin-II is degraded within a lysosomeand free B 12 is finally released into the cytoplasm, where it may be transformed into the proper coenzyme, by certain cellular enzymes see above.
Investigations into the intestinal absorption of B 12 point out that the upper limit of absorption per single oral dose, under normal conditions, is about 1. In a similar study Swendseid et al.
It is this last fact which allows pernicious anemia and certain other defects in B 12 b vitamin and heart health to be treated with oral megadoses of B 12even without any correction of the underlying absorption defects. B vitamin and heart health is the main form of B 12 excretion; most of the B 12 secreted in the bile b vitamin and heart health recycled via enterohepatic circulation.