|Molecular mass||1355.37 g/mol|
|Disclaimer and references|
Vitamin B12 is a water-soluble vitamin that abides in various different forms, and is a part of the vitamin B-complex. There are two main forms of B12 that are used in human metabolism: Methylcobalamin and 5-Deoxyadenosylcobalamin. It contains the mineral cobalt, and therefore compounds that have vitamin B12 are generally called "cobalamins."
It naturally exists in some foods, can be added to others, and is accessible as a dietary supplement. It is required for many things connecting with human health. It is essential in red-blood cell maintenance, neurological function, and DNA synthesis. B12 is also extremely essential in cases of preventing Pernicious anemia which is an autoimmune disease that impacts the gastric mucosa. This will then lead to gastric atrophy which can end up fatal. Regular anemia can lead to neurological disorders even if it is in the presence of vitamin B12.  B12 is also known as the "red vitamin" because of it's make-up, which is of a red crystalline compound. It is the only known supplement that contains cobalt. 
Vitamin B12 is the only discovered indispensible biomolecule with a stable metal-carbon bond. It is an organometallic compound. The carbon from the bond can link to various things:
- It can link to a methyl group – as in methylcobalamin.
- It can link to a 5’-deoxyadenosine at the 5’ position – as in adenosylcobalamin.
- It can also link to a cyanide group as in Vitamin B12.
The marrow of the molecule consists of a corrin ring, that has several fused sidegroups. The ring has four pyrrole subunits that are connected on opposite ends through a C-CH3 methylene link, then on one side connected through a C-H methylene link. This causes two of the pyrroles to join directly. This creates a similarity between this and a porphyrin, except with one of the bonds between a methylene group removed. Then the nitrogen of each pyrrole is correlated to the primary cobalt atom. The remaining nitrogen is connected to a five-carbon sugar, which in time will connect to a phosphate group. Then it will connect back onto the corrin ring, which is also known as one of the seven amide groups that is connected to the outer edges of the corrin ring. Then the base ligand will form a strap that connects back onto the corrin ring.
In importance to the corrin ring, when being compared to the porphyrin, is the flexibility of the corrin system. The ring is also slighter thicker when observed from the side in comparison to the porphyrin ring. Also, the corrin only has a conjugated chain that goes around the ring system. However, a porphyrin ring has a chain that is restricted around all four pyrolle rings. 
Vitamin B12 has many functions, each essential to the daily needs of the human body. It's central functions are in the development of red blood cells and the preservation of a robust nervous system. It is needed for the swift synthesis of DNA during the cell divison. This is crucial and extremely important in tissues where the cells are bisecting quickly; specifically in the bone marrow tissues that are primarily responsible for the red blood cell development. When Vitamin B12 deficiency takes place, DNA production is impeded and abnormal cells also known as megaloblasts are formed. This will result in anemia. Various symptoms of anemia are: experiencing breathlessness, excessive fatigue, feeling listless, and poor defenses against bacteria, also known as a weakened immune system. 
B12 is also key in conserving the nervous system. Nerves are enclosed by a fatty casing composed of an elaborate protein called myelin. B12 is essential because it plays a critical part in the metabolism of fatty acids that are imperative for the keeping of myelin. If vitamin B12 deficiency is extended, this can cause swift nerve degeneration and irreversible neurological damage. 
B12 deficiency is due most likely connected to a failed attempt in trying to absorb B12 from the intestine instead of a dietary deficiency. The process of absorbing B12 involves the secretion of cells lining the stomach of a glycoprotein, commonly known as the intrinsic factor. The B12 secretion is then absorbed in the ileum in the existence of calcium. However, some people are unable to produce intrinsic factor and must have their anemia treated with B12 injections. Vitamin B12 is stored in small areas throughout the body. The total body storage amount in adults is 2 to 5 mg. Approximately eighty percent of this is stored in the liver. 
The bile excretes Vitamin B12 and effectively reabsorbs it. This cycle is referred to as the enterohepatic circulation. The bile can excrete various amounts of vitamin B12; the amounts range from one to ten micrograms per day. Some people who have diets that are low in B12 such as Vegans and Vegetarians, are most likely getting their B12 from reabsorption rather than from dietary sources. Due to the process of reabsorption, it is possible to take up to twenty years for any sort of deficiency disease to take place in people whose diets have changed and are now absent in B12. 
The discovery of vitamin B12 occurred in two different places, the United States and in England. Researchers around the globe were trying to find a compound that would successfully treat anemia. Until the early 1900's, anyone who had anemia has only the slightest chance of surviving it. However two physicians determined to put a stop to the fatal disease, George Richards Minot and William Perry Murphy followed the studies of George Whipple and found that a daily diet of around a pound of liver would be able to control the fatal anemia. Because of their determination and hard work, Both Minot and Murphy along with Whipple all received the Nobel Prize in medicine and physiology.
Afterwards, scientists and researchers all around were trying to seclude the "active principle" in liver that stopped anemia. However, this progress was very lengthy. Many years went by and Karl Folkers, an American chemist had been leading a research team trying to find a solution. Then finally in 1948, the group finally discovered a resolution. They discovered that they could measure the vitamin indirectly by measuring the bacteria that needed vitamin B12 to grow. Afterwards, several members of the research team discovered a way to purify B12 into minute red crystals. However at almost the same time, E. Lester Smith and L.F.S. Parker from England announced the same discovery. After more extensive research, scientists found that the vitamin proved to be a very big and complex molecule. It's structure was only able to be figured out after the help of advanced technology. 
A deficiency in vitamin B12 shows that your body is lacking in this vitamin and can result in anemia. Anemia is an disease in which your body is running low on red blood cells. When one's body is running low on red blood cells, there is less oxygen that is being carried and distributed around your body. This will result in weakness and fatigue. Many people however, are able to get the vitamin easily through eating things such as eggs, dairy, and meat. The deficiency mostly occurs when the digestive system is having difficulty absorbing the vitamin.  There are typically three things that can cause deficiency:
- When someone has pernicious anemia which is when one's body becomes self-destructive and ruins the cells in your stomach that are meant for absorbing B12.
- If a surgery has taken place where part of the stomach or the last part of the intestine has been taken out. This is also a type of fat-reduction process that obese people use to lose weight.
- There is a problem with the way one's body digests food, Chron's disease, if there is bacteria growth in the intestine, or a parasite. 
Symptoms of deficiency
There are various symptoms that could prove B12 deficiency in the system. Sometimes the symptoms might be so light that someone might not even notice them.
- Fatigue, weakness, light-headedness
- Pale/lightened skin
- Sore, red, swollen gums or tongue
- Nausea and increase in weight loss
- Diarrhea or constipation
B12 Dietary Sources
If one is looking for a source where they can find B12 naturally, it is mostly found in animal products such as: fish, meat, poultry, eggs, milk, and dairy products. These are the only trustworthy and unfortified sources of B12.  Vitamin B12 is not typically found in plant foods. However, fortified breakfast cereals are an easy and very available source with high vitamin B12. Also, some yeast products also contain high doses of B12.  Some scientists and researchers, with further study, have found that some claimed B12 supplements, actually may in fact increase your risk of B12 deficiency disease. Scientists found that the B12 analogues can compete with B12 and impede metabolism.  B12 is also known for it's extensive relationship with folic acid. Both play vital roles in the metabolism process. B12 labors to reactivate and revive folic acid; while folic acid works to keep the balance for both B12 and itself. When B12 deficiency takes place, following swiftly come folic acid deficiency. Folic acid is needed for the consistent production of red blood cells. The less folic acid in the body, the less red blood cells are produced.
Vitamin B12 usually exists as cyanocobalamin in dietary supplements. Cyanocobalamin is a form that the body easily transfigures to the active forms methylcobalamin and 5-deoxyadenosylcobalamin. Some dietary supplements also are able to withhold methylcobalamin, and other various arrangements of B12. Evidence today does not show any differences among the different forms of either absorption or bioavailability. Nonetheless, being able to absorb vitamin B12 from dietary supplements is hugely constricted because of it's limitation from the intrinsic factor. 
For prescription medications of B12, it comes in the forms of cyanocobalamin and once in a while, hydroxocobalamin. It can be given through an administrator as a prescription, and this usually happens through an intramuscular injection. Paranteral administration means that it is commonly used to treat the B12 deficiency that is based from pernicious anemia and other sicknesses that result in B12 malabsorption or severe deficiency. The B12 prescription medicine can also come in a gel formulation that is required to be applied intranasally. This offers as a replacement for those who need B12 injections but prefer the gel formulation better. 
- Dietary Supplement: Vitamin B12 By Office of Dietary Supplements
- Vitamin B12 with Folic Acid Dietary Supplement By Len7288 on Hub pages
- Structural detail for Vitamin B12 By University of Bristol, School of Chemistry
- B12 Information Sheet By The Vegetarian Society
- Vitamin B12 By World of Scientific Discovery
- Vitamin B12 Deficiency Anemia By Web MD