Vitamin B12 is a water-soluble vitamin that exists in several cobalt containing forms .These compounds showing vitamin B12 activity are known as cobalamines. It has a complex structure made up of a tetrayrrole ring system called a corrin ring with a central cobalt atom. An R group is attached to the central cobalt atom which gives the various forms of vitamin B12. A cyanide R group forms cyanocobalamin, hydroxyl R group forms hydroxyl cobalamin, a methyl R group forms methyl cobalamine, and a deoxyadenosine R group forms deoxyadenosyl cobalamin. All these exhibit vitamin B12 activity. Mammals are unable to synthesize cobalamins and as such are obtained from the diet. Any excess amount is usually excreted in urine hence vitamin B 12 toxicity is rare.
Vitamin B12 functions as a prosthetic group or coenzyme. Humans and other higher animals require vitamin B 12 for two enzymes; methionine synthase and methymalonyl-coA mutase (MCM). For instance, methyl cobalamine is involved in the synthesis of purines and pyrimidines by methionine synthase. Another function conferred by methionine synthetase is the formation of phospholipids and neurotransmitters hence enabling proper functioning of the neurological system. Its role in the formation of myelin also aids in the normal functioning of the brain and the nervous system. Therefore, a deficiency in vitamin B12 results in neurological disturbances or paraesthesia or in extreme cases degeneration of the spinal cord.
Vitamin B 12 is also essential for the rapid DNA production during the process of cell division. This plays a crucial in the synthesis of blood cells in the bone marrow where the cells divide rapidly. In absence of B12, the synthesis of DNA is interfered with and as a result abnormal cells known as megaloblasts are produced during red blood cell formation. Therefore, vitamin B12 is essential in the formation of healthy blood cells so that they multiply and develop properly.
It also functions to lower the plasma concentration of homocsyteine that is crucial for effective cardiac function. Vitamin B 12 is crucial coenzyme in the conversion of homocsyteine into methionine. Elevated levels are a risk factor for improper cardiac function as it promotes atherosclerosis.
Vitamin B 12 plays a role in cellular energy production. It is involved in the metabolism as it is involved in fatty acid synthesis hence enabling the release of energy by the body. In addition, it is involved the absorption of folic acid that is required for effective neurological function. Vitamin B 12 also plays a role in the normal structure and functioning of nerves.
Vitamin B 12 deficiency is common due to the limited dietary intake of animal foods. Research in the United States depicts that about 1.5-15% of the population are diagnosed with vitamin B12 deficiency. Vitamin B12 deficiency affects the bone marrow, intestinal tract, and the neurological system. The deficiency could be as a result of inadequate intake especially in vegetarians or lack of intrinsic factor a substance that aids its absorption. Some drugs such as colchicine, salicylates, and neomycin can also induce vitamin B12 deficiency by interacting with intrinsic factor. This leads to the development of pernicious anemia. Above all, prolonged alcohol consumption can also impair the absorption of vitamin B12. This affects the hematopoietic system, the gastrointestinal system, and nervous system.
The daily requirement of vitamin B12 in adults is up to 3-4 micrograms per day. Vitamin B12 is mainly extracted from animal sources such as kidney, liver, brain, meat, fish, and eggs. The fact that it is absent from animal sources makes vegetarians vulnerable to vitamin B12 deficiency.