Vitamin B12, also known as cobalamin, is a water-soluble vitamin essential for hematopoietic and neurological functions in the body. It is obtained primarily from animal sources such as meat and fish. Many breakfast cereals and nondairy beverages such as soymilk are fortified with vitamin B12. When vitamin B12 from animal foods enters the stomach it is protein bound and must be released by the action of pepsin in the stomach. It is then attached to R-proteins and is transported through the duodenum where it is hydrolyzed and free cobalamin is released. Cobalamin requires intrinsic factor (IF) to attach to it, in order to be absorbed in the terminal ileum. This absorption process is calcium mediated and is the most probable opportunity for met formin induced vitamin B12 deficiency. Adding supplemental calcium has been shown to mediate the deficiency in some cases though there is not enough evidence to recommend calcium supplementation as an effective preventative measure.
Vitamin B12 is an essential cofactor in the conversion of homocysteine to methionine and regeneration of folate. This is a key step in the metabolic process that leads to DNA synthesis and formation and protection of the myelin sheath. Demyelination of nerve endings can lead to peripheral neuropathy. Symptoms begin to manifest as numbness and paresthesia in the feet. This tingling feeling is caused by pressure on the nerves. If the vitamin B12 deficiency is not corrected, weakness, ataxia, sphincter disturbance, and changes in mental status will follow.
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