VITAMIN B 12 (CYANOCOBALAMIN)

Vitamin B12
Helps in DNA synthesis.
Vitamin B 12 is produced by the natural bacterial flora of animals and is believed to be obtained in the diet only from consumption of animal products.
Deficiency of vitamin B 12 occurs in several settings. Insufficient dietary intake occurs among alcoholics.
Malabsorption occurs when gastric synthesis of intrinsic factor is impaired, such as in a disease called autoimmune pernicious anemia or following stomach surgery.
intestinal absorption of vitamin B 12 may be decreased by tropical sprue, Crohn's disease, Zollinger-Ellison's syndrome, and Whipple's disease.
Alterations of gut flora, especially those caused by infection with Diphyllobothrium latum, reduce vitamin B 12 absorption.
Congenital lack of transcobalmin II, a B 12 transport protein, has been reported.
Because body stores of vitamin B 12 are large (4 mg) relative to the minimum daily requirement (2.5 µg), a deficiency state must persist for 3 to 6 years before symptoms develop.
The predominant cutaneous manifestation of vitamin B 12 deficiency is the development of generalized hyperpigmented macules and patches. These favor the skin of flexural areas, palmar creases, soles, knuckles, and oral mucosa. Nail plates develop longitudinal, hyperpigmented streaks. The hair may turn gray.
Vitamin B 12 deficiency caused by pernicious anemia is associated with vitiligo and alopecia areata.
The tongue may be beefy red and may burn
Systemic findings in vitamin B 12 deficiency include macrocytic anemia and occasional heart symptoms.
Synthesis of myelin is impaired, causing paresthesias, numbness of the extremities, ataxia, altered reflexes, and changes in mental status. If the deficiency is not corrected, serious degeneration may occur in the dorsal columns of the spinal cord.
Treatment with parenteral cyanocobalamin (1 mg per week for a month and then 1 mg per month thereafter) reduces fatigue in several days, corrects anemia in weeks, and reverses cutaneous changes in 1 year. Neurologic symptoms may resolve or persist.