Vitamin B12, also called cobalamin, plays a role in regulating nervous system function, general cell metabolism, DNA synthesis and red blood cell production. The most severe form of vitamin B12 deficiency causes pernicious anemia, a blood disorder characterized by markedly reduced red blood cell counts, gastrointestinal problems and neurological disorders. This type of deficiency occurs only in people with an autoimmune disease that kills the cells in the stomach that secrete proteins necessary for B12 absorption. Milder forms of vitamin B12 deficiency are caused dietary insufficiency and stomach disorders that reduce gastric acid production and decrease B12 absorption. The Office of Dietary Supplements, or ODS, indicates that a doctor diagnoses a deficiency when your blood levels of B12 fall below 250 pg/mL.
Cognitive Problems
Vitamin B12 deficiency can contribute to neuron damage in the central nervous system, resulting in depression, memory impairment and dementia. An article in the "Journal of Neuropsychiatry and Clinical Neurosciences" reports that vitamin B12 deficiency has been linked to Alzheimer's disease and other cognitive impairments. The authors note that successful reversal of neurological abnormalities with vitamin B12 supplements depends on the duration and severity of the symptoms and that people with chronic dementia respond poorly.
Neuropathy
A deficiency in vitamin B12 can cause nerve degeneration, which leads to a condition called neuropathy. One of the primary functions of vitamin B12 is to serve as a cofactor, or helping molecule, in a biological reaction that produces the membranes that surround and protect your nerves. The signs of peripheral neuropathy are pain and tingling in the extremities, lack of coordination, sensory loss and weakness.
Gastrointestinal Disorders
If you have vitamin B12 deficiency, you may experience a loss of appetite and nonlocalized abdominal pain. These symptoms are likely caused by an underlying gastrointestinal disorder that is causing the malabsorption of vitamin B12.
Anemia
Anemia refers to a defect in red blood cell production. The symptoms of anemia are fatigue and weakness. A review in the journal "American Family Physician" reports that more than 70 percent of people with vitamin B12 deficiency have decreases in red blood cells. The ODS reports that excessive intake of folic acid can sometimes mask the effects of vitamin B12 deficiency on red blood cell formation but it does not correct any associated neurological damage that occurs in your body.
