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B12 deficiency is a reduction in vitamin B12 from inadequate dietary intake or impaired absorption. The condition is commonly asymptomatic, but can also present as anemia characterized by enlarged blood corpuscles, so-called megaloblastic anemia. However in serious cases deficiency can potentially cause severe and irreversible damage to the nervous system, including subacute combined degeneration of spinal cord.
The anemia is thought to be due to problems in DNA synthesis, specifically in the synthesis of thymine, which is dependent on products of the MTR reaction. Other cell lines such as white blood cells and platelets are often also low. Bone marrow examination may show megaloblastic hemopoiesis. The anemia is easy to cure with vitamin B12.
Early and even fairly pronounced deficiency does not always cause distinct or specific symptoms. Common early symptoms are tiredness or a decreased mental work capacity, decreased concentration and decreased memory, irritability and depression.
Sleep disturbances may occur, because B12 may be involved in the regulation of the sleep wake cycle by the pineal gland (through melatonin)[1].
Neurological signs of B12 deficiency, which can occur without anemia, include sensory disturbances due to damage to peripheral nerves caused by demyelination and irreversible nerve cell death. Symptoms include numbness, tingling of the extremities, disturbed coordination and, if not treated in time, an ataxic gait, a syndrome known as subacute combined degeneration of spinal cord.
B-12 deficiency can also cause symptoms of mania and psychosis.[2][3]
Recent studies have devalued a possible connection between B12 deficiency and Alzheimer’s dementia, and such a correlation is unlikely as of June 2007.[4]
Studies showing a relationship between clinical depression levels and deficient B12 blood levels in elderly people are documented in the clinical literature.[5] and 2002 [6]
Bipolar disorder appears to genetically co-segregate with the hereditary B12-deficiency disorder pernicious anemia [7][8].
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