Vitamin B12 deficiency

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

B12 deficiency can potentially cause severe and irreversible damage, especially to the brain and nervous system.

The daily cobalamin (vitamin B12) requirement is 1-2 mcg. An intake of 5-20 mcg/day is usual in a Western diet. The total body can store 2-5 mg. 60% of vitamin B12 is efficiently absorbed via the ileum when it is bound to intrinsic factor (IF).

The first deficiency symptom that was discovered was anemia characterized by enlarged blood corpuscles, so-called megaloblastic anemia.

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.

Far more serious is the damage to the nervous system that may occur due to deficiency.

For vegans, the risk is very high because none of their natural food sources contain B₁₂. One American study found blood levels below normal in 92 % of vegans, 64 % of lacto-vegetarians, and 47% of lacto-ovo vegetarians.^[1] The study applied the old normal values, so in reality a considerably greater proportion may have been deficient.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Nabeel Ahmed, M.B.B.S

• Dietary Vitamin B12 binds to salivary R factor then the complex arrives at small intestine.^[1]
• In duodenum Vitamin B12 is detach from R- factor by pancreatic proteases.
• Now free B12 binds to intrinsic factor which is secreted by gastric parietal cell.
• The intrinsic factor – B12 complex is absorbed in the ileum.
• Absorbed vitamin B12 is use in metabolic pathways which is important for neurologic and hematologic function if vitamin B12 is deficit regardless of the cause many impairments may occur .
• Vitamin B12 is a cofactor for the enzyme methionine synthase which convert homocysteine to methionine as a result methyl- THF is converted to THF which is use in synthesis of pyrimidine base of DNA.
• In B 12 deficiency homocysteine accumulate which cause megaloblastic anemia and hypersegmented neutrophils.
• Vitamin B 12 is a cofactor for enzyme methylmalonyl-COA mutase , which converts methylmalonic-COA to succinyl-COA. In B 12 deficiency methylmalonic acid (MMA ) will accumulate. MMA and elevated level of homocysteine cause damage of myelin as a result subacute combined degeneration of spinal cord ( SCDSC ) occur . This affects dorsal columns, lateral corticospinal tracts and spinocerebellar tract as result loss of proprioception , ataxia , peripheral neuropathy and dementia.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Luke Rusowicz-Orazem, B.S.

Common causes of vitamin B12 deficiency include insufficient dietary intake, as well as diseases and iatrogenic procedures causing problems in absorption. It is common in individuals adhering to vegetarian or vegan diets without external supplementation, due to primary sources including animal products such as meat, eggs, and dairy.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

A large study in the US found that 39 % people had low values.^[1] This study at Tufts University used the B12 concentration 258 pmol/l (= 350 pg/liter) as a criterion of “low level”. Research has shown that B12 deficiency may occur at a much higher B12 concentration (500-600 pg/l). On this basis Mitsuyama and Kogoh ^[2] proposed 550 pg/l, and Tiggelen et al ^[3] proposed 600 pg/l. Against this background, there are reasons to believe that B12 deficiency is present in a far greater proportion of the population than 39% as reported by the Tufts University.

In the developing world the deficiency is very widespread, with significant levels of deficiency in Africa, India, and South and Central America. This is due to low intakes of animal products, particular among the poor and strict vegan Increased intake of animal products or supplements have been suggested.^[4]

B12 deficiency is even more common in the elderly.^[5] This is because B₁₂ absorption decreases greatly in the presence of atrophic gastritis, which is common in elderly.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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For vegans, the risk is very high because none of their natural food sources contain B₁₂. One American study found blood levels below normal in 92 % of vegans, 64 % of lacto-vegetarians, and 47% of lacto-ovo vegetarians.^[1] The study applied the old normal values, so in reality a considerably greater proportion may have been deficient.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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