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Vitamin B12 levels

Vitamin B12 also known as cyanocobalamin (cobalamin) is a member of the vitamin group B, essential one-carbon metabolism, in which folate transfers one-carbon groups in a range of biological processes including DNA and protein synthesis, methylation, and homocysteine metabolism. In these processes soluble B vitamins (folate, B6, and B12) act as cofactors or substrates.

Clinical B12 deficiency, with haematological or neurological manifestations, is relatively uncommon. Low or marginal B12 deficiency without haematological or neurological impairments is frequently caused by an inadequate diet, especially among children and women of reproductive age. Low B12 levels are more frequent among older adults (≥60 years of age) than young adults (19–39 years of age) and more prevalent in women than men.

The determination of methylmalonic acid (MMA), an indicator of the B12 status, and homocysteine are frequently tested in clinical practice to detect B12 deficiency (Green et al., 2017). Measurement of total serum B12 levels has the limitation of that it includes total circulating vitamin B12, of which approximately 80% is bound to haptocorrrin, and therefore, not bioavailable for cellular uptake. However, the determination of B12 levels in clinical practice is not obsolete since it can be helpful to predict the prognosis and status of several diseases that are related to high vitamin B12 levels such as cancer and autoimmune lymphoproliferative syndrome.

It has been described genetic variants that may alter vitamin B12 levels by affecting the proteins involved in absorption, cellular uptake, and intracellular metabolism. According to studies conducted in monozygotic and dizygotic twins, the heritability of vitamin B12 levels is approximately 59%.

Gene or region studied

  • FUT2
  • FUT6
  • TCN1
  • TCN2
  • MMUT
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