Vitamin B12 Transport

Your result, the one DNA position behind it, and what the research says.

6/10 confidence.

About Vitamin B12 Transport

Total vitamin B12 in blood is a poor measure of how much your cells can actually use. Only the fraction bound to transcobalamin is delivered into tissue, and that fraction is called active B12. This variant changes one building block of transcobalamin itself, and the measured difference is in how much B12 ends up bound and delivered rather than in how tightly a single molecule holds it. Two people with the same total B12 reading can therefore differ in how much reaches their cells, which is why active B12 is increasingly measured separately.

Good to know: Only the transcobalamin-bound fraction of B12 reaches your cells. A normal total B12 reading can sit alongside lower active B12. B12 comes almost entirely from animal foods, so intake sets the ceiling.

Fun fact: Vitamin B12 is the largest and most structurally complex vitamin, and it is the only one built around a metal atom, cobalt.

Discovery: The transcobalamin variant was described in the 1990s, and its effect on active B12 was measured in the early 2000s.

The Variant

The single variant behind this trait

Gene: TCN2

Variant (rsID): rs1801198

Location: Chr 22:30,615,623

dbSNP rs1801198

The studies

Transcobalamin II 775G>C polymorphism and indices of vitamin B12 status in healthy older adults (Miller JW et al., Blood, 2002)

The transcobalamin codon 259 polymorphism should be designated 776C>G, not 775G>C (Zetterberg H et al., Blood, 2003)

Other lifestyle traits

Folate Processing: A variant in the control region of the enzyme that converts synthetic folic acid into the active folate your cells use.

Vitamin B6 Levels: A variant that sets how quickly your body clears vitamin B6 from the blood, and so how much of it circulates at any given intake.

Long-Chain Fat Burning: A change in one of the fat-burning enzymes inside mitochondria, linked to the level of a particular part-processed fat that shows up in blood.

Back to All Traits

Content updated September 2026.

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