How long does b12 stay in the body
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Summary
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These studies suggest that vitamin B12 stays in the body for varying durations, with a half-life of about 5.14 days in plasma and up to 12 months in the liver.
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Duration of Vitamin B12 Retention in the Body
Biological Half-life of Vitamin B12 in Plasma
The biological half-life of vitamin B12 in plasma is approximately 6 days. This conclusion is drawn from kinetic analyses of isotope experiments using tracer doses of radioactive vitamin B12. These studies have shown a consistent half-life of around 5.14 days, with a velocity constant (k) of 0.1347 days⁻¹. This short half-life in plasma contrasts sharply with the much longer retention in the liver, which averages about 12 months.
Whole Body Retention of Vitamin B12
Whole body retention studies of vitamin B12 indicate that significant retention can be observed up to 14 days post-administration. In elderly subjects, retention of vitamin B12 at 14 days did not show a decline with age, suggesting that absorption efficiency remains consistent across different age groups. This finding is supported by other studies that have measured whole-body retention using various methods, confirming that vitamin B12 can be retained in the body for extended periods .
Plasma Turnover and Binding Proteins
Vitamin B12 binds to two main plasma proteins: transcobalamin I and transcobalamin II. The plasma turnover of vitamin B12 varies depending on which transcobalamin it is bound to. When bound to transcobalamin I, the half-life is approximately 9-10 days, whereas when bound to transcobalamin II, the half-life is significantly shorter at about 1.5 hours. However, the overall plasma curves for both binding proteins yield similar final slopes, indicating a half-life of around 9.3 to 9.8 days due to the rapid reappearance of the radiocobalt label bound to transcobalamin I.
Conclusion
In summary, vitamin B12 has a biological half-life in plasma of about 6 days, with whole-body retention observable for up to 14 days. The retention and turnover rates can vary based on the binding proteins involved, but overall, vitamin B12 can remain in the body for extended periods, particularly in the liver where it can be stored for up to 12 months. These findings highlight the body's ability to retain and utilize vitamin B12 efficiently over time.
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