Recent trends in the metabolism and cell biology of vitamin K with special reference to vitamin K cycling and MK-4 biosynthesis

Shearer MJ, Newman P · Journal of Lipid Research

Explains why the K1-versus-K2 argument is not as clean as it is usually presented, and puts a size on it. The body does make menaquinone-4 out of dietary phylloquinone, but not by tissues converting one to the other: the side chain is cleaved in the intestine, the menadione released travels by mesenteric lymph, and tissues prenylate it locally through UBIAD1. The review calls the proportion small and quotes the cannulated-rat experiment that measured it — about 2% of absorbed labelled phylloquinone converted to menadione and about 0.1% to MK-4 — beside the finding that 1-5% of an oral dose leaves in human urine as menadione metabolites within 24 hours. Labelled MK-4 concentrated in the cerebrum and barely appeared in the liver.

Population

Vitamin K metabolism

Intervention

Not applicable

Comparator

Not applicable

Limitations

A metabolism review, and the quantities in it come from rats with cannulated lymph and blood vessels; the human figure is a urinary excretion fraction, not a tissue conversion rate. How much MK-4 a human tissue makes from a dietary dose is still not settled. Nothing in it concerns a joint.