Vitamin K Kinetics

George received a series of questions about vitamin K kinetics from colleague and friend Catherine N. Otto, MLS, PhD, Rutgers University. Dr. Otto is assisting a Nutrition Science colleague.

• It seems that vitamin K deficiency (as defined by PT/INR) does not show up until there is serious depletion in the amounts of these activated proteins. Why?
• Do the activated clotting proteins have a longer half-life than vitamin K? They seem to sustain in times of frank vitamin K deficiency.
• What is the minimum level of vitamin K at which we see a prolonged PT?

We found no references that answer these questions, and only one reference that measure vitamin K kinetics: Novotny JA, Kurilich AC, Britz SJ, Baer DJ, Clevidence BA. Vitamin K absorption and kinetics in human subjects after consumption of 13C-labelled phylloquinone from kale. Br J Nutr. 2010;104:858–62.

We’d appreciate the help of our participants in this question.