Vitamin K status in healthy volunteers
E. Theuwissen Food Funct. First published online 18 Nov 2013
Vitamin K's recommended dietary allowance (RDA) is based on the hepatic requirement for clotting factor synthesis, but substantial concentrations of undercarboxylated extra-hepatic Gla-proteins are found in the circulation of non-supplemented individuals. This suggests that vitamin K intake above the RDA is required for an optimal extra-hepatic vitamin K status. Circulating uncarboxylated osteocalcin (ucOC) and desphospho-uncarboxylated matrix Gla-protein (dp-ucMGP) are considered markers of the vitamin K status in bone and the vasculature, respectively. We measured these markers in 896 samples of healthy volunteers and defined target groups for vitamin K supplementation based on increased levels indicative of tissue-specific vitamin K deficiency.
We studied the response to vitamin K supplements at different states of vitamin K deficiency by measuring the circulating dp-ucMGP level in samples from two short-term trials on menaquinone-7 (MK-7, vitamin K2) supplementation in 42 children and 68 adults. Children had high ucOC levels (3.4–96.9 ng ml−1); other age groups had values in the range of 1.5–5.0 ng ml−1.
From the age of 40 years, dp-ucMGP levels gradually increased. Children and adults with more pronounced vitamin K deficiency gave the highest responses to MK-7 supplementation. Children and adults above 40 years showed the largest tissue-specific vitamin deficiency and accordingly may benefit from MK-7 supplementation to improve their extra-hepatic vitamin K status.
