Concepts and Controversies in Evaluating Vitamin K Status in Population-Based Studies.

M Kyla Shea,Sarah L Booth

doi:10.3390/nu8010008

Abstract

A better understanding of vitamin K’s role in health and disease requires the assessment of vitamin K nutritional status in population and clinical studies. This is primarily accomplished using dietary questionnaires and/or biomarkers. Because food composition databases in the US are most complete for phylloquinone (vitamin K1, the primary form in Western diets), emphasis has been on phylloquinone intakes and associations with chronic diseases. There is growing interest in menaquinone (vitamin K2) intakes for which the food composition databases need to be expanded. Phylloquinone is commonly measured in circulation, has robust quality control schemes and changes in response to phylloquinone intake. Conversely, menaquinones are generally not detected in circulation unless large quantities are consumed. The undercarboxylated fractions of three vitamin K-dependent proteins are measurable in circulation, change in response to vitamin K supplementation and are modestly correlated. Since different vitamin K dependent proteins are implicated in different diseases the appropriate vitamin K-dependent protein biomarker depends on the outcome under study. In contrast to other nutrients, there is no single biomarker that is considered a gold-standard measure of vitamin K status. Most studies have limited volume of specimens. Strategic decisions, guided by the research question, need to be made when deciding on choice of biomarkers.

Highlights

Vitamin K is a class of structurally-similar compounds, all of which function as an enzymatic co-factor in the γ-carboxylation of vitamin K-dependent proteins [1]
Despite the multiple measures available, population‐ and clinic‐based studies of vitamin K status are challenged by the lack of16a single gold‐standard measure
Food composition databases are being expanded to include multiple menaquinone forms, so dietary questionnaires will no longer be limited to phylloquinone intake

Summary

Introduction

Vitamin K is a class of structurally-similar compounds, all of which function as an enzymatic co-factor in the γ-carboxylation of vitamin K-dependent proteins [1]. K-dependent proteins are clotting proteins, vitamin K-dependent proteins are present in many extra-hepatic tissues that have been implicated in many chronic diseases [2]. Kin health and disease emerge, so has interest in measuring vitamin K status in population-based studies. The purpose of this review is to evaluate the methods currently available to assess vitamin K status in human studies. Dietary forms of vitamin K fall into two general categories: Phylloquinone (vitamin K1) and menaquinones (collectively referred to as vitamin K2), which are comprised of at least 10 compounds (menaquinone-4 to menaquinone-13) that differ from phylloquinone in the length and saturation of their side-chain (Figure 1)

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Conclusion