Is vitamin K consumption associated with cardio-metabolic disorders? A systematic review.

Associations have been found between various micronutrients and cardio-metabolic outcomes. Vitamin K deficiency has been associated with increased calcification of the main arteries and with insulin resistance. The present study aimed to examine the association between vitamin K intake and cardio-metabolic outcomes including cardiovascular disease, type 2 diabetes and the metabolic syndrome. A systematic review of the literature was performed in January 2010. Nine electronic databases, and trial registers, reference lists of retrieved articles and citations were searched. Intervention, cohort, case-control or cross-sectional studies in adults were included if they examined the association between vitamin K levels (dietary intake, biomarkers, supplements) on clinical outcomes relevant to cardio-metabolic disease. Five studies met the inclusion criteria (1 trial, 4 cohort studies). Heterogeneity of designs, exposures/interventions and outcomes meant that meta-analysis was not possible. No associations were found between vitamin K1 intake and coronary heart disease (CHD) (4 cohorts) or stroke (2 cohorts) in multivariate analyses. No differences were seen in the prevalence of diabetes in a trial of vitamin K1 supplementation. Two cohorts examined the effects of vitamin K2 intake on the incidence of CHD; both found significant associations where higher vitamin K2 intake was associated with fewer CHD events. Few studies have examined the effects of vitamin K intake on clinical outcomes relevant to cardio-metabolic disorders. None of the studies used biomarkers. Currently there is no evidence for an effect of vitamin K1, but results for vitamin K2 look promising. Further prospective studies are required to confirm these findings.