Background: Emerging evidence suggests novel roles for bacterially derived vitamin K forms known as menaquinones in health and disease, which may be attributable in part to anti-inflammatory effects. However, the relevance of menaquinones produced by gut bacteria to vitamin K requirements and inflammation is undetermined. Objective: This study aimed to quantify fecal menaquinone concentrations and identify associations between fecal menaquinone concentrations and serum vitamin K concentrations, gut microbiota composition, and inflammation. Design: Fecal and serum menaquinone concentrations, fecal microbiota composition, and plasma and fecal cytokine concentrations were measured in 80 men and postmenopausal women (48 men, 32 women, age 40–65 y) enrolled in a randomized, parallel-arm, provided-food trial. After consuming a run-in diet for 2 wk, participants were randomly assigned to consume a whole grain–rich (WG) or a refined grain–based (RG) diet for 6 wk. Outcomes were measured at weeks 2 and 8. Results: The median total daily excretion of menaquinones in feces was 850 nmol/d but was highly variable (range: 64–5358 nmol/d). The total median (IQR) fecal concentrations of menaquinones decreased in the WG diet compared with the RG diet [26.8 nmol/g (13.0 nmol/g) dry weight for WG compared with 1.8 nmol/g (12.3 nmol/g) dry weight for RG; P, 0.01)]. However, interindividual variability in fecal menaquinone concentrations partitioned individuals into 2 distinct groups based on interindividual differences in concentrations of different menaquinone forms rather than the diet group or the time point. The relative abundances of several gut bacteria taxa, Bacteroides and Prevotella in particular, differed between these groups, and 42% of identified genera were associated with $1 menaquinone form. Menaquinones were not detected in serum, and neither fecal concentrations of individual menaquinones nor the menaquinone group was associated with any marker of inflammation. Conclusion: Menaquinone concentrations in the human gut appear highly variable and are associated with gut microbiota composition. However, the health implications remain unclear. This trial was registered at clinicaltrials.gov as NCT01902394.
Bibliographical noteFunding Information:
Supported by the Bell Institute of Health and Nutrition, General Mills, Inc. and by the USDA/ARS under agreement 58-1950-7-707. JPK was supported by the Science, Mathematics, and Research Transformation Defense Education Program. SMV was supported by Stanley N Gershoff Scholarship of the Tufts University Friedman School of Nutrition Science and Policy, by a National Research Service Award from the NIDDK T32 Research Training Program in Nutrition and Chronic Disease (grant 2T32DK062032-21), by an American Society for Nutrition 2012 Kraft Foods, Inc. predoctoral fellowship, and by the USDA/ARS (agreement 58-1950-0-014).
- Vitamin K
- Whole grain