A systematic review on the mechanisms of vitamin K effects on the complications of diabetes and pre-diabetes.

Diabetes mellitus and pre-diabetes are prevalent endocrine disorders associated with substantial morbidity and premature mortality. Vitamin K is known to have several beneficial effects on complications of diabetes and pre-diabetes. However, systematic consolidation of evidence is required to quantify these effects in order to inform clinical practice and research. A systematic search in PubMed, Scopus, Embase, ProQuest, and Google Scholar databases was undertaken from database inception up to October 2018 to evaluate functional roles of different forms of vitamin K on diabetes and pre-diabetes. From 3,734 identified records, nine articles met the inclusion criteria and were evaluated. Vitamin K supplementation was found to be associated with significant reductions in blood glucose (six studies), increased fasting serum insulin (four studies), reduced hemoglobin A1c (three studies), reduced homeostatic model assessment-insulin resistance index (HOMA-IR) (two studies), and increased ß-cell function (two studies) in diabetic animal studies. Following 2-hour oral glucose tolerance test, vitamin K supplementation was observed to be effective in reducing blood glucose and insulin levels in the pre-diabetic population. However, no evidence of effect was observed for fasting blood sugar, insulin, HOMA-IR, and homeostatic model assessment-β-cell function index (two studies). A statistically significant effect was also noted with vitamin K in improving dyslipidemia (three studies) as well as oxidative stress and inflammatory markers (five studies) in diabetic animals. In conclusion, clinical trials and animal studies confirm that vitamin K supplementation may improve both clinical features and complications of diabetes and pre-diabetes. However, quantification of clinical efficacy in the pre-diabetic population and among individuals with comorbidities requires further investigation.