The Differential Effects of Vitamin K Across Glycaemic Outcomes in Prediabetes and Type 2 Diabetes Mellitus

<b>Background:</b> Vitamin K has emerged as a promising regulator of glucose metabolism in preclinical studies. There is, however, scant evidence to support this promising potential in a clinical setting. <b>Aim:</b> The aim of this study was to confirm the effects of vitamin K supplementation on glycaemic parameters such as fasting blood glucose (FBG), fasting insulin (FI), glycated haemoglobin (HbA1c), insulin resistance (HOMA-IR), and homeostatic model of beta cell function (HOMA-β) across randomised controlled trials (RCTs). <b>Materials and Methods</b>: This meta-analysis used evidence from PubMed, Scopus, and manual screening. Only RCTs were considered for this meta-analysis of interventional studies. The Meta online tool was used to analyse data, with the results reported as either the mean or the standardised mean difference (SMD), alongside 95% confidence intervals (CI). <b>Results:</b> Only eight RCTs were found relevant and analysed; the age of those in the vitamin K group was 50.58 ± 6.91 years, and in the control group, it was 48.19 ± 5.41. The evidence showed a significant reduction in FBG, SMD = -0.22 (-0.39 to -0.05), HbA1c, MD = -1.00%, 95% CI (-1.92 to -0.07), and HOMA-IR, MD = -0.63, 95% CI (-1.20 to -0.06). However, no effect was observed on insulin (SMD = -0.39, 95% CI: -0.91 to 0.13, <i>p</i> = 0.15) and HOMA-β (MD = 6.56, 95% CI (-3.89 to 17.01), <i>p</i> = 0.2184. Low doses of vitamin K2 and vitamin K1 were associated with reduced HbA1c and HOMA-IR, respectively. An intervention of less than 12 weeks was associated with reduced HOMA-IR. <b>Conclusions:</b> This study showed a significant decrease in FBG, HbA1c, and HOMA-IR without affecting insulin or HOMA-β. Nevertheless, the limited number of trials with moderate quality warrants larger, longer-term RCTs with rigorous methodology and direct comparisons of vitamin K isoforms to better assess therapeutic potential.