Dietary Vitamin K Intake and Insulin Resistance Markers in U.S. Adults: NHANES 2001-2018

Background: Vitamin K (VK) has emerging roles beyond coagulation, including potential involvement in glucose metabolism. While large cohorts report inverse associations between VK status and incident type 2 diabetes, less is known about its relationship with insulin resistance markers in general populations. Methods: We conducted a cross-sectional analysis of 23,247 adults from the National Health and Nutrition Examination Survey (NHANES) 2001-2018. Dietary VK intake was assessed using a single 24 h recall and modeled as energy-adjusted nutrient density (µg/1000 kcal). Fasting insulin, homeostasis model assessment of insulin resistance (HOMA-IR), fasting glucose, and HbA1c were analyzed using survey-weighted linear regression; models were adjusted for demographic, socioeconomic, lifestyle, and adiposity-related factors. Effect modification by baseline metabolic status was evaluated, and sensitivity analyses assessed robustness. Results: Higher energy-adjusted VK intake was modestly associated with lower fasting insulin and HOMA-IR, but not with fasting glucose or HbA1c in primary linear models. Each SD increase in VK intake was associated with 1.4% lower fasting insulin (95% CI: -2.4% to -0.4%) and 1.3% lower HOMA-IR (95% CI: -2.3% to -0.3%) in fully adjusted models. Associations were attenuated following adjustment for adiposity. Effect modification by baseline metabolic status was observed, with stronger associations among normoglycemic individuals. Findings were consistent across sensitivity analyses, although effect sizes were small. Conclusions: In this nationally representative sample of U.S. adults, higher VK intake was modestly associated with lower insulin resistance markers. Prospective studies incorporating objective VK biomarkers and dynamic measures of insulin sensitivity are needed to clarify these associations.