Synergistic Enhancement of Vitamin D3 and Vitamin K1 Bioavailability via Medium- and Long-Chain Triglycerides: Micelle-Mediated Absorption, Gut Microbiota and Bone Density

Vitamin D (VitD) and vitamin K (VitK), essential fat-soluble micronutrients regulating bone homeostasis and gut microbiota, exhibit high global deficiency rates. Infant formulas demonstrate low bioavailability of VitD3 and VitK1. This study investigated how medium- and long-chain triacylglycerols (MLCTs, MLCT1 vs MLCT2) with distinct MLCT concentrations (25% vs 40%) affect VitD3/VitK1 bioavailability using integrated in vitro-in vivo models. In vitro digestion revealed that 40% MLCT2 significantly enhanced free fatty acid release (52.81%, P < 0.05) and bioaccessibility (VitD3: 54.37%; VitK1: 67.14%, P < 0.05) compared to MLCT1. Pharmacokinetic analysis demonstrated that 40% MLCT2 achieved superior bioavailability (AUC: VitD3 3880.26 μg/L×h; VitK1 710.12 μg/L×h) and metabolic efficacy (serum 25OHVitD3: (34.72 ± 10.85) ng/mL; VitK1: (27.28 ± 2.5) ng/mL) compared to 25% MLCT2. Long-term animal studies showed 40% MLCT2 administration significantly improved bone mineral density ((0.10±0.02) g/cm³, P < 0.001) and enriched Bacteroidetes and Eubacterium_coprostanoligenes_group - taxa linked to vitamin metabolism. These findings establish MLCTs as advanced lipid carriers to combat VitD/VitK deficiencies, offering transformative strategies for nutrient delivery systems with enhanced bioavailability.