Objective To investigate the nutritional quality characteristics of vitamin D3-fortified yogurt and explore its improving effect on vitamin D metabolism in the body under simulated weightlessness,thereby providing a theoretical basis for the development of functional foods.Methods Using reconstituted milk as the matrix and Vitamin D3(VD3)microcapsule powder as the fortifier,VD3-fortified yogurt was prepared.A systematic study was conducted to investigate the effects of different gradients(1.25 μg/100 mL,2.50 μg/100 mL,3.75 μg/100 mL,5.00 μg/100 mL,6.25 μg/100 mL)of VD3 microcapsule addition on its quality characteristics(titratable acidity,solid content,water-holding capacity,syneresis).In vivo assessments were conducted using a Sprague-Dawley(SD)rat tail-suspension model to simulate weightlessness.Levels in serum 25(OH)D3,1,25-(OH)2D3,calcium(Ca),and phosphorus(P)were detected using the enzyme-linked immunosorbent assay(ELISA)to evaluate its metabolic capacity.Results During fermentation(3 h),titratable acidity of VD?-fortified yogurt initially increased,then decreased,and eventually stabilized with rising microcapsule dosage,while total solid content remained consistent.WHC exhibited an initial increase followed by a decline,whereas syneresis showed an inverse trend.At an optimal dosage of 3.75 μg/100 mL,the yogurt displayed a dense and uniform network structure,characterized by non-Newtonian fluid behavior with shear-thinning properties.This formulation demonstrated robust structural stability under high-frequency mechanical stress,alongside desirable textural,flavor,and sensory attributes.Animal experiments revealed that the serum concentrations of 25(OH)D3,1,25-(OH)2D3,calcium,and phosphorus in the vitamin D?-fortified yogurt intervention group were significantly higher than those in the tail-suspended control group(P<0.05).Conclusion VD? microencapsulation technology effectively preserves and enhances the nutritional quality characteristics of yogurt and mitigates vitamin D metabolic dysregulation under simulated weightlessness.