Synergistic Effects of Combined Resistance Exercise and Vitamin D Supplementation on Cardiometabolic Profiles and Functional Capacities in Elderly Women with Type 2 Diabetes

Background/Objectives: This 12-week randomized controlled trial investigated whether progressive resistance training combined with vitamin D supplementation produces synergistic improvements in cardiometabolic profiles and functional capacities compared with monotherapies in elderly Korean women with type 2 diabetes mellitus (T2DM) and vitamin D deficiency. Methods: In a 2×2 factorial design, 52 women (aged 65–80 years) with T2DM and serum 25(OH)D <20 ng/mL were assigned to four groups: Exercise + Vitamin D (Ex+VitD, n=15), Exercise + Placebo (Ex+Placebo, n=13), Vitamin D only (VitD, n=11), or Control (n=13). Exercise groups completed supervised progressive resistance training three times weekly, and vitamin D groups received 2,000 IU/day cholecalciferol. Results: The Ex+VitD group achieved significant improvements in HbA1c (−0.13%, p=0.019), fasting glucose (−0.79 mmol/L, p<0.001), insulin (−1.96 μU/mL, p=0.050), and HOMA-IR (−0.77, p=0.020). Serum 25(OH)D increased substantially (+15.57 ng/mL, p<0.001). Calcitonin rose exclusively in the Ex+VitD group (+2.57 pg/mL, p<0.001, d=3.34), while monotherapies showed no change. Total cholesterol (−23.93 mg/dL), triglycerides (−25.07 mg/dL), and LDL-cholesterol (−10.20 mg/dL) decreased significantly. Both exercise groups showed marked strength gains (chair stand +8.33 to +10.00 repetitions, p<0.001) and balance improvements (functional reach +2.47 to +4.46 cm, p≤0.033). Conclusions: Twelve weeks of progressive resistance training combined with vitamin D supplementation produced synergistic improvements in glycemic control, insulin sensitivity, calcitonin secretion, muscular strength, and lipid metabolism in elderly women with T2DM and vitamin D deficiency, targeting complementary pathways that neither intervention engaged alone.