Impact of vitamin D and high-protein diet on muscle quality and daily living activities in elderly diabetic patients with sarcopenia

The individual benefits of vitamin D and protein supplementation in type 2 diabetes mellitus (T2DM) and sarcopenia (SP) are recognized, yet their combined effects in elderly Chinese with different bone mass remain unclear. This study evaluated a three-month intervention of vitamin D (700–1000 IU/day) plus a high-protein diet in 100 elderly patients with T2DM and SP, stratified by bone mass status: normal ( n = 21), reduction ( n = 45), and osteoporosis ( n = 34). Post-intervention, participants showed significant improvements in appendicular skeletal muscle, skeletal muscle index, handgrip strength, short physical performance battery, bone mineral density, serum 25-hydroxyvitamin D3, osteocalcin, and modified Barthel Index. Reductions were observed in procollagen type I amino-terminal peptide, β C-terminal telopeptide of type 1 collagen, fasting glucose, and HbA1c. These findings indicate that combined vitamin D and protein supplementation may enhance musculoskeletal health, metabolic control, and functional independence in elderly patients with T2DM and SP, especially those with low bone mass. • Vitamin D plus protein improves outcomes in elderly with T2DM and sarcopenia, independent of bone mass level. • The intervention raises 25-(OH)D3, improves glycemic control, supports bone metabolism, increases BMD and muscle mass, and daily function. • Greatest benefits were seen in osteoporosis patients, suggesting higher responsiveness in those with low bone mass and reduced function.