Rotator cuff tears are a significant health concern that severely affect shoulder joint mobility in patients. Common clinical manifestations of RCTs include shoulder pain, limited range of motion, joint instability, muscle weakness, and functional disability. In patients with rotator cuff tears, the prevalence of vitamin D deficiency ranges from 8.3% to 71%. Given its critical role in muscle strength and function, vitamin D is emerging as an important factor in the management of musculoskeletal disorders, including rotator cuff injuries. Despite the promising evidence regarding vitamin D's role in muscle strength and tendon healing, the specific impact of vitamin D supplementation on postoperative rehabilitation remains unclear. Given that vitamin D deficiency is easily diagnosed and treated, it is considered a modifiable risk factor that could be utilized in orthopedic care to improve patient outcomes. Vitamin D supplementation is a cost-effective and potentially efficient intervention that may enhance muscle strength, reduce postoperative pain, and improve joint function in patients recovering from rotator cuff repair. The objective of this study is to investigate the effects of vitamin D supplementation on postoperative outcomes in patients undergoing arthroscopic rotator cuff repair. The study will be conducted as a randomized controlled trial, with participants receiving either a daily dose of 4000 IU of vitamin D or a placebo. The primary outcomes to be evaluated include muscle strength, postoperative pain, and joint function. Blood samples will be collected at baseline, and after 3 months, 6 months, and 12 months of supplementation to monitor the effects of vitamin D on serum levels and its correlation with clinical outcomes.