The Effect of Vitamin D Supplementation on Functional Outcomes in Patients Undergoing Rehabilitation After an Ischemic Stroke: A Prospective, Single-Blind, Randomized, Placebo-Controlled Study

<b>Background/Objectives</b>: A vitamin D deficiency is prevalent in post-stroke patients and may impair neurological recovery. While observational studies highlight the neuroprotective role of vitamin D, there is limited evidence from interventional studies evaluating its impact on functional recovery during stroke rehabilitation. This study aimed to assess whether daily vitamin D3 supplementation enhances functional recovery. <b>Methods</b>: This prospective, randomized, placebo-controlled, single-blind study included 159 patients (mean age: 62.5 ± 8.4 years) with a first ischemic stroke that were admitted for early rehabilitation. The participants were randomly allocated to receive 2000 IU of vitamin D3 daily (<i>n</i> = 79) or a placebo (<i>n</i> = 80) for six weeks. The functional outcomes were measured using the Barthel index (BI) and modified Rankin scale (mRS) at baseline and after 42 days. The serum 25-hydroxyvitamin D [25(OH)D] and insulin-like growth factor 1 (IGF-1) levels were analyzed. <b>Results</b>: Vitamin D3 supplementation significantly increased the serum 25(OH)D levels (<i>p</i> < 0.001). Supplementation was associated with improved BI scores (β = 0.07, <i>p</i> = 0.006). A higher BMI (β = -0.06, <i>p</i> = 0.033), higher NIHSS scores (β = -0.18, <i>p</i> = 0.036), hypertension, and statin use negatively impacted functional recovery. Anticoagulant use was correlated with higher mRS scores, indicating greater disability (<i>p</i> = 0.04). <b>Conclusions</b>: Vitamin D3 supplementation positively influences the functional outcomes during post-stroke rehabilitation, supporting its potential role in enhancing neuroplasticity and recovery. Larger multi-center trials are needed to confirm these findings and optimize vitamin D supplementation strategies.