Background: Vitamin D plays a crucial role in numerous physiological systems, including the muscular, immune, and endocrine systems, as well as calcium and bone homeostasis. Vitamin D deficiency, a global health problem affecting billions of people, is associated with adverse health outcomes and can serve as a marker for health status, disease severity, and length of hospital stay (LOS). Nutritional supplementation has been shown to be highly beneficial and is strongly recommended. Methods: In this study, the medical records of 834 hospitalized patients were retrospectively analyzed, with a focus on 25-hydroxyvitamin D [25(OH)D] levels. The patients were divided into groups based on serum vitamin D levels: deficient, suboptimal, adequate, and high. Correlations between vitamin D levels, LOS, laboratory parameters, comorbidities, seasonal variations, medical diagnosis of deficiency, and supplementation were examined. Results: Vitamin D deficiency was common and associated with a longer LOS. Women had higher vitamin D levels than men. No seasonal variation was observed. Only 14% of the patients took supplements before hospitalization, and 61% of the patients with vitamin D deficiency received supplementation. Conclusions: Routine vitamin D screening, tailored supplementation, and increased public awareness are essential to reduce hospitalizations, improve treatment outcomes, and promote independence among at-risk groups.