Vitamin D Deficiency Is Associated with Greater Sarcopenia-Related Risk Severity and Functional Decline in Older Adults: A Retrospective Cross-Sectional Study

Background and Objectives: Vitamin D deficiency has been implicated in muscle weakness and functional decline among older adults. However, its association with sarcopenia-related impairment, particularly when evaluated using readily available nutritional and functional indicators in routine clinical practice, remains incompletely understood. Materials and Methods: This retrospective cross-sectional study included 148 adults aged ≥65 years who attended a Physical Medicine and Rehabilitation outpatient clinic. Sarcopenia-related risk was classified using an EWGSOP2-informed operational framework based on handgrip strength together with nutritional and functional indicators available in the retrospective dataset. Serum 25-hydroxyvitamin D [25(OH)D] concentrations were measured using a chemiluminescent microparticle immunoassay. Group comparisons, correlation analyses, and multivariable logistic regression analyses were performed. Results: The prevalence of probable sarcopenia and probable sarcopenia with nutritional/functional risk indicators was significantly higher among participants with vitamin D deficiency. Serum 25(OH)D levels differed significantly across the three study groups (p < 0.001). Post-hoc Tukey analysis demonstrated significantly lower serum 25(OH)D concentrations in the probable sarcopenia with nutritional/functional risk indicators group than in both the no sarcopenia and probable sarcopenia groups (both p < 0.001). Serum 25(OH)D levels were moderately and inversely correlated with sarcopenia-related risk severity (r = −0.48, p < 0.001). Lower vitamin D levels were also associated with reduced serum albumin levels and a higher prevalence of falls and assistive walking device use. In multivariable logistic regression analysis, vitamin D deficiency remained independently associated with sarcopenia-related risk after adjustment for age and sex. Conclusions: Vitamin D deficiency was significantly associated with greater sarcopenia-related risk severity and poorer functional status in older adults. Assessment of vitamin D status may therefore represent a simple, inexpensive, and readily available tool for identifying individuals at increased risk of sarcopenia-related impairment in routine geriatric practice. Prospective studies incorporating direct measures of muscle quantity and standardized physical performance assessments are needed to confirm these findings.