EXPRESS: Vitamin D variability might be linked to sarcopenia, especially with decreased muscle mass in older patients: a retrospective longitudinal study

Objective: The purpose of the study was to assess the relationship between variations in vitamin D levels, sarcopenia, and the fat-free mass index (FFMI) in individuals 65 years of age and above. Materials and Methods: This retrospective study included 215 individuals aged ≥65 years who were followed at a geriatric outpatient clinic between January 2024 and September 2025 and had at least two serial vitamin D measurements. Demographic characteristics, Dual X-ray Absorptiometry (DXA) based body composition, comprehensive geriatric assessment findings, comorbidities, and longitudinal vitamin D levels were recorded. Vitamin D variability was assessed using the standard deviation (SD) and coefficient of variation (CV) of repeated measurements, and its association with sarcopenia and low FFMI was evaluated using crude and adjusted logistic regression analyses. Results: The median age was found to be 78 years. Additionally, sarcopenia (140/215, 65.1%) and sarcopenic obesity (89/215, 41.4%) were observed in the participants. Patients had a median of three vitamin D measurements (range: 2–4), with a most recent median level of 24.5 ng/mL. In crude analyses, higher vitamin D variability (SD) was associated with sarcopenia (OR: 1.051, 95% CI: 1.002–1.102, p = 0.042) and lower FFMI (OR: 1.061, 95% CI: 1.004–1.121, p = 0.037), and the association with sarcopenia remained significant after adjustment (OR: 1.057, 95% CI: 1.001–1.117, p = 0.048). Among participants with CFS <5 and a vitamin D measurement obtained within the past two years (n=27), increases in SD and CV were associated with sarcopenia and low FFMI in both crude and adjusted models (all p < 0.05). However, these subgroup associations did not remain statistically significant after correction for multiple comparisons. Conclusion: In this retrospective cohort, higher vitamin D variability was associated with sarcopenia and low FFMI. As a result, it appears more important to monitor vitamin D measurements in a certain period rather than one time in the evaluation of sarcopenia. For older persons to maintain muscular health, maintaining vitamin D stability may be therapeutically significant.