Association between vitamin D supplementation and mortality in elderly critically ill patients: a retrospective propensity score–matched cohort study

Purpose Vitamin D deficiency is highly prevalent among elderly critically ill patients and has been associated with adverse outcomes. However, evidence regarding the prognostic benefit of vitamin D supplementation in this population remains limited. This study aimed to investigate the association between vitamin D supplementation and 28-day mortality in elderly patients admitted to the intensive care unit (ICU). Methods This retrospective cohort study utilized data from the medical information mart for intensive care IV (MIMIC-IV) database, including patients aged ≥65 years. Propensity score matching (PSM) balanced baseline characteristics between patients who received vitamin D within 48 h of ICU admission and those who did not. Cox proportional hazards models estimated hazard ratios (HRs) with 95% confidence intervals (CIs), and E-value analysis assessed unmeasured confounding. Results After PSM, 8,111 patients were included, with 1,338 (16.5%) deaths within 28 days. The 28-day mortality rate was significantly lower in the vitamin D supplementation group than in the non-supplemented group (14.5% vs. 17.0%, P = 0.017). Multivariable Cox regression demonstrated that vitamin D supplementation was independently associated with lower 28-day mortality (HR = 0.819, 95% CI: 0.710–0.946, P = 0.006). Subgroup analyses revealed more pronounced associations in females and patients without certain chronic comorbidities. Conclusion Vitamin D supplementation within 48 h of ICU admission was significantly associated with reduced 28-day mortality in elderly critically ill patients. Further prospective interventional studies are required to verify causal relationships and optimize administration regimens.