Association Between Multivitamin Use on Admission and Clinical Outcomes in Patients Hospitalised with Community-Acquired Pneumonia: A Case—Cohort Study

Background/Objectives: Community-acquired pneumonia (CAP) is a leading cause of hospitalisations worldwide. Micronutrient deficiencies may influence CAP risk and severity, but their impact on CAP outcomes remains unclear. This study investigated the influence of multivitamin use on hospital length of stay (LOS), intensive care unit (ICU) admission, in-hospital mortality, and 30-day readmissions in hospitalised CAP patients. Methods: This retrospective cohort study included all CAP admissions, identified using ICD-10-AM codes, at two tertiary hospitals in Australia between 2018 and 2023. Pneumonia severity was determined using the CURB65 score, while frailty and nutritional status were assessed using the Hospital Frailty Risk Score (HFRS) and the Malnutrition Universal Screening Tool (MUST). Multivitamin use at admission was identified through the hospital pharmacy database. Propensity score matching (PSM) controlled for 22 confounders and the average treatment effect on the treated (ATET) was determined to evaluate clinical outcomes. Results: The mean (SD) age of the 8162 CAP cases was 75.3 (17.5) years, with 54.7% males. The mean (SD) CURB65 score was 1.9 (1.0), with 29.2% having severe CAP (CURB65 ≥ 3). On admission, 563 patients (6.9%) were on multivitamin supplements. Multivitamin users were younger, had more comorbidities, higher frailty, and higher socioeconomic status than non-users (p < 0.05). The ATET analysis found no significant differences in LOS (aOR 0.14, 95% CI 0.03–5.98, p = 0.307), in-hospital mortality (aOR 1.04, 95% CI 0.97–1.11, p = 0.239), or other outcomes. Conclusions: Multivitamin use was documented in 6.9% of CAP patients and was associated with multimorbidity and frailty but not with improved clinical outcomes. Further research is needed to determine if specific vitamin supplements may offer benefits in this population.