Prevalence and clinical impact of vitamin C deficiency in patients hospitalized with community-acquired pneumonia

Community-acquired pneumonia (CAP) is a major global health challenge and the fourth leading cause of death worldwide, accounting for approximately 2.6 million deaths in 2019 alone . The burden of disease is particularly severe in older adults and individuals with multiple chronic conditions, who often experience poorer outcomes and increased complications during hospitalization. Despite the availability of antibiotics, advances in respiratory support, and broader public health measures, mortality associated with CAP remains unacceptably high. In an Australian multicentre study of 7853 adult patients hospitalized with CAP (excluding those with COVID-19), the in-hospital mortality rate was reported at 7.8%, with 30-day mortality rising to 16.9%. Among those requiring intensive care unit (ICU) admission, mortality increased further to 17.6%.

The pathogenesis of CAP-related morbidity and mortality is driven not only by microbial infection but also by dysregulated host immune responses, particularly inflammation and oxidative stress. During the innate immune response, activated neutrophils generate reactive oxygen species (ROS) as part of the respiratory burst during pathogen clearance. While essential for host defense, excessive ROS production can damage pulmonary tissues, contribute to acute respiratory distress syndrome (ARDS), and precipitate multi-organ failure in severe cases.

Vitamin C (ascorbic acid) is a water-soluble antioxidant and an essential micronutrient for humans, who lack the ability to synthesize it endogenously. It plays a critical role in scavenging ROS, supporting immune function, and maintaining epithelial barrier integrity. Observational studies have shown that vitamin C deficiency is prevalent among hospitalized patients, especially those with critical illness, and is associated with adverse clinical outcomes including sepsis, organ dysfunction, and increased mortality. Despite this, there remains limited evidence on the prevalence of vitamin C deficiency specifically among patients hospitalized with CAP, and even fewer studies have examined its potential impact on clinical outcomes in this population. To address this gap, we conducted a retrospective cohort study of consecutive hospitalized adult patients with CAP at two tertiary centres in South Australia. We aimed to describe the prevalence of vitamin C deficiency in this population and evaluate its association with key clinical outcomes, including hospital and ICU length of stay, mortality, and readmission.