Are Higher Vitamin D Levels Linked to Lower Hospitalization from Respiratory Infection? Study Reveals

Vitamin D is often associated with bone strength, but it also plays a key role in how the immune system fights infections. Researchers say this nutrient helps the body mount antibacterial and antiviral responses, which may reduce the severity of infections that affect the lungs. Despite this, vitamin D deficiency remains widespread, particularly in countries with limited sunlight exposure during winter months.

To explore this connection, scientists from the University of Surrey, working with researchers at the University of Reading and the University of Oxford, analyzed health data from 36,258 participants in the UK Biobank. The study focused on middle-aged and older adults—groups already at higher risk of respiratory infections. Vitamin D levels measured in blood samples were compared with NHS hospital records to track admissions for respiratory tract infections over time.

The findings were striking. Individuals with severe vitamin D deficiency—defined as blood levels below 15 nmol/L—were 33 percent more likely to be hospitalized for respiratory infections than those with sufficient levels of at least 75 nmol/L. The analysis also showed a clear dose-response relationship: for every 10 nmol/L increase in vitamin D, the risk of hospitalization dropped by around four percent. These patterns remained consistent even after accounting for factors such as age, sex, lifestyle, and existing health conditions.

Lead author Abi Bournot explained that the results provide strong real-world evidence supporting the idea that vitamin D helps protect against serious respiratory illness. Senior author Dr. Andrea Darling added that reducing hospital admissions through better vitamin D status could ease pressure on already stretched healthcare systems like the NHS.

The researchers emphasize that supplementation—particularly during winter when sunlight exposure is low—along with vitamin D–fortified foods, could be a practical public health strategy. Older adults and ethnic minority communities, who are at greater risk of deficiency, may benefit the most.

This large-scale study highlights how maintaining healthy vitamin D levels could be a simple yet powerful tool to reduce severe respiratory infections and hospitalizations.

REFERENCE: Abigail R Bournot, Kathryn H Hart, S Johnsen, D Ian Givens, Julie A Lovegrove, José M Ordóñez-Mena, Simon de Lusignan, David B Bartlett, Susan A Lanham-New, Andrea L Darling; Association between serum 25-hydroxyvitamin D status and respiratory tract infections requiring hospital admission: unmatched case-control analysis of ethnic groups from the United Kingdom Biobank cohort; The American Journal of Clinical Nutrition; 2025; https://doi.org/10.1016/j.ajcnut.2025.101179.