In critically ill patients with COVID-19 pneumonia and acute respiratory failure, high-dose intravenous vitamin C (6 g/day for 96 hours) was not associated with a statistically significant reduction in 28-day mortality or median ICU stay, despite improvements in biomarkers including SOFA score, CRP, and ferritin.

High doses of vitamin C lower inflammation in the lungs and blood by soaking up harmful molecules and turning off a key inflammation switch, which reduces swelling and organ stress. It also helps the body make more of a natural chemical that tightens blood vessels, reducing the need for strong drugs to maintain blood pressure. These changes improve lab markers of illness, but they do not lead to fewer deaths or shorter hospital stays because the underlying damage from the virus is too severe to reverse with this intervention alone.