Strongest evidence. The most robust findings are for pain reduction, where 6 of 8 studies (moderate evidence) show small to moderate benefits, particularly in postoperative settings such as dental surgery and joint replacement. Lowering systolic blood pressure shows consistent benefit across 4 studies (moderate evidence), with effects noted in adults with diabetes and heat-exposed workers, though only one study specified a dose of 130 mg/day. Reducing interleukin-6 levels is supported by 4 of 7 studies (moderate evidence), with doses of 250–1000 mg/day, primarily in acute clinical settings like cardiac surgery and sepsis.
Mixed or weaker evidence. For oxidative stress, 3 of 4 studies (moderate evidence) show benefit, but effects vary widely by population. Tumor necrosis factor-alpha reduction is supported by only 2 of 5 studies (low evidence), with benefit limited to septic shock patients. Lung function improvement (2 of 4 studies beneficial), diastolic blood pressure reduction (2 of 3 studies), and cognitive function (1 of 3 studies) all carry low evidence due to small sample sizes and inconsistent results. Mortality risk reduction shows one beneficial meta-analysis, but two large RCTs found harm from high-dose vitamin C in sepsis and COVID-19 (low evidence). Uric acid reduction, hospital stay length, and gingival index show predominantly neutral or preliminary findings.
Effective dose patterns. Across outcomes with moderate evidence, effective doses cluster between 250 and 1000 mg/day, though many studies did not report specific doses. The pain reduction studies had a median duration of 60 days, while interleukin-6 studies ranged from acute (1 day) to longer-term (84 days). Blood pressure studies suggest effects may appear after about 40 days of supplementation.
Population insights. Benefits are most consistently seen in clinical populations—postoperative patients, individuals with sepsis, type 2 diabetes, or cardiac conditions. Generalizability to healthy populations is uncertain for many outcomes, as studies in athletes or young healthy adults often show neutral results. Deficient populations were not specifically studied in these syntheses.
Notable caveats. Publication bias is a concern for multiple outcomes, as null results may be underreported. Many studies used vitamin C in combination with other agents (thiamine, vitamin E), making it difficult to isolate its effect. High-dose vitamin C (intravenous) in sepsis and COVID-19 has shown potential harm in two large RCTs, underscoring context-dependent safety. Evidence bases are small (3–8 studies per outcome), and dose reporting is inconsistent.