Strongest evidence: Outcomes with moderate evidence strength include Reduced Pain (6 of 8 studies beneficial, small effect size), Reduced Interleukin-6 Levels (4 of 7 studies beneficial, small effect, effective dose 250–1000 mg/day), Reduced Systolic Blood Pressure (4 of 4 studies beneficial, moderate effect, dose ~130 mg/day in one study), and Reduced Oxidative Stress (3 of 4 studies beneficial, mixed effect, dose 1000 mg/day). These findings are supported by multiple studies but are limited by small sample sizes and potential publication bias.
Mixed or weaker evidence: Low evidence strength outcomes show inconsistent or null results. For example, Reduced Mortality Risk (only 1 of 7 studies beneficial, 1 harmful), Reduced Tumor Necrosis Factor Alpha (2 of 5 beneficial, dose 250–1000 mg/day), Improved Lung Function (2 of 4 beneficial, dose 500 mg/day in one positive RCT), and Reduced Diastolic Blood Pressure (2 of 3 beneficial, mixed effect sizes). Other low-evidence outcomes (Cognitive Function, Uric Acid, Hospital Stay, Gingival Index) are predominantly neutral or have only a small minority of beneficial studies.
Effective dose patterns: When doses were specified, they typically fell between 250 mg and 1000 mg per day. The 1000 mg/day dose was common in studies on oxidative stress and interleukin-6, while lower doses (130–250 mg/day) appeared in blood pressure trials. However, many studies did not report doses, and no consistent dose–response relationship emerged across outcomes.
Population insights: The vast majority of evidence comes from clinical populations: surgical patients (pain), cardiac surgery and septic shock patients (interleukin-6, mortality), individuals with type 2 diabetes (blood pressure), and older adults with sarcopenia (oxidative stress). Very few studies included healthy general populations, limiting the direct applicability of these findings to supplement users without specific health conditions.
Notable caveats: Publication bias is a recurring concern, especially for pain and blood pressure outcomes, where null results may be underreported. Many individual studies did not reach statistical significance, and the evidence base for most outcomes is small (3–8 studies). Dose and duration reporting is inconsistent, and several studies combined vitamin C with other interventions, making it difficult to isolate its specific effect.