Strongest evidence
The most robust findings are for two outcomes with moderate evidence strength. For reducing interleukin-6 levels, 3 of 5 studies reported beneficial moderate-to-large effects, with a typical dose around 1000 mg/day and effects observed over a median of 42 days in clinical populations (cardiac surgery, septic shock, hemodialysis, sarcopenia). For reducing complex regional pain syndrome (CRPS) after knee surgery, all 3 studies found small but consistent beneficial effects at 1 g daily for about 40 days (moderate evidence, though limited to surgical patients).
Mixed or weaker evidence
Six outcomes have low-strength evidence, meaning conclusions are preliminary. Reduced systolic blood pressure (3 of 3 studies beneficial, moderate effect ~3.7 mmHg) and reduced oxidative stress (3 of 4 studies beneficial) both show favorable directions but come from small study bases. Reduced pain (3 of 4 studies beneficial, moderate effect) and reduced tumor necrosis factor alpha (2 of 4 studies beneficial, moderate effect) are promising but inconsistent or limited by study quality. Improved lung function (2 of 3 studies beneficial, moderate effect) and reduced mortality risk (only 1 of 5 studies beneficial) remain uncertain. Reduced length of hospital stay showed no benefit in any of 3 studies (all neutral).
Effective dose patterns
Studies reporting effective doses frequently converged on 1000 mg/day, seen for interleukin-6 reduction, CRPS prevention, and oxidative stress. For TNF-α reduction, the effective range was 250–1000 mg/day. Doses were not consistently reported for blood pressure, pain, or mortality outcomes.
Population insights
Nearly all evidence comes from clinical or surgical populations (e.g., septic shock, cardiac surgery, knee arthroplasty, COVID-19, diabetes). Benefit in generally healthy adults is largely unstudied for these endpoints. For CRPS, benefit was demonstrated specifically in patients undergoing total knee arthroplasty, and for interleukin-6, effects were seen in various ill populations.
Notable caveats
- Publication bias is a concern for several outcomes — null studies may be underrepresented.
- Many studies used vitamin C as part of combination therapy (with thiamine, vitamin E, corticosteroids, etc.), making it difficult to isolate vitamin C’s specific effect.
- Sample sizes were often small; the evidence base for each outcome ranged from 3 to 5 studies only.
- Effects for mortality and hospital stay were studied in acute critical illness over very short durations (e.g., ~4 days), limiting generalizability.