Verdict No. 3018 · Search date 2026-09-07 · Methodology v1.0
Single-ingredient oral vitamin C,
does it really help with Brachial flow-mediated dilation in cardiovascular-risk adults?
30-Second Summary
C
Evidence Grade C · 50 · Safety caution
Do not borrow the blood-pressure or glycaemic grade.
High oral doses can cause gastrointestinal effects. Trial-specific adverse-event counts remain limited.
What the
research showsGrade C with 50 points. FMD improved in coronary-disease trials, but sustained treatment was null in some diabetes and smoking studies. FMD is not proof of preventing myocardial infarction or stroke.
research showsGrade C with 50 points. FMD improved in coronary-disease trials, but sustained treatment was null in some diabetes and smoking studies. FMD is not proof of preventing myocardial infarction or stroke.
What the
ads claimDescriptions such as artery cleansing or proportional heart-disease prevention go beyond these experiments.
ads claimDescriptions such as artery cleansing or proportional heart-disease prevention go beyond these experiments.
Useful facts when choosing a product
- This verdict concerns single-ingredient oral vitamin C and does not automatically include foods, combinations, or intravenous infusion.
- Trials with different doses, durations, and populations were not treated as interchangeable.
- High oral doses can cause gastrointestinal effects; caution is warranted with stone risk, kidney disease, or iron overload.
Chamgap Semantic Classification Code
Permanent code issued
S.vitamin-c.oral.flow-mediated-dilation.improve.placeboSupplements and nutraceuticals > Vitamin C > Oral > Flow-mediated dilation > Improvement claim > Placebo
Permanent semantic code issued; FMD remains identified as a surrogate rather than a clinical event. The code identifies the intervention and claim; it never contains the evidence grade, score, or safety result.
Exact Claim Classification
These independent facets prevent evidence from different forms, routes, populations, effects, and comparators from being mixed.
| Intervention class | S · Supplement or nutraceutical |
|---|---|
| Canonical ingredient or intervention | Vitamin C |
| Source or part used | Purified nutrient. Feedstock, manufacturing process and country are unverified; plant part is not applicable. |
| Formulation or processing | Single-ingredient ascorbic acid supplement; unverified tablet/capsule, salt and excipient details are flagged by study. |
| Route | Oral |
| Dose | Acute 2 g; 500 mg/day for 30 days or 1 g/day for eight weeks |
| Duration | Two-hour response separated from 30-day and eight-week exposure |
| Population | CAD, hypertension and smoking cohorts kept separate; other vascular tests in diabetes/heart failure do not substitute for FMD |
| Effect or condition | Improvement in flow-mediated dilation in adults at cardiovascular risk |
| Primary endpoint | Brachial FMD (%); percentage-point change distinguished from relative percent |
| Comparator | Placebo; nonrandomized healthy controls excluded from the treatment contrast |
| Duplicate-detection key | vitamin-c|oral|cardiovascular-risk-adults|flow-mediated-dilation-improvement|brachial-fmd |
Gap Measurement · Verdict 3018 · C 50
What the research actually shows
Small placebo-controlled studies measured ultrasound vascular responsiveness, not infarction, stroke or anatomical reversal of disease.
Why this is classified as C (50)
The surrogate results conflict across populations, assays, and durations. One verified strength with EX and B2 limits gives C with 50 points.
Counterpoint. An acute positive response can coexist with uncertain sustained efficacy.
Rejudgment record. Independent Codex cross-check — One page, one route, one population, one claim, one principal comparator
Scoring profile behind this grade
| Endpoint | S | Surrogate marker - laboratory or imaging measures |
| Replication | R0 | Trials conflict in direction |
| Independence | I2 | Decisive evidence is publicly or non-profit funded |
| Effect size | EX | The clinical size of the effect could not be judged |
| Precision | CX | No pooled confidence interval could be confirmed |
The scoring table and the verdict agree (C).
Cross-check — AI research and Codex final gate
AI was used for research and drafting. Blind grading, adversarial audit, and the methodology boundary rules were then reapplied before Codex performed the final evidence, grade, copy, and build checks. If a grade cannot be narrowed, both evidence positions and their reasons are published.
Evidence Table
| Study | Design | Sample | Funding | Endpoint | Result | Weight |
|---|---|---|---|---|---|---|
| Long-term ascorbic acid administration reverses endothelial vasomotor dysfunction in patients with coronary artery disease. | Double-blind CAD RCT | 46 | Detailed independence unverified | FMD; prior hierarchy unverified | C6.6→10.1→9.0%;placebo8.6→7.8→7.9%;repeated ANOVA P=.005. Calculated30-day change difference+3.1percentage points,not a publishedCI | CAD signal,not clinical events |
| Effect of ascorbic acid treatment on conduit vessel endothelial dysfunction in patients with hypertension | Hypertension RCT FMD report | 39 | Public/charity grants and an ACC/Merck fellowship | FMD | Acute and sustained benefit not demonstrated; exact netCI unverified | Related to B1,not a new independent cohort |
| Oral vitamin C and endothelial function in smokers: short-term improvement, but no sustained beneficial effect | Double-blind smoker crossover RCT | 1 | Public/university plus Blackmores support | FMD | Acute2.8±2.0→6.3±2.8%,P<.001;8-week placebo comparison P=.26. Values areSD;8-week SD differs between abstract/table | Acute and sustained results differ; total schedule20weeks |
Receipt — 5 References
Of 5 cited sources, 3 had limited original-page access (blocked or summary-only) and were verified via index/summary, marked partial; the rest were verified at the original page. As of 2026-09-07.
Gokce N et al.. Long-term ascorbic acid administration reverses endothelial vasomotor dysfunction in patients with coronary artery disease.. Circulation. 99(25):3234–3240. 1999. PMID: 10385496; DOI: 10.1161/01.CIR.99.25.3234.
partialDuffy SJ et al.. Effect of ascorbic acid treatment on conduit vessel endothelial dysfunction in patients with hypertension. Am J Physiol Heart Circ Physiol. 280(2):H528–H534. 2001. PMID: 11158948; DOI: 10.1152/ajpheart.2001.280.2.H528.
partialRaitakari OT et al.. Oral vitamin C and endothelial function in smokers: short-term improvement, but no sustained beneficial effect. J Am Coll Cardiol. 35(6):1616–1621. 2000. PMID: 10807468; DOI: 10.1016/S0735-1097(00)00576-3.
partialAshor AW et al. Effect of vitamin C on endothelial function in health and disease: a systematic review and meta-analysis of randomised controlled trials. Atherosclerosis. 2014. PMID: 24792921.
checkedDarko D et al. Lack of effect of oral vitamin C on blood pressure, oxidative stress and endothelial function in Type II diabetes. Clin Sci. 2002. PMID: 12241530. DOI: 10.1042/cs1030339.
checkedResearch and draft: AI used · Cross-check: blind grading and adversarial audit
Final verification and publication gate: Codex · Verification cutoff: 2026-09-07 · Corrections: none
Final verification and publication gate: Codex · Verification cutoff: 2026-09-07 · Corrections: none
Cite this verdict
[Chamgap] Oral Vitamin C and Endothelial FMD—Results Differ by Population and Acute Versus Sustained Dosing — Evidence Grade C·50. 5 cited sources checked. Source: https://chamgap.com/en/verdicts/heart/oral-vitamin-c-endothelial-fmd/ · CC BY 4.0CC BY 4.0 — free to use with attribution; do not distort grades, numbers, or verdict meaning.
What this document does and does not do
Chamgap is an information source. It reports what research has and has not confirmed; it does not tell readers what to take or buy. That decision belongs to readers and, when needed, medical or legal professionals. This verdict reflects literature available up to the search date and may change as new research appears. Nothing here is medical advice.