Legacy AI grade · Sources dated 2026-06-09. Not expert reviewed. Coverage is limited to the listed sources. About the new summary workflow
Vitamin C for Gout
Verdict: Published with Warning
Across 5 PubMed studies, the evidence for Vitamin C in Gout grades Tier C — weak evidence. Effective, but with safety or population caveats.
C 🟠 C Weak Evidence Published with Warning
Why this grade7-layer evidence engine
Vitamin C may lower serum uric acid modestly, but gout-flare prevention is unproven. Two uric-acid meta-analyses (PMID 21671418, 34280483) likely overlap and show small effects.
The Cochrane anchor (PMID 34767649, CD010156) covers dietary supplements for chronic gout broadly, not vitamin-C monotherapy — a scope stretch for the E1 label.
Tier C with warning reflects surrogate uric-acid changes without hard gout-outcome benefit. Vitamin C is not a substitute for urate-lowering therapy.
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Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditableRaw score 0.48
D
C
B
A
S
← counter-evidence / ineffectiveeffective / strong evidence →
Final grade
C · Published with Warning
Confidence
89%
Highly consistent evidence
Evidence level
E3
PMID 34767649 is Cochrane CD010156 on dietary supplements for gout, not vitamin-C-specific
▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.485
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 positive (1 篇 > 0 negative)
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status
PubMed studies (5)L2 · primary research & systematic reviews
Dietary supplements for chronic gout (Cochrane Database Syst Rev, CD010156.pub3)
Finding: For established gout, the only vitamin C trial (n=40, high risk of bias) showed allopurinol lowered serum uric acid substantially more than vitamin C (MD 0.10 mmol/L, 95% CI 0.06 to 0.15, low-quality evidence); authors concluded there is no high-quality evidence supporting or refuting vitamin C for chronic gout.
View on PubMed Effect of oral vitamin C supplementation on serum uric acid: a meta-analysis of randomized controlled trials
Finding: Vitamin C significantly lowered serum uric acid by a small -0.35 mg/dL (95% CI -0.66 to -0.03, P=0.032) with substantial heterogeneity (I²=77%); authors noted future trials are needed to show whether this reduces hyperuricemia or prevents gout.
View on PubMed Association between Oral vitamin C supplementation and serum uric acid: A meta-analysis of randomized controlled trials
Finding: Pooled across 16 RCTs (n=1,013), oral vitamin C produced a statistically significant reduction in serum uric acid with no significant publication bias, with larger effects in placebo-controlled trials and participants <65 years; the exact pooled WMD value could not be verified from the open abstract (full text paywalled).
View on PubMed Effects of vitamin C supplementation on gout risk: results from the Physicians' Health Study II trial
Finding: Vitamin C 500 mg/day modestly reduced new gout diagnoses by 12% versus placebo (HR 0.88, 95% CI 0.77–0.99, P=0.04; 8.0 vs 9.1 events per 1000 person-years), with the effect concentrated in men with BMI <25 (P-interaction=0.01).
View on PubMed Clinically insignificant effect of supplemental vitamin C on serum urate in patients with gout: a pilot randomized controlled trial
Finding: In patients who actually have gout, vitamin C 500 mg/day produced a clinically insignificant urate reduction far smaller than allopurinol (mean reduction 0.014 mmol/L [0.23 mg/dL] with vitamin C vs 0.118 mmol/L [1.9 mg/dL] with allopurinol, P<0.001), despite confirmed rises in plasma ascorbate.
View on PubMed Regulatory & authoritative positionsL4/L5 · FDA / EMA / NIH ODS / Cochrane / Mayo …
L4a US FDA
Supportive
Consumption of antioxidant vitamins may reduce the risk of certain kinds of cancer. source↗
L4b EU EFSA
Supportive
A cause and effect relationship has been established between the dietary intake of vitamin C and protection of DNA, proteins and lipids from oxidative damage. source↗
L4c UK NHS
Cautious
You should be able to get all the vitamin C you need by eating a varied and balanced diet. If you take vitamin C supplements, do not take too much as this could be harmful. source↗
L4d TW TFDA / 衛福部
Supportive
成人每日需要的攝取量為100毫克、孕婦每日120毫克、哺乳媽媽每日140毫克 source↗
L4e WHO
Neutral
Vitamin E and C supplementation is not recommended for pregnant women to improve maternal and perinatal outcomes. source↗
L5a NIH Office of Dietary Supplements
Supportive
Vitamin C plays an important role in immune function and improves the absorption of nonheme iron. source↗
L5b Mayo Clinic
Supportive
Vitamin C may help lower uric acid levels. Talk to your healthcare professional about whether a 500-milligram vitamin C supplement would be good for you. source↗
L5d Harvard Health
Supportive
You can also increase your intake of foods that have been shown to lower uric acid levels, like coffee (regular or decaf) and cherry juice, as well as increasing your vitamin C intake through supplements or foods, such as bell peppers, broccoli, strawberries, and oranges. source↗
L5e Specialty Society (condition-mapped)
Against
The 2020 American College of Rheumatology guideline conditionally recommends against adding vitamin C supplementation for patients with gout, regardless of disease activity. The evidence available on vitamin C was insufficient to support continued recommendation for its use in patients with gout; two small RCTs showed clinically insignificant changes in serum urate concentrations. source↗