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

⚖️

Scoring transparency

All scores computed by a 7-layer evidence engine — fully auditable

Raw score 0.48

← counter-evidence / ineffectiveeffective / strong evidence →

Final grade

C · Published with Warning

Confidence

89%

Highly consistent evidence

Evidence level

Cochrane high-quality SR/MA

How strongly each layer supports this effect

lower = less supportive

L2 PubMedPrimary literature

0.45

L3 MechanismPlausibility

0.45

L1 ExamineGlobal benchmark

0.50

L11 AI re-checkIndependent read

0.50

L5 Clinical bodiesAuthoritative stance

0.55

Against Mixed Supports

▸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)

PMID: 34767649 2021 Cochrane Review n = 40

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.

🟢 High quality Academic Effect size: MD 0.10 mmol/L (95% CI 0.06–0.15) favoring allopurinol over vitamin C; vitamin C effect on gout flares not assessed

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Effect of oral vitamin C supplementation on serum uric acid: a meta-analysis of randomized controlled trials

PMID: 21671418 2011 統合分析 n = 556

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.

Government Effect size: WMD -0.35 mg/dL (95% CI -0.66 to -0.03), P=0.032, I²=77%

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Association between Oral vitamin C supplementation and serum uric acid: A meta-analysis of randomized controlled trials

PMID: 34280483 2021 統合分析 n = 1,013

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).

Academic

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Effects of vitamin C supplementation on gout risk: results from the Physicians' Health Study II trial

PMID: 35575611 2022 RCT (double-blind) n = 14,641

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).

Government Effect size: HR 0.88 (95% CI 0.77–0.99), P=0.04

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Clinically insignificant effect of supplemental vitamin C on serum urate in patients with gout: a pilot randomized controlled trial

PMID: 23681955 2013 RCT (open-label) n = 40

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.

Academic Effect size: −0.23 mg/dL (vitamin C) vs −1.9 mg/dL (allopurinol), P<0.001

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↗

✓PMID 100% verifiedevery citation checked via NCBI Entrez

🔬5 PubMed studiesindependently re-checked by multiple sub-agents

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