How does vitamin C lower uric acid levels?

How Vitamin C Lowers Uric Acid

Vitamin C supplementation can reduce serum uric acid levels by approximately 0.35 mg/dL (20.8 μmol/L) through its uricosuric effect, though this effect is modest compared to standard urate-lowering therapies. 1

Mechanisms of Action

Vitamin C lowers serum uric acid through several physiological mechanisms:

1. Uricosuric Effect: Vitamin C competes with uric acid for reabsorption in the kidney tubules, promoting increased urinary excretion of uric acid

2. Reduced Uric Acid Production: Vitamin C may inhibit xanthine oxidase activity, the enzyme responsible for converting xanthine to uric acid

3. Antioxidant Properties: As an antioxidant, vitamin C may reduce oxidative stress that can contribute to hyperuricemia

Evidence for Uric Acid Reduction

The evidence supporting vitamin C's uric acid-lowering effect comes from several studies:

• A systematic review of 13 trials showed that vitamin C supplementation reduced serum urate levels by an average of 0.35 mg/dL (20.8 μmol/L) 1

• A double-blinded placebo-controlled randomized trial demonstrated that 500 mg/day of vitamin C for 2 months significantly reduced serum uric acid levels by 0.5 mg/dL compared to placebo 2

• A prospective study of 46,994 men found that higher vitamin C intake was associated with a lower risk of gout, with a 45% risk reduction in those taking ≥1500 mg/day compared to <250 mg/day 3

Dose-Response Relationship

The effect of vitamin C appears to be dose-dependent:

• Modest effects begin at 500 mg/day
• More significant reductions occur at higher doses (1000-1500 mg/day)
• The effect is more pronounced in individuals with higher baseline uric acid levels 4

Clinical Relevance

Despite these findings, current clinical guidelines do not strongly support vitamin C supplementation for gout management:

• The 2020 American College of Rheumatology guidelines conditionally recommend against vitamin C supplementation for patients with gout 1

• The effect size of vitamin C (0.35 mg/dL reduction) is considerably smaller than that of standard urate-lowering therapies like allopurinol, which can reduce uric acid by 1-3 mg/dL 1

Important Considerations

• Paradoxical Effect: High-dose vitamin C (>1000 mg daily) can actually increase the risk of calcium oxalate stone formation by 40% in men, as vitamin C can be metabolized to oxalate 1

• Caution in Stone Formers: Calcium stone formers with hyperoxaluria should discontinue vitamin C supplements due to this increased risk 1

• Individual Response: The uric acid-lowering effect appears more pronounced in those with higher baseline uric acid levels 4

While vitamin C supplementation may provide a modest benefit for uric acid reduction, it should not replace standard urate-lowering therapies for patients with gout or significant hyperuricemia.