The Effect of Vitamin C Supplements on Urinary Stone Risk: A Systematic Review and Meta-Analysis.
Ala'a Farkouh, Evan Seibly, Matthew I Buell et al.
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In 30 seconds
This systematic review and meta-analysis examined interventional studies of vitamin C supplementation and 24-hour urinary stone-risk parameters in stone formers and nonstone formers. Nine studies were included after screening 808 titles. Supplementation was associated with higher urinary oxalate: the pooled mean difference was 9.72 mg/24 h versus baseline (p < 0.001) and 6.45 mg/24 h versus placebo (p < 0.001). Subgroup analyses found increased oxalate in both populations, while urinary citrate and calcium showed no significant change. The authors suggest the oxalate increase may contribute to stone formation or worsen presentation.
Key findings
- Urinary oxalate increased by 9.72 mg/24 h versus baseline after vitamin C supplementation (p < 0.001).
- Compared with placebo, supplementation increased urinary oxalate by 6.45 mg/24 h (p < 0.001).
- Oxalate increased in both stone formers and nonstone formers; urinary citrate and calcium were not significantly affected.
Why it matters
Urinary oxalate is a parameter associated with stone formation, and the pooled findings indicate that vitamin C supplementation can raise it in people with and without a history of stones. This provides a potential mechanism by which supplementation could contribute to stone formation or worsen stone presentation, although the review assessed urinary parameters rather than stone outcomes.
What to keep in mind
Only nine studies were included, and the analyses focused on 24-hour urinary parameters rather than clinical stone outcomes.