The Effect of Vitamin C Supplements on Urinary Stone Risk: A Systematic Review and Meta-Analysis

Farkouh A, Seibly E, Buell MI, Jhang D, Amasyali AS, Okhunov Z, Baldwin DD · Journal of Endourology

Pools the interventional evidence behind the cohort signal and confirms the mechanism directly. Urinary oxalate rose by a mean 9.72 mg/24 h against baseline and 6.45 mg/24 h against placebo (both p<0.001), in stone formers and non-stone formers alike. Urinary citrate and calcium, the other two levers on stone risk, were unaffected — so the whole of vitamin C's effect on stone chemistry runs through oxalate.

Population

Nine interventional studies of vitamin C supplementation with 24-hour urinary parameters, in stone formers and non-stone formers

Intervention

Vitamin C supplements

Comparator

Baseline or placebo

Limitations

Nine studies, heterogeneous in dose and duration, pooling a biochemical risk marker rather than stone events — the meta-analysis measures urine, not colic. Doses are not separated in the pooled estimate, so it cannot say what 1 g/day specifically does. Search ends February 2023.