Cranberry for Kidney Stones
Cranberry is not a remedy for kidney stones. For people prone to calcium-oxalate or uric-acid stones, concentrated cranberry juice and tablets more likely raise stone risk than lower it, and no medical body recommends cranberry for stone prevention.
Why this grade7-layer evidence engine
This is a counter-evidence grade: the real question is whether cranberry helps or harms stone formers, and the best clinical signal points to harm or no benefit. The most informative trial, an NIH-funded randomized crossover (PMID 16006907, n=24), found 1 liter/day of cranberry juice significantly raised urinary calcium and oxalate, increased calcium-oxalate supersaturation by about 18%, and lowered urinary pH — a profile that favors both calcium-oxalate and uric-acid stones. Two tablet studies (PMID 30039387, n=15; PMID 11164137, n=5) concordantly showed urinary oxalate rising, with authors advising stone-prone patients to avoid cranberry.
The evidence is genuinely conflicting in one respect: a trial of more dilute juice (PMID 14616463, n=20) found the opposite favorable pattern, with oxalate falling and citrate rising, and a 2021 USP safety review (PMID 34015833) judged the overall data too inconsistent to firmly link cranberry to stones. Direction appears to hinge on formulation and dose, and tablet effects are partly confounded by added vitamin C, which independently raises oxalate.
Regulators and clinics offer no support for stones specifically. The FDA's qualified health claim covers only recurrent UTIs in women and rests on 'limited and inconsistent' evidence, while Mayo Clinic notes a study showing cranberry juice raises stone-formation risk and stops short of recommending it. With clinic consensus cautionary, all harm-signal trials small and short (n=5-24, 1-2 weeks), and only urinary surrogates rather than actual stones measured, the grade stays Unverified and is published as counter-evidence.
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸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 = 0.302
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 無高階證據可裁決
- tier_strict_requirement_check — D 級條件未達 (需 E1-E3 negative；實際 E6)
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status