D-Mannose for Urinary Tract Infection
D-Mannose is not a reliable way to prevent recurrent urinary tract infections: the largest, most rigorous trial found no benefit and pooled analyses are inconclusive. It appears safe, so some women may choose to try it, but it should never replace proven prevention or the antibiotics needed for an active infection.
Why this grade7-layer evidence engine
The grade is held down by a sharp split in trial quality. An early open-label RCT (Kranjcec 2014, PMID 23633128, n=308) reported a large protective effect rivaling the antibiotic nitrofurantoin, but its unblinded design carries a high risk of bias. The much larger, double-blind, placebo-controlled MERIT trial (PMID 38587819, n=598) was null: 51.0% of the D-Mannose group versus 55.7% on placebo still developed a UTI (p=0.26).
Two 2025 meta-analyses confirm the uncertainty rather than resolving it. Pooled risk ratios of 0.44 (PMID 41195062) and 0.57 (PMID 41004704) both crossed 1 and were not statistically significant, with very high between-trial heterogeneity (I-squared around 90%). In postmenopausal women the effect was essentially absent (RR 0.94). The 2022 Cochrane review (PMID 36041061) found little to no usable evidence and rated the certainty as very low.
Regulators and clinicians echo this caution. The UK NHS lists D-Mannose only as an optional self-care sugar you can buy as powder or tablets, not a medicine; the EU's EFSA rejected the sole D-Mannose UTI health claim for insufficient evidence; the US FDA issued a warning letter against UTI-prevention marketing; and the 2025 AUA/CUA/SUFU statement says monotherapy may not be effective. Because side effects are minor, mainly mild diarrhea, it earns a weak rather than a fully refuted grade.
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 = 0.485
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高階證據未達主導 (0 positive vs 1 negative)，由 raw_score 決定
- 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