About D-Mannose
A simple sugar (glucose epimer) marketed for urinary tract health. Mechanism is plausible — excreted in urine, it blocks E. coli FimH fimbriae from adhering to the bladder wall. Early enthusiasm came from a 2014 secondary-care RCT (Kranjčec, n=308) showing reduced recurrence comparable to nitrofurantoin, but rigorous recent evidence is negative: the 2024 MERIT trial (JAMA Internal Medicine, n=598, double-blind primary care) found no benefit over placebo (51.0% vs 55.7%, P=.26), and a 2024 meta-analysis (6 RCTs, n=1,167) found no reduction in recurrent UTI vs control or antibiotics. Generally well tolerated; high doses can cause bloating/loose stool. Not an essential nutrient. Distinct from Manno-oligosaccharides (MOS), a yeast-derived prebiotic polymer.
What D-Mannose supports
- Marketed for urinary tract health (recent large RCTs found no benefit over placebo)
- May block E. coli from adhering to the bladder wall (mechanistic)
How much D-Mannose to take
The RDA prevents deficiency. The effective range is what clinical trials used to actually move the outcome.
Effective
1000–2000
mg
Prevention dose ~1.5–2 g/day (trials ranged 420 mg–2 g); acute UTI protocols use more (up to ~3 g, 2–3×/day).
Clinical evidence
Limited clinical evidence. 2024 MERIT RCT and a 2024 meta-analysis found no benefit over placebo for recurrent UTI prevention, despite popularity
Reference