Cranberry Extract
Vaccinium macrocarpon
TL;DR
Cranberry reduces recurrent urinary tract infections in women with a history of them, provided the product delivers at least 36 mg/day of proanthocyanidins. It prevents bacterial adhesion — it does not treat an established infection, and it does not acidify urine meaningfully.
Ideal For
- Women with recurrent uncomplicated UTIs
- Post-coital UTI prophylaxis
- Children with recurrent UTI, under paediatric guidance
- People undergoing urological procedures
Avoid If
- Taking warfarin
- History of calcium oxalate kidney stones
- Using it in place of antibiotics for an active UTI
- Catheterised or institutionalised elderly, where evidence shows no benefit
Frequently Asked Questions
Overview
Cranberry has swung between folk remedy and dismissed placebo for two decades, and the reason is dosing. The active constituents are A-type proanthocyanidins, and older negative trials frequently used juice or capsules delivering far below the roughly 36 mg/day threshold at which anti-adhesion activity is measurable in urine. When the 2023 Cochrane update analysed adequately dosed products, cranberry reduced the risk of recurrent UTI in women with recurrent infections, in children, and in people undergoing urological interventions — while showing no benefit in elderly institutionalised populations or those with catheters, where the pathophysiology differs. The mechanism also explains its limits precisely: preventing bacteria from sticking to the bladder wall is a prophylactic action. Once an infection is established and bacteria are already adherent and replicating, cranberry has nothing to offer and antibiotics are required.
How It Works
- A-type PACs deform E. coli P-fimbriae, preventing urothelial attachment
- Unattached bacteria are flushed out on voiding
- Does not meaningfully acidify urine, despite the common claim
- Prophylactic only — no effect on an established infection
Quick Facts
- 36 mg/day of PACs is the effective threshold
- Prevents adhesion; does not treat active infection
- Does not work by acidifying urine
- No benefit shown in catheterised or institutionalised elderly
Benefits & Outcomes
No linked outcomes yet. Research is ongoing.
Health Concerns Addressed
No linked health concerns yet.
Supporting Research9 studies
The effect of anthocyanins in Vaccinium myrtillus on improving vision under low light conditions
Nakaishi H, Matsumoto H, Tominaga S +1 more
In a small placebo-controlled crossover study, a single dose of bilberry anthocyanin extract produced a measurable improvement in dark adaptation and reduced glare recovery time compared with placebo, with effects appearing within hours of dosing.
Cranberries for Preventing Urinary Tract Infections
Williams G, Stothart CI, Hahn D +3 more
Cranberry products reduced the risk of symptomatic, culture-verified UTI in women with recurrent UTIs (RR 0.74) and in children (RR 0.46).
Cranberry Reduces the Risk of Urinary Tract Infection Recurrence in Otherwise Healthy Women: A Systematic Review and Meta-Analysis
Fu Z, Liska D, Talan D +1 more
Cranberry (Vaccinium spp.) ... reduces the risk of UTI recurrence in otherwise healthy women.
Whole cranberry fruit powder supplement reduces the incidence of culture-confirmed urinary tract infections in females with a history of recurrent urinary tract infection: A 6-month multicenter, randomized, double-blind, placebo-controlled trial
Stonehouse W, Benassi-Evans B, Bednarz J +1 more
Whole cranberry powder capsules reduced the incidence of culture-confirmed urinary tract infections in females with a history of recurrent urinary tract infection.
Cranberry Juice Fails to Prevent Recurrent Urinary Tract Infection: Results from a Randomized Placebo-Controlled Trial
Barbosa-Cesnik C, Brown MB, Buxton M +3 more
Recurrence rates were 19.3% with cranberry versus 14.6% with placebo, a non-significant difference favouring placebo.
Consumption of a cranberry juice beverage lowered the number of clinical urinary tract infection episodes in women with a recent history of urinary tract infection
Maki KC, Kaspar KL, Khoo C +2 more
Consumption of a cranberry juice beverage lowered the number of clinical urinary tract infection episodes in women with a recent history of urinary tract infection.
Randomized, placebo-controlled, double-blinded study of prophylactic cranberries use in women with recurrent uncomplicated cystitis
Tsiakoulias E, Gravas S, Hadjichristodoulou C +2 more
In response to intervention, the number of UTIs was significantly lower (Incidence rate ratio) in the cranberry group.
Cranberry juice capsules and urinary tract infection after surgery: results of a randomized trial
Foxman B, Cronenwett AE, Spino C +2 more
The occurrence of UTI was significantly lower in the cranberry treatment group compared with the placebo group (15 of 80 [19%]).
Suppression of Helicobacter pylori infection by daily cranberry intake: A double-blind, randomized, placebo-controlled trial
Li ZX, Ma JL, Guo Y +2 more
H. pylori-negative rates ... at week 8 were 7.35%, 7.58%, 4.48%, and 20.00%, respectively.
Safety Information
Potential Side Effects
Well tolerated. Gastrointestinal upset and diarrhoea at high doses; juice forms contribute significant sugar and oxalate load.
Contraindications
Never substitute for antibiotic treatment of an active urinary tract infection, which can ascend to the kidneys. Caution in oxalate stone formers.
Drug Interactions
- Warfarin — case reports of raised INR
- Aspirin — theoretical additive antiplatelet effect from salicylates
- Nephrotoxic drugs — high oxalate loads warrant caution in renal impairment
Pregnancy & Breastfeeding
Pregnancy: likely_safe
Breastfeeding: likely_safe
Dosage Guidelines
Dosage Used in Studies
36-72 mg
Best Time to Take
Once or twice daily, with an evening dose useful before overnight urine retention
Best Form
Extract standardised to A-type proanthocyanidins by the DMAC method
Bioavailability
PACs are poorly absorbed systemically, which is irrelevant here — enough metabolites reach urine to produce the anti-adhesion effect.
Forms Compared
PAC-standardised capsule
Unsweetened juice
Whole fruit powder
Food & Timing
With or without food; drink adequate water alongside.
Medical Disclaimer
The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.
Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.