Cranberry (Large-Fruited Cranberry)

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1. What Cranberry Is

Cranberry (Vaccinium macrocarpon) is the fruit of the large-fruited cranberry, an evergreen shrub from the heath family. The berry is rarely eaten raw but is processed into juice, dried fruit, powder or extract. In herbal medicine it has long been used for urinary tract complaints. Its constituents include organic acids, sugars, vitamins and a broad range of polyphenols, among them anthocyanins, flavonols and proanthocyanidins.

For urinary tract infection research a particular type of proanthocyanidins with A-type linkages is considered especially relevant because it can inhibit the attachment of uropathogenic Escherichia coli to bladder epithelial cells. This anti-adhesive effect is the best-studied mechanism and has been demonstrated in urine samples after cranberry consumption. Other constituents such as flavonols and phenolic acids are linked to antioxidant and vascular effects. Exact composition varies considerably according to cultivar, cultivation, processing and dosage form, which limits comparability of studies.

2. What the Studies Show in Detail

The key human studies and the most important reviews — by indication, with population, duration, preparation, measure and result as reported in the original papers. Numbers appear only where the study states them.

Distribution of controlled human studies by indication — the numbers are not additive because one study may be assigned to several indications:

Gut and Microbiome

The randomised controlled study by Kontiokari and colleagues examined 150 women with a urinary tract infection caused by Escherichia coli. Participants received either 50 ml of a cranberry-lingonberry juice concentrate daily for six months, 100 ml of a Lactobacillus-GG drink on five days per week for one year, or no intervention. The primary endpoint was the first recurrent infection, defined as bacterial growth of ≥10^5 colony-forming units per ml in mid-stream urine. After twelve months the cumulative recurrence rate differed significantly between groups (P=0.048). After six months 8 (16 %) women in the cranberry-lingonberry group, 19 (39 %) in the Lactobacillus group and 18 (36 %) in the control group had at least one recurrent infection. This corresponds to an absolute risk reduction of 20 % in the cranberry-lingonberry group versus the control group (95 % CI 3 % to 36 %, P=0.023; number needed to treat = 5, 95 % CI 3 to 34) 23. The study was open-label and therefore not blinded, which limits its strength of evidence.

A randomised, double-blind, placebo-controlled study in 295 asymptomatic children aged 6 to 16 years who tested positive for Helicobacter pylori examined the effect of cranberry juice and the probiotic Lactobacillus johnsonii La1. The children received 200 ml cranberry juice and 80 ml La1 product daily for three weeks in four groups: cranberry juice/La1, placebo juice/La1, cranberry juice/heat-inactivated La1 and placebo juice/heat-inactivated La1. Eradication rates differed significantly: 1.5 % in the control group versus 14.9 %, 16.9 % and 22.9 % in the La1, cranberry and cranberry/La1 groups (P<0.01). The study shows superior eradication in the intervention groups; however, follow-up after a one-month wash-out phase was planned only for children who tested negative, which limits statements on durability.

An acute double-blind randomised controlled study in 10 healthy men examined the uptake, metabolism and excretion of cranberry polyphenols at different doses. The participants received cranberry juices with 409, 787, 1238, 1534 and 1910 mg total polyphenols. Plasma and urine were analysed by UPLC-Q-TOF-MS. 60 metabolites were identified, including cinnamic acids, dihydrocinnamic acids, flavonols, benzoic acids, phenylacetic acids, benzaldehydes, valerolactones, hippuric acids, catechols and pyrogallols. The small sample size and the acute administration do not permit any statement on long-term effects.

A randomised, double-blind crossover study in 11 healthy adults examined the influence of cranberry on the gut microbiota in the context of an animal-based diet. The participants consumed for five days each a control diet (animal-based diet plus 30 g/day placebo powder) and a cranberry diet (animal-based diet plus 30 g/day freeze-dried cranberry powder). Stool, urine and blood samples were collected before and after each intervention phase. Compared with the pre-control diet, the control diet altered 46 taxonomic clades, including an increase in Firmicutes and a decrease in Bacteroidetes, and raised bacteria-derived deoxycholic acid as well as lowered acetate and butyrate in stool. Compared with the post-control phase, the cranberry diet altered 9 taxonomic clades, including a decrease in Firmicutes and an increase in Bacteroidetes. Furthermore, the cranberry diet attenuated the control-diet-induced rise in secondary bile acids and the fall in short-chain fatty acids and raised urinary anthocyanins and bacteria-derived phenolic acids. No changes were found in faecal trimethylamine and p-cresol 42. The short intervention duration and the small sample size limit generalisability.

The systematic review and meta-analysis by Wang and colleagues identified 13 randomised controlled trials with 1616 participants, of which 10 studies with 1494 participants entered the quantitative synthesis. The pooled risk ratio (RR) for cranberry users versus non-users was 0.62 (95 % CI 0.49–0.80) with moderate heterogeneity (I²=43 %) after exclusion of one outlier study. In subgroup analyses, cranberry products appeared more effective in women with recurrent urinary tract infections (RR 0.53; 95 % CI 0.33–0.83; I²=0 %) and in female populations (RR 0.49; 95 % CI 0.34–0.73; I²=34 %) 46. The authors point to the heterogeneity of the included studies.

The Cochrane review by Jepson and Craig from 2012 included 24 studies (six crossover studies, eleven parallel-group studies with two arms, five others). The authors calculated risk ratios where possible; otherwise a narrative synthesis was performed. Quality was assessed with the Cochrane risk-of-bias tool 13. The results suggest a certain protective effect in women with recurrent urinary tract infections, yet many questions remain open, particularly regarding optimal dosage and effects in other populations.

Hypothesis The observed effects on the gut microbiota and the anti-adhesive properties of cranberry polyphenols could contribute to the prevention of urinary tract infections via modulation of intestinal colonisation by uropathogenic pathogens. However, the data on this mechanism of action are still at an early stage; long-term studies in larger populations that link microbial composition and clinical infection rates are still outstanding.

Heart and Circulation

A placebo-controlled crossover study in 44 patients with coronary heart disease examined the effect of cranberry juice on vascular function. The participants consumed 480 ml of a double-concentrated cranberry juice (54 % juice, 835 mg total polyphenols, 94 mg anthocyanins) or a matched placebo beverage daily for four weeks, with a two-week washout period between the beverages. Vascular function was measured before and after each beverage, with re-testing ≥12 hours after the last beverage. Mean (±SD) carotid-femoral pulse-wave velocity, a measure of central aortic stiffness, decreased after cranberry juice (8.3 ± 2.3 to 7.8 ± 2.2 m/s) in contrast to an increase after placebo (8.0 ± 2.0 to 8.4 ± 2.8 m/s) (P=0.003). Flow-mediated dilatation of the brachial artery and digital pulse-wave amplitude were also measured 35. The study was designed as both acute and chronic, yet the acute part was not placebo-controlled (n=15).

A double-blind, randomised, controlled crossover study in 10 healthy men examined the dose- and time-dependent effect of cranberry juice on vascular function. Flow-mediated dilatation (FMD), blood pressure, pulse-wave velocity and augmentation index were measured at baseline and at 1, 2, 4, 6 and 8 hours after consumption. Dose-dependent increases in FMD were observed at all time points with a peak at 4 hours and maximal effects with a juice containing 1238 mg total polyphenols. 60 metabolites were quantified in plasma; twelve polyphenol metabolites correlated significantly with the FMD increases, including ferulic-acid and caffeic-acid sulphates, quercetin-3-O-β-D-glucuronide and a γ-valerolactone sulphate 40.

Hypothesis The improvement in endothelial function by cranberry polyphenols could lower cardiovascular risk in the long term. However, the studies available are acute or short-term and conducted in small populations; studies with clinical endpoints such as myocardial infarction or stroke are still outstanding. What remains to be clarified are long-term studies in larger populations with hard cardiovascular endpoints.

Immune System

A multicentre, randomised, double-blind placebo-controlled study in 32 volunteers from Japan, Hungary, Spain and France examined the dose-response of cranberry powder, standardised to proanthocyanidins (PACs), on anti-adhesive activity in urine. Two bioassays (a mannose-resistant haemagglutination assay and a human T24 epithelial-cell-line assay) assessed ex-vivo bacterial anti-adhesion activity in urine samples. The results showed significant bacterial anti-adhesion activity in urine samples from volunteers who had consumed cranberry powder compared with placebo (p<0.001). This inhibition was dose-dependent, prolonged (up to 24 hours with 72 mg PAC) and increased with the amount 36. A preclinical in-vivo Caenorhabditis elegans model was used to examine the influence of the cranberry regimen on E. coli virulence; an effect in humans is not inferred from this. The study is limited to ex-vivo and in-vivo models; clinical endpoints were not assessed.

A double-blind, randomised, placebo-controlled crossover study in 20 healthy volunteers (10 men, 10 women) examined anti-adhesion activity in urine after single consumption of cranberry juice. Each volunteer received in random order four regimens: (1) 250 ml placebo plus 500 ml mineral water, (2) 750 ml placebo, (3) 250 ml cranberry juice plus 500 ml mineral water, (4) 750 ml cranberry juice, each with dinner, with a washout period of at least 6 days between regimens. The first morning urine after consumption was collected and used for bacterial growth. Six uropathogenic E. coli strains (all with type-1 pili; three positive for the gene marker for P-fimbriae papC and three negative for papC) were cultured in the urine samples and tested for their ability to adhere to the T24 bladder cell line in vitro. There were no significant differences in pH or specific gravity between the urine samples after cranberry or placebo consumption 43. The study shows an acute effect on adhesion, yet no clinical infection rates.

Hypothesis The anti-adhesive effect of cranberry polyphenols in urine could reduce the attachment of uropathogenic E. coli to the uroepithelium and thereby prevent urinary tract infections. However, the anti-adhesion studies described here are acute and measure surrogate parameters; they did not assess clinical endpoints. Studies directly linking anti-adhesive activity with the incidence of urinary tract infections remain to be conducted.

Inflammatory Processes

A randomised, double-blind, placebo-controlled study in participants with metabolic syndrome (n=15–16 per group) examined the effect of low-calorie cranberry juice (480 ml/day) over 8 weeks on cardiovascular risk factors. Anthropometry, blood-pressure measurements, dietary analyses and fasting blood draws were performed at baseline and after 8 weeks. Cranberry juice significantly increased plasma antioxidant capacity (1.5 ± 0.6 to 2.2 ± 0.4 μmol/L [means ± SD], P<0.05) and reduced oxidised LDL and malondialdehyde (120.4 ± 31.0 to 80.4 ± 34.6 U/L and 3.4 ± 1.1 to 1.7 ± 0.7 μmol/L [means ± SD], P<0.05) compared with placebo. However, there were no significant improvements in blood pressure, glucose and lipid profiles, C-reactive protein and interleukin-6. No changes in these parameters were observed in the placebo group 37. The study was small and of short duration; the laboratory values measured are not clinical endpoints.

A double-blind, placebo-controlled parallel-group study with controlled feeding in 30 women and 26 men (mean baseline characteristics: 50 years; weight 79 kg; BMI 28 kg/m²) examined the effect of low-calorie cranberry juice (LCCJ) over 8 weeks. Participants consumed 240 ml LCCJ or a flavour-, colour- and energy-matched placebo beverage twice daily; the beverages contained 173 and 62 mg phenolic compounds and 6.5 and 7.5 g total sugar per 240-ml portion, respectively. Fasting serum triglycerides were lower after LCCJ and showed a treatment×baseline interaction, so that participants with higher baseline triglyceride values were more likely to show a larger treatment effect (1.15 ± 0.04 mmol/L vs. 1.25 ± 0.04 mmol/L; P=0.027). Serum C-reactive protein (CRP) was lower in those who consumed LCCJ than in those who consumed the placebo beverage (ln-transformed values 0.522 ± 0.115 ln(mg/L) vs. 0.997 ± 0.120 ln(mg/L), P=0.0054; corresponding to 1.69 mg/L vs. 2.71 mg/L) 38. The study was limited to 8 weeks.

A randomised, placebo-controlled, double-blind study in 30 type-2 diabetics (16 men, 14 women; mean age 65 ± 1 years) taking oral glucose-lowering medication examined the effect of cranberry extracts over 12 weeks on lipid profiles, oxidised LDL, glycaemic control, components of the metabolic syndrome, C-reactive protein and urinary albumin excretion. LDL cholesterol fell significantly in the cranberry group (from 3.3 ± 0.2 to 2.9 ± 0.2 mmol/l, P=0.005) and the reduction was significantly greater than in the placebo group (-0.4 ± 0.1 vs. 0.2 ± 0.1 mmol/l, P<0.001). Total cholesterol and the total-to-HDL cholesterol ratio also fell significantly (P=0.020 and 0.044) in the cranberry group and the reductions differed significantly from those in the placebo group (P<0.001 and P=0.032). Oxidised LDL, however, did not change significantly. Neither fasting glucose nor glycated haemoglobin improved in either group 39. The study was small and the participants were already taking medication.

A parallel, double-blind, controlled and randomised clinical trial in 41 insulin-resistant, non-diabetic overweight or obese adults examined the effect of strawberry and cranberry polyphenols (SCP) on insulin sensitivity. The experimental group consumed an SCP beverage (333 mg SCP) daily for 6 weeks, while the control group received a flavour-matched control beverage containing 0 mg SCP. Insulin sensitivity was measured by hyperinsulinaemic-euglycaemic clamp technique; glucose tolerance and insulin secretion were assessed by 2-hour oral glucose tolerance test (OGTT). No differences were found in other parameters 41. The study used a mixture of strawberry and cranberry polyphenols, so the effect of the single substance cranberry cannot be isolated.

Hypothesis The observed improvements in inflammatory markers and lipid profiles by cranberry could lower cardiometabolic risk. However, the cited studies are short and conducted in small populations; long-term studies with clinical endpoints are still outstanding. What remains to be clarified are studies that examine the effect of cranberry on hard cardiovascular endpoints in at-risk populations.

Oxidative Stress

A placebo-controlled study in 20 healthy female volunteers aged 18–40 years examined the effect of daily consumption of anthocyanin-rich cranberry juice (750 ml/day) or a placebo beverage over 2 weeks on plasma antioxidant activity and biomarkers of oxidative stress. Fasting blood and urine samples were collected over 4 weeks. Total phenol, anthocyanin and catechin content of the supplements and plasma were measured. Anthocyanin glycosides were identified by tandem mass spectrometry. Vitamin C, homocysteine and reduced glutathione were measured by HPLC. Total antioxidant capacity was determined by electron-spin-resonance spectrometry and FRAP assay. Plasma total cholesterol, HDL, LDL and triglycerides were measured. Glutathione-peroxidase, catalase and superoxide-dismutase activities were determined. The study was small and of short duration; larger controlled studies on the antioxidant question are still outstanding.

Hypothesis The antioxidant properties of cranberry polyphenols could contribute to the reduction of oxidative stress. However, the present study is small and short; larger controlled studies of longer duration on this question are still outstanding. What remains to be clarified are studies that link the antioxidant effect with clinical endpoints.

Safety and Tolerability

An in-vitro and clinical study examined the interaction of flurbiprofen with cranberry juice, grape juice, tea and fluconazole. In human liver microsomes the effect of 4 beverages on CYP2C9 activity was examined using flurbiprofen hydroxylation as the index reaction. In the clinical study 14 healthy volunteers received 100 mg flurbiprofen on 5 occasions in crossover design, with at least 1 week between the 5 trials. Flurbiprofen was preceded in random order by: (1) cranberry-juice placebo (8 oz), (2) cranberry juice (8 oz), (3) brewed tea (8 oz), (4) grape juice (8 oz) and (5) fluconazole, a CYP2C9 inhibitor as positive control, with 8 oz water. Flurbiprofen hydroxylation in vitro was reduced by 2.5 % (vol/vol) brewed tea to 11 % ± 8 % of control, by grape juice to 10 % ± 7 %, by cranberry juice to 56 % ± 16 %, by cranberry-juice placebo to 85 % ± 5 % and by the index inhibitor sulfaphenazole (2.5 μmol/L) to 21 % ± 6 % (P<0.01 for all comparisons versus control) 44. The clinical results are not fully reported in the abstract; the study was small.

Hypothesis The in-vitro data suggest a possible inhibition of CYP2C9 by cranberry juice, which could affect the clearance of drugs such as warfarin. Clinical relevance, however, is unclear because the clinical results are not fully reported. What is missing are clinical studies that examine the interaction of cranberry with CYP2C9 substrates in patients on the corresponding medication.

Metabolism

A controlled study determined the phenolic composition of a commercial cranberry juice (CBJ) using high-performance liquid chromatography and examined the effect of low-calorie and normal-calorie CBJ formulations on the postprandial glycaemic response in healthy humans. The CBJ contained seven phenolic acids, with 3- and 5-caffeoylquinic acid as the main components, and 15 flavonol glycosides, with myricetin-3-galactoside and quercetin-3-galactoside the most abundant. The CBJ proanthocyanidins consisted of three different tetramers and one heptamer, confirmed by MALDI-TOF mass spectrometry. Participants received one of six treatments: nothing (no water/drink), water (480 ml), unsweetened low-calorie CBJ (38 Cal/480 ml), normal-calorie CBJ (280 Cal/480 ml), isocaloric normal-calorie drink (high-fructose corn syrup) or isocaloric low-calorie drink. No significant differences in postprandial blood glucose or insulin were found in the groups that received nothing, water or low-calorie treatments. In contrast, intake of normal-calorie CBJ and normal-calorie control drink led to significantly higher blood glucose concentrations 30 minutes postprandially, although the differences were no longer significant after 180 minutes. Plasma insulin was also measured 45. The study was acute and conducted in healthy humans; the results are not transferable to people with diabetes.

Hypothesis The phenolic compounds in cranberry juice could influence postprandial glycaemia, yet the acute data show no significant effect on blood glucose with low-calorie formulations. What is missing are longer-term studies in humans with impaired glucose tolerance or diabetes that examine the effect of cranberry on glycaemic control.

Overall Picture

Across all areas, cranberry polyphenols can exert diverse biological effects, particularly anti-adhesive, antioxidant and vascular-function-improving actions. Evidence exists for the prevention of urinary tract infections in women with recurrent infections, supported by randomised controlled trials and meta-analyses. For other endpoints such as cardiovascular events, inflammatory markers and metabolic parameters many studies are short in duration and use surrogate parameters, so what is missing are longer-term studies that examine these endpoints in patients.

The heterogeneity of the studies with regard to dosage, preparation and population complicates generalisation. While some studies show significant effects, others remain without effect, which could be attributable to differing bioavailability of the constituents and methodological differences. Research on cranberry is an active field, and the available work provides important indications that must be confirmed by larger, long-term studies with clinical endpoints.

3. How Robust the Research Is

Research on cranberry is broad: of 369 evaluated works, 208 examine humans, of which 145 are controlled. The largest block consists of studies on the immune system (98), followed by safety (36), gut (34), metabolism (23), inflammation (20), cardiovascular system (15), antioxidant markers (14), oncology (13), fatigue (13) and musculoskeletal system (3). The most frequently cited controlled studies deal with urinary tract infections, vascular-related effects and metabolic markers.

It is striking that urinary tract infection prophylaxis, although the best-known area of application, nevertheless shows an inconsistent evidence base: a large randomised study from 2011 reports that cranberry juice could not prevent recurrent urinary tract infections, whereas a non-inferiority study from the same year found no inferiority to antibiotics in premenopausal women. Reviews and meta-analyses from 2007, 2008 and 2012 reach differing assessments, due above all to differences in product, dose and study population.

4. What Is Frequently Claimed — and What the Data Provide

5. Profile: Molecule and Charge

Cranberry (large-fruited cranberry) is not a single molecule but a mixture — there is no molecular formula and no fixed molecular mass. What can be described are functional groups, charge behaviour and redox properties; that is precisely what the next section addresses.

6. Charge, Electrons, Radicals

Electrochemically, radical scavenging is at the forefront with cranberry. An extract achieved more than 85 % free-radical scavenging in cell culture at higher concentrations 25. Directly measured redox or charge values in humans do not supply these statements.

Quercetin bound Fe(2+) at pH 7.2 even more strongly than the well-known Fe(2+)-chelator ferrozine 26; this may possibly be the first example of an oxygen-based ligand with stronger Fe(2+)-affinity than a strong nitrogen-based chelator 26. Quercetin was able to suppress Fenton chemistry completely, both in the micromolar range and in the presence of cellular iron chelators such as ATP or citrate 26. Radical scavenging, by contrast, only partially protected against Fenton-mediated damage, whereas chelation completely inhibited Fenton chemistry 26. It remains open whether these chelation and redox processes can be measured in humans; a controlled investigation with redox markers in blood would be the next step.

7. Interactions with Other Substances

Substances on the platform with which this substance has been jointly investigated or discussed in human studies and reviews — combination, comparison or shared mechanism of action. The figure indicates studies in which both occur.

Ciclosporin is a substrate of CYP3A and P-glycoprotein. When given together with cranberry juice, the ratios of the least-squares means for AUCt, AUCinf and Cmax were 95.0 % (95 % CI 90.3 %–100.1 %), 93.4 % (95 % CI 89.2 %–97.8 %) and 95.2 % (95 % CI 86.9 %–104.2 %) 27. Pomelo juice, but not cranberry juice, altered the pharmacokinetics of ciclosporin 27. For warfarin, inhibition of CYP2C9 was discussed, the principal isoenzyme in the metabolism of S-warfarin 29.

With warfarin, two controlled human studies showed no significant effect. Seven persons with atrial fibrillation on a stable warfarin dose each received 250 ml cranberry juice and placebo for 7 days; no substantial interaction was observed 28 28. 250 ml daily therefore need not be avoided, but the INR should be monitored closely 28. Further studies to clarify the possible interaction are still outstanding 29.

8. Overdosage, Tolerability, Limits

In controlled human studies, cranberry capsules of 500 mg twice daily as well as cranberry powder of 250 or 500 mg were tested over six months. One investigation in 176 participants – 120 with cranberry juice, 56 with placebo, median 168 days – reported mild adverse effects in 24.2 % of the cranberry group and 12.5 % of the placebo group (P =.07) (30). Another study recorded gastrointestinal complaints in 56 % under cranberry and 61 % under placebo (31).

Proven: A controlled study with 137 participants recorded 17 withdrawals (12 %), 6/69 (9 %) under cranberry and 11/68 (16 %) under trimethoprim (P = 0.205) (24). A review reported that adverse effects were common in all evaluated studies and that withdrawal rates were high in several studies (14). Further controlled human studies reported no serious adverse effects (7), no major adverse effects (33) and no adverse events (32). For children, the question of safety and recommended dose remains open (34).

9. The Most Robust Studies

Ordered by strength of evidence, not by familiarity: reviews and studies with many participants first. The complete evaluation comprises considerably more studies; the most robust are listed here.

Controlled Studies in Humans

• 1 Cranberry Reduces the Risk of Urinary Tract Infection Recurrence in Otherwise Healthy Women: A Systematic Review and Meta-Analysis (2017) — Review, 1.498 participants
• 2 Cranberry Juice, Cranberry Tablets, or Liquid Therapies for Urinary Tract Infection: A Systematic Review and Network Meta-analysis (2024) — Review, 3.091 participants
• 3 The effect of cranberry supplementation on Helicobacter pylori eradication in H. pylori positive subjects: a systematic review and meta-analysis of … (2022) — Review, 1.935 participants
• 4 Cranberry Supplements for Urinary Tract Infection Prophylaxis in Pregnant Women: A Systematic Review of Clinical Trials and Observational Studies on … (2023) — Review, 188 participants
• 5 The effects of cranberry on cardiovascular metabolic risk factors: A systematic review and meta-analysis (2020) — Review
• 6 Effects of blueberry and cranberry on type 2 diabetes parameters in individuals with or without diabetes: A systematic review and meta-analysis of … (2022) — Systematic review
• 7 Cranberry Extract for Symptoms of Acute, Uncomplicated Urinary Tract Infection: A Systematic Review (2020) — Systematic review
• 8 The Clinical Trial Outcomes of Cranberry, D-Mannose and NSAIDs in the Prevention or Management of Uncomplicated Urinary Tract Infections in Women: A … (2022) — Systematic review
• 9 The Effects of Cranberry Consumption on Glycemic and Lipid Profiles in Humans: A Systematic Review and Meta-Analysis of Randomized Controlled Trials (2024) — Systematic review
• 10 The effects of blueberry and cranberry supplementation on blood pressure in patients with cardiovascular diseases: A systematic review and … (2024) — Systematic review
• 11 The Effect of Cranberry Consumption on Blood Pressure: A Systematic Review and Meta-Analysis of Randomized Controlled Trials (2026) — Systematic review
• 12 The Effect of Cranberry Consumption on Body Weight and Liver Enzymes: A Systematic Review and Meta-Analysis of Randomized Controlled Trials (2026) — Systematic review
• 13 Cranberries for preventing urinary tract infections (2012) — 4.473 participants
• 14 Cranberries for preventing urinary tract infections (2008) — 1.049 participants
• 15 Effect of cranberry juice on eradication of Helicobacter pylori in patients treated with antibiotics and a proton pump inhibitor (2007) — 712 participants
• 16 Effectiveness of cranberry capsules to prevent urinary tract infections in vulnerable older persons: a double-blind randomized placebo-controlled … (2014) — 928 participants
• 17 Cranberries for preventing urinary tract infections (2023) — 8.857 participants
• 18 Cost-effectiveness of cranberry capsules to prevent urinary tract infection in long-term care facilities: economic evaluation with a randomized … (2014) — 928 participants
• 19 Cranberries for preventing urinary tract infections (2023) — 8.857 participants
• 20 Enteric-coated and highly standardized cranberry extract reduces antibiotic and nonsteroidal anti-inflammatory drug use for urinary tract infections … (2017) — 924 participants
• 21 Cranberries for preventing urinary tract infections (2013) — 4.473 participants
• 22 Methenamine Hippurate With Cranberry Capsules Versus Cranberry Alone for Urinary Tract Infection Prevention in a Short-Term Indwelling Foley Catheter … (2022) — 2.021.185 participants
• 23 Randomised trial of cranberry-lingonberry juice and Lactobacillus GG drink for the prevention of urinary tract infections in women (2001) — 150 participants
• 24 Cranberry or trimethoprim for the prevention of recurrent urinary tract infections? A randomized controlled trial in older women (2009) — 137 participants

10. Summary

As proven in humans, cranberry products can reduce the rate of recurrent urinary tract infections in women: The meta-analysis by Wang and colleagues across 13 randomised controlled trials with 1616 participants yielded a pooled risk ratio of 0,62 (95 %-KI 0,49–0,80), with more pronounced effects in female populations (RR 0,49; 95 %-KI 0,34–0,73). The Cochrane review by Jepson and Craig of 24 studies points in the same direction. For vascular function, inflammatory markers and the immune system, controlled human studies are available that show partly significant, but predominantly short-term changes.

Plausible is the anti-adhesive mechanism: Certain proanthocyanidins with A-type linkages inhibit the attachment of uropathogenic Escherichia coli to bladder epithelial cells, and this activity was detectable in urine samples after cranberry consumption. Hypothesis: The observed effects on the gut microbiota could contribute to the prevention of urinary tract infections via modulation of intestinal colonisation by uropathogenic pathogens. Both mechanisms of action have so far been described via surrogate parameters; controlled studies with clinical endpoints are still outstanding.

What would clarify the question is a long-term, blinded study in a sufficiently large population with clinical endpoints — such as the incidence of urinary tract infections or hard cardiovascular events — and a standardised product characterised for proanthocyanidins. Such a study would need to link anti-adhesive activity in urine, microbial composition and infection rates directly and record them over a longer period. Also still open is the optimal dosage; the Cochrane authors explicitly name it as unresolved. Comparability is hampered until then by the fact that composition varies considerably depending on variety, cultivation, processing and dosage form.

11. What Remains Open

• Dose and product standardisation: Which proanthocyanidin dose and which dosage form are required to achieve reproducible anti-adhesive activity in urine?
• Clinical Relevance of the Markers: Can the observed changes in vascular and metabolic markers be confirmed in large studies with hard endpoints?
• Delineation of Application Areas: In which patient groups is a benefit most likely, and where does the risk of delaying effective therapies predominate?

12. Further Paths

Topics, Modes of Action and Chains in Which This Substance Occurs — for All Who Wish to Look Beyond the Substance.

• Interaction Network