Una revisione sistematica della letteratura conferma il mirtillo rosso un rimedio efficace per le infezioni ricorrenti delle vie urinarie

16 Maggio, 2023

L’uso del mirtillo rosso (cranberry) come rimedio per le infezioni delle vie urinarie è radicato nella medicina tradizionale, soprattutto in Nordamerica. L’analisi puntuale degli studi di intervento condotti fino a un decennio fa non ha però permesso di confermarne l’efficacia terapeutica nei confronti di una serie di disturbi di origine prevalentemente batterica, che interessano mediamente il 30% della popolazione femminile, oltre ad alcune categorie fragili, come i pazienti oncologici in chemio e radioterapia. Dalla revisione sistematica della letteratura pubblicata nel 2012 è infatti emersa una sostanziale neutralità del mirtillo rosso sulle infezioni delle vie urinarie.

Giunge invece a una diversa conclusione una nuova review sistematica che, grazie all’aggiornamento della letteratura degli ultimi anni, comprende un numero doppio di studi di intervento, per un totale di circa 9000 soggetti, dimostrando che succhi e integratori a base di mirtillo rosso sono efficaci specificamente nel ridurre le infezioni delle vie urinarie ricorrenti, sintomatiche e confermate dall’esame delle urine, in assenza di effetti indesiderati rilevanti anche in caso di assunzione prolungata.

Il meccanismo d’azione sembra essere legato alla presenza delle proantocianidine, sostanze di natura polifenolica contenute ad alti livelli nei mirtilli rossi (e quindi nei succhi e negli integratori derivati), che inibiscono l’adesione alle cellule che rivestono la vescica di Escherichia coli, uno dei batteri maggiormente responsabili di questo tipo di infezioni. Con ricadute potenzialmente favorevoli in termini sia di miglioramento della qualità della vita delle persone e sia di salute pubblica, come sottolineano gli Autori dello studio nelle conclusioni.

Cranberries for preventing urinary tract infections

Williams G, Hahn D, Stephens JH, Craig JC, Hodson EM.
Cochrane Database Syst Rev. 2023 Apr 17;4(4):CD001321. doi: 10.1002/14651858.CD001321.pub6.

BACKGROUND: Cranberries contain proanthocyanidins (PACs), which inhibit the adherence of p-fimbriated Escherichia coli to the urothelial cells lining the bladder. Cranberry products have been used widely for several decades to prevent urinary tract infections (UTIs). This is the fifth update of a review first published in 1998 and updated in 2003, 2004, 2008, and 2012.
OBJECTIVES: To assess the effectiveness of cranberry products in preventing UTIs in susceptible populations.
SEARCH METHODS: We searched the Cochrane Kidney and Transplant Specialised Register up to 13 March 2023 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register Search Portal (ICTRP) and ClinicalTrials.gov.
SELECTION CRITERIA: All randomised controlled trials (RCTs) or quasi-RCTs of cranberry products compared with placebo, no specific treatment or other intervention (antibiotics, probiotics) for the prevention of UTIs were included.
DATA COLLECTION AND ANALYSIS: Two authors independently assessed and extracted data. Information was collected on methods, participants, interventions and outcomes (incidence of symptomatic UTIs, positive culture results, side effects, adherence to therapy). Risk ratios (RR) with 95% confidence intervals (CI) were calculated where appropriate. Study quality was assessed using the Cochrane risk of bias assessment tool. Confidence in the evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.
MAIN RESULTS: For this update 26 new studies were added, bringing the total number of included studies to 50 (8857 randomised participants). The risk of bias for sequence generation and allocation concealment was low for 29 and 28 studies, respectively. Thirty-six studies were at low risk of performance bias, and 23 studies were at low risk of detection bias. Twenty-seven, 41, and 17 studies were at low risk of attrition bias, reporting bias and other bias, respectively. Forty-five studies compared cranberry products with placebo or no specific treatment in six different groups of participants. Twenty-six of these 45 studies could be meta-analysed for the outcome of symptomatic, culture-verified UTIs. In moderate certainty evidence, cranberry products reduced the risk of UTIs (6211 participants: RR 0.70, 95% CI 0.58 to 0.84; I² = 69%). When studies were divided into groups according to the treatment indication, cranberry products probably reduced the risk of symptomatic, culture-verified UTIs in women with recurrent UTIs (8 studies, 1555 participants: RR 0.74, 95% CI 0.55 to 0.99; I² = 54%), in children (5 studies, 504 participants: RR 0.46, 95% CI 0.32 to 0.68; I² = 21%) and in people with a susceptibility to UTIs due to an intervention (6 studies, 1434 participants: RR 0.47, 95% CI 0.37 to 0.61; I² = 0%). However, in low certainty evidence, there may be little or no benefit in elderly institutionalised men and women (3 studies, 1489 participants: RR 0.93, 95% CI 0.67 to 1.30; I² = 9%), pregnant women (3 studies, 765 participants: RR 1.06, 95% CI 0.75 to 1.50; I² = 3%), or adults with neuromuscular bladder dysfunction with incomplete bladder emptying (3 studies, 464 participants: RR 0.97, 95% CI 0.78 to 1.19; I² = 0%). Other comparisons were cranberry products with probiotics (three studies) or antibiotics (six studies), cranberry tablets with cranberry liquid (one study), and different doses of PACs (two studies). Compared to antibiotics, cranberry products may make little or no difference to the risk of symptomatic, culture-verified UTIs (2 studies, 385 participants: RR 1.03, 95% CI 0.80 to 1.33; I² = 0%) or the risk of clinical symptoms without culture (2 studies, 336 participants: RR 1.30, 95% CI 0.79 to 2.14; I² = 68%). Compared to probiotics, cranberry products may reduce the risk of symptomatic, culture-verified UTIs (3 studies, 215 participants: RR 0.39, 95% CI 0.27 to 0.56; I = 0%). It is unclear whether efficacy differs between cranberry juice and tablets or between different doses of PACs as the certainty of the evidence was very low. The number of participants with gastrointestinal side effects probably does not differ between those taking cranberry products and those receiving placebo or no specific treatment (10 studies, 2166 participants: RR 1.33, 95% CI 1.00 to 1.77; I² = 0%; moderate certainty evidence). There was no clear relationship between compliance with therapy and the risk for repeat UTIs. No difference in the risk for UTIs could be demonstrated between low, moderate and high doses of PACs.
AUTHORS’ CONCLUSIONS: This update adds a further 26 studies taking the total number of studies to 50 with 8857 participants. These data support the use of cranberry products to reduce the risk of symptomatic, culture-verified UTIs in women with recurrent UTIs, in children, and in people susceptible to UTIs following interventions. The evidence currently available does not support its use in the elderly, patients with bladder emptying problems, or pregnant women.

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