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People most often take cranberries to help prevent and relieve the symptoms of urinary tract infections (UTIs). The effectiveness of cranberries in preventing UTIs has not been confirmed. Natural unprocessed cranberry juice contains anthocyanidins (eg, proanthocyanidin), which prevent Escherichia coli from attaching to the urinary tract wall.

Some people take cranberry juice to reduce fever and treat certain cancers; however, there is no scientific proof that it is effective for these uses.

The US Food and Drug Administration (FDA) has stated that it authorized (allowed) qualified health claims for a reduced risk of recurrent UTIs in healthy women (see FDA Announces Qualified Health Claim for Certain Cranberry Products and Urinary Tract Infections).

In 1966, the first clinical trial, uncontrolled, evaluating the positive effects of cranberry juice in preventing UTIs was published (1). Since that time numerous trials have been performed evaluating different populations, severity of medical conditions, dosages, time, and form of supplement in juice or extract capsule/tablet.

The majority of evidence suggests that cranberry juice or extract can have a small, yet significant effect on preventing the recurrence of UTIs over 12 months, but that supplementation cannot treat UTIs (2). However, a 2012 Cochrane review of 24 studies (4473 participants) placed some doubt on the effectiveness of the supplement, indicating a small trend toward fewer UTIs with supplementation, but that the finding was not statistically significant (3). A 2017 meta-analysis of 28 studies (4947 participants) found that UTIs are decreased significantly by 33% (4). A different meta-analysis of randomized controlled trials in women at risk for UTIs also found that cranberry reduced UTI risk by 26% (5).

Standardization of cranberry products and specifying proanthocyanidin (PAC) content may help to clarify results and resolve the discrepancy. Physiologic differences in the urinary tract and proper hygiene of female individuals studied also could contribute to the variability in response. Due to concern for antibiotic resistance, the American Urological Association 2019 guidelines in women with recurrent UTIs has stated that clinicians may offer cranberry prophylaxis, although this is a Grade C evidence level recommendation (6).

No adverse effects are known. However, because most cranberry juice is highly sweetened to offset its tart taste, people with diabetes should not consume cranberry juice unless it is artificially sweetened. Because cranberry increases urinary acidity, it may promote stone formation in patients with uric acid kidney stones.

Cranberry products may increase the effects of warfarin. Cranberry may increase the effect of the statin atorvastatin and the antihypertensive nifedipine.

1. 1. Papas PN, Brusch CA, Ceresia GC: Cranberry juice in the treatment of urinary tract infections. Southwest Med 47(1):17-20, 1966. PMID: 5900988

2. 2. Jepson RG, Craig JC: A systematic review of the evidence for cranberries and blueberries in urinary tract infection prevention. Mol Nutr Food Res 51(6): 738-745, 2007. doi: 10.1002/mnfr.200600275

3. 3. Jepson RG, Williams G, Craig JC: Cranberries for preventing urinary tract infections. Cochrane Database Syst Rev 10:CD001321, 2012. doi: 10.1002/14651858.CD001321.pub5

4. 4. Luís Â, Domingues F, Pereira L: Can cranberries contribute to reduce the incidence of urinary tract infections? A systematic review with meta-analysis and trial sequential analysis of clinical trials. J Urol 198(3):614-621, 2017. doi: 10.1016/j.juro.2017.03.078

5. 5. Fu Z, Liska D, Talan D, et al: Cranberry reduces the risk of urinary tract infection recurrence in otherwise healthy women: a systematic review and meta-analysis. J Nutr 147(12):2282-2288, 2017. doi: 10.3945/jn.117.254961

6. 6. Anger J, Lee U, Ackerman AL, et al: Recurrent uncomplicated urinary tract infections in women; AUA/CUA/SUFU guideline. J Urol 202(2):282-289, 2019. doi: 10.1097/JU.0000000000000296

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

1. National Institutes of Health (NIH), National Center for Complementary and Integrative Health: General information on the use of cranberry as a dietary supplement