(See also Overview of Dietary Supplements.)
Cranberries are fruit that can be consumed whole or made into food products such as jellies and juices.
People most often take cranberries to help prevent and relieve the symptoms of UTIs. The effectiveness of cranberries in preventing UTIs has not been confirmed. Natural unprocessed cranberry juice contains anthocyanidins, 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.
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 mo, but that supplementation cannot treat UTIs (2, 3). However, a 2012 Cochrane review of 24 studies (4473 participants) has 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 (4). Standardization of cranberry products 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.
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.
Papas PN, Brusch CA, Ceresia GC. Cranberry juice in the treatment of urinary tract infections. Southwest Med 47(1):17-20, 1966.
Jepson RG, Craig JC. A systematic review of the evidence for cranberries and blueberries in UTI prevention. Mol Nutr Food Res 51(6): 738-745, 2007.
Stothers L. A randomized trial to evaluate effectiveness and cost effectiveness of naturopathic cranberry products as prophylaxis against urinary tract infection in women.Can J Urol 9(3):1558-1562, 2002.
Jepson RG, Williams G, Craig JC. Cranberries for preventing urinary tract infections. Cochrane Database Syst Rev 10:CD001321, 2012.