Cranberry is an evergreen shrub that is grown in North America and Europe. The processed fruit and juice, both rich in vitamin C, are widely consumed as food. The juice extract is marketed as a dietary supplement for urinary tract health and to prevent urinary tract infections (UTIs). It has also been used for oral and gastrointestinal infections, cardiovascular diseases, and to protect against cancer. In preclinical studies, cranberry juice extracts and constituents exhibited antibacterial ⁽¹⁾, antimicrobial ⁽⁴⁵⁾, antifungal ⁽⁴⁶⁾, anti-inflammatory ⁽⁴⁷⁾, antioxidant ⁽⁴⁸⁾, and antiadherence ⁽⁴⁹⁾ properties.

Studies on whether cranberry products can prevent UTIs have been conducted in various populations, but results are mixed. Cranberry extracts can help prevent UTIs in adults ^(2) (3), children ⁽⁴⁾, prostate cancer patients undergoing radiation therapy ^(5) (50), and patients following urostomy ⁽⁶⁸⁾. In women undergoing pelvic floor surgery, cranberry prophylaxis had no beneficial effects against UTIs, although UTI prevalence overall was lower than expected ⁽⁷²⁾. A large double-blind study of older adults with high-baseline UTI risk showed benefit ⁽⁵¹⁾, but another similar study reported negative findings ⁽⁵²⁾. A subsequent analysis revealed increased costs with no meaningful reduction in UTI rates in a geriatric nursing home environment ⁽⁵³⁾. Studies of cranberry juice for recurrent UTIs have also been mixed, with one study finding no benefit among college-aged women ⁽⁶⁾, and another observing significant reductions in UTI relapse in women over age 50 ⁽⁵⁴⁾. Cranberry was not as effective or cost-effective as trimethoprim-sulfamethoxazole in preventing UTIs in premenopausal women, but patients were less likely to develop antibiotic-resistant bacteria ^(8) (55). In volunteers from different regions, anti-adhesion activity with cranberry powder was found to be dose-dependent ⁽⁷⁾. Overall, a systematic review determined that cranberry juice was more effective than capsules or tablets  ⁽⁵⁶⁾, but despite some support for recurrent UTI prophylaxis ⁽⁶⁹⁾, there is not enough evidence to recommend cranberry juice for UTI prevention ^(9) (70).

In other studies, cranberry juice inhibited adhesion of H. pylori to human gastric mucosa ⁽¹⁸⁾, and regular consumption may suppress H. pylori infection ^(19) (20), a major factor in peptic ulcer disease and gastric cancer. When used with standard treatment, cranberry juice helped eradicate H. pylori ⁽²¹⁾. It potential to prevent plaque formation and gum disease as well may be due to its anticolonizing and antiadhesion properties ^(22) (23).

Preclinical studies suggest antiproliferative effects against prostate ^{(10) (11) (12)}, liver ⁽¹³⁾, lung ⁽⁵⁷⁾, neuroblastoma ⁽⁵⁸⁾, breast ⁽¹⁴⁾, ovarian ⁽¹⁵⁾, gastric ⁽⁵⁹⁾, colon ^(12) (16), esophageal ⁽⁶⁰⁾, and oral ⁽¹²⁾ cancer cells with cranberry extracts and proanthocyanidins. In humans however, cranberry juice did not lower oxidative status, suggesting a lack of protective effect against cancer or heart disease ⁽¹⁷⁾.

Cranberry juice has high concentrations of oxalates, and should be avoided in patients at risk for kidney stones  ^(40) (73). Other data suggest it may be helpful in uncommon forms including struvite stones, which are associated with bladder infections ^{(33) (62) (63)}.