A systematic review of the evidence for cranberries and blueberries in UTI prevention Mol Nutr Food Res. 2007 Jun;51(6):738-45. doi: 10.1002/mnfr.200600275. Ruth G Jepson
In this review we assess the effectiveness of cranberry and blueberry products in preventing symptomatic urinary tract infections (UTIs). …No relevant trials of blueberry products were identified. …There is some evidence from four good quality RCTs that cranberry juice may decrease the number of symptomatic UTIs over a 12-month period, particularly in women with recurrent UTIs.