Cranberries and cranberry juice have been long used to ward off UTIs, however, it is unclear how exactly they prevent infection. One theory suggests, certain sugars and flavanol compounds, present in cranberries, deter bacteria from sticking to cells that line the urinary tract.
Researchers examined data from 24 studies that included a total of 4,473 people. The treatment groups were given cranberry juice, capsules or tablets, and those in control groups had placebo cranberry products, methenamine hippurate, antibiotics, lactobacillus, water, or nothing.
The authors pointed out that the results show that cranberry juice is significantly less beneficial than previous research has stated.