In test tube studies, cranberry prevents E. coli, the most common bacterial cause of UTIs, from adhering to the cells lining the wall of the bladder. This anti-adherence action is thought to reduce the ability of the bacteria to cause a UTI.^{1, 2} The proanthocyanidins in the berry have exhibited this anti-adherence action.³ Cranberry has been shown to reduce bacteria levels in the urinary bladders of older women significantly better than placebo, an action that may help to prevent UTIs.⁴ A small double-blind trial with younger women ages 18–45 years with a history of recurrent urinary tract infections, found that daily treatment with an encapsulated cranberry concentrate (400 mg twice per day) for three months significantly reduced the recurrence of urinary tract infections compared to women taking a placebo.⁵ Other preliminary trials in humans suggest cranberry may help people with urostomies and enterocystoplasties to keep their urine clear of mucus buildup and possibly reduce the risk of UTIs.⁶ However, one trial found that cranberry did not reduce the risk of UTIs in children with neurogenic bladder disease (a condition that does not allow for proper flow of urine from the bladder) who were receiving daily catheterization.⁷