• Minimum dose of cranberry-containing product necessary to achieve a 30% prophylaxis of UTIs in women with recurrent UTIs
  
• Whether the degree of UTI prophylaxis is related to the dose of cranberry-containing product (dose response curve)
  
• Whether proanthocyanidin concentration in the urine correlates with UTI prophylaxis
  

Although cranberry-containing products are commonly taken to prevent UTIs and other urinary symptoms, an optimally effective dose has not been established, and the chemicals responsible for the UTI-preventing properties in cranberry-containing products have yet to be determined. This study will determine the minimum dose of cranberry-containing product necessary to prevent UTIs, the effectiveness of cranberry-containing products in fighting different strains of E. coli, and the long-term effects of cranberry-containing product consumption. This study will also determine whether plant pigments called proanthocyanidins influence the UTI-preventing properties of cranberry-containing products.

This study will last 2 years. Participants will be randomly assigned to receive varying doses of either cranberry-containing products or placebo for 1 year. Some participants will receive cranberry or placebo supplement tablets; others will receive cranberry juice or a placebo beverage. Clinic visits will occur every 2 months; urine collection will occur at each visit. Some participants will be asked to collect 24-hour urine samples every 8 weeks and provide urine samples on Days 1, 3, 5 and 7.

Laboratory tests will be used to assess participants during the study. A 3-day course of antibiotics will be provided to participants developing a UTI during the course of the study. Telephone interview follow-up at 6 and 12 months after the study will determine whether cranberry-containing product use has continued and whether UTIs have recurred.