Cranberry juice has long been recommended as a preventive for urinary tract infections, but research didn't always back that up. Finally, a new evidence helps support this well-worn advice. In a recent study (British Medical Journal, 2001, vol. 322, no. 1571), researchers placed 150 Finnish women with urinary tract infections into three groups. One group of women drank 50 ml of cranberry-lingonberry juice daily. A second group took a lactobacillus drink, and a third group had no intervention. After six months, only 16 percent of the women in the cranberry group suffered another UTI, compared with 39 percent in the lactobacillus group and 36 percent in the no-intervention group.

In the old days, experts surmised that cranberry worked by making urine more acidic and thereby resistant to bacterial growth. Today, researchers believe that cranberry contains substances that act as a sort of Teflon finish inside the urinary tract, preventing bacteria from adhering to the walls so that with every urination, bacteria are swept from the tract before they have an opportunity to multiply and produce infection.

Many health care practitioners will recommend cranberry juice or capsules when a urinary tract infection begins and for a month or so afterward to prevent reinfection while the bladder heals. So if you feel a UTI coming on—or want to ward off any new infections—go for the berries. Most experts recommend unsweetened cranberry juice because sugar feeds rather than treats infection. If the taste is too bitter, sweeten it with stevia, suggests Atlanta-based Maureen Melendez, ND.

The amount of juice you consume is important, too. About 16 ounces a day is a general rule of thumb. When drinking juice is not practical or desirable, equivalent amounts of encapsulated dried berries are effective: Try one pill twice a day. In a pinch, cranberry juice cocktail, although sugary, does contain 10 percent to 20 percent cranberry, and for some individuals, drinking two to three glasses of that a day may do the trick.