Can cranberries prevent bladder infections?

Philip J. Goscienski, M.D.

October 2011

The colorful cranberry was one of the first plant foods that Native Americans introduced to struggling European colonists in the early 1600s. The Pilgrims incorporated cranberries into their Thanksgiving feasts, where they have retained a prominent position ever since.

Bladder infections are one form of urinary tract infection (UTI) that most women are unfortunately very familiar with, often starting in early childhood. For several decades various authorities have recommended cranberry juice as a measure to ward off these annoying and sometimes serious infections. Studies during this period have shown conflicting results. Several analyses show that cranberry juice has an effectiveness of about 35 percent but others are not so conclusive. There are no studies that show that cranberry juice or cranberry concentrates can cure an infection.

Laboratory studies seem to indicate a plausible mechanism to explain why cranberry juice does work in preventing some bladder infections. The most common agent is the familiar E. coli bacterium, a microorganism that makes up a substantial part of the population of germs that reside in the large intestine. Some strains are equipped with hair-like projections call fimbriae that the bacteria use to attach to the lining of the bladder. Certain ingredients in cranberry juice interfere with the attachment process but only among those strains of E coli that possess fimbriae. Non-fimbriated strains get a pass.

Cranberry products aren't all alike, either. There are differences among strains and even more variation among juice products. Some research trials have failed because the participants could not maintain a consistent intake of up to a quart a day of pucker-producing cranberry juice. No great surprise there.

There is no sure way to prevent all bladder infections but there are some measures that help. Even though cranberry juice has limited effectiveness it makes sense to drink it several times a week — until you really get tired of it. Avoid a concentrated urine by taking plenty of liquids. That means more trips to the bathroom but it also means you'll have a lower likelihood of developing kidney stones — a malady that is a lot more painful than a bladder infection. Some women, especially those who have borne several children, may not be able to empty the bladder completely, a condition that fosters infection. Modern ultrasound technology makes it possible to diagnose that problem quickly and with no discomfort. Medical specialists can offer more options if these fail.

Philip J. Goscienski, M.D. is the author of Health Secrets of the Stone Age, Better Life Publishers 2005. Contact him at