Do Cranberries Prevent Urinary Tract Infections?
Urinary tract infections (UTI) affect up to 60% of women over the course of their lifetime. These infections result in bothersome symptoms including frequent, painful urination, they lead millions of people to seek medical care and they cost billions of healthcare dollars each year. Is it any wonder then that we would hope to find some way to prevent recurrence of these infections? For many, that hope has been placed in the tart little berry that makes its appearance each Thanksgiving. But how effective are cranberries at preventing infection? What about all of the cranberry extracts that we see? As with so many aspects of medicine, the answers may not always be as simple as we would like.
First, let’s talk about cranberry juice. Early on, several studies indicated that cranberry juice was effective in preventing recurrence of urinary tract infections. A class of chemicals called proanthocyanidins (PAC) found in cranberries are thought to keep E. coli (the most common cause of urinary tract infections) from binding to bladder cells. It seemed to make sense that drinking cranberry juice would prevent infections from recurring. However, PAC breaks down after 10-12 hours meaning people would need to drink cranberry juice twice daily to maximize the benefit. Furthermore, many studies show a lot of people just don’t like the tart taste of cranberry juice and stop drinking it (sorry, the sugar-sweetened 10% juice cocktail won’t cut it here). Finally, as more and more studies have been done, fewer of them have shown a benefit and, overall, the evidence for cranberry juice has been questioned. When taken as a whole, it seems more likely that cranberry juice doesn’t make much of a difference in preventing infections.
What about cranberry extracts? There are studies that show benefits from capsules containing extracted PAC, especially in certain populations that are at high risk of getting new infections. Unfortunately, these extracts suffer from a lack of standard make-up. By that, I mean that the amount of PAC from one supplement to another varies greatly. For example, one study found that the amount of PAC across 7 different cranberry extracts varied by 30 times. So, one brand of extract contained 30 times the amount of PAC compared with another. With so much variability, it is very difficult to know whether these capsules can prevent infections. So, again, when we look at all of the studies together, it seems less likely that there is much of an effect.
What to do? Well, there are studies ongoing for both cranberry juice and cranberry extract supplements that may find particular doses are effective or that certain types of people may benefit, so stay tuned. There are other compounds such as d-mannose sugar that may prove to be useful as well. Women with recurrent urinary tract infections may benefit from a medical evaluation to see if there is an underlying urologic problem that may be causing recurrent infections. I often find in my practice issues such as complications from previous surgeries that can explain recurrent infections. It may even be that our over-use of antibiotics may precipitate infections by killing of normal, beneficial vaginal bacteria. There is at least some evidence that probiotics (essential doses of healthy bacteria) may provide benefit, though these studies are ongoing.
Colin M. Goudelocke, M.D.