Harvard Women's Health Watch

Does cranberry extract prevent UTIs?

Ask the doctor

Q. I recently read that cranberry capsules don’t prevent urinary tract infections (UTIs). I’ve been taking them for several years and seem to be having UTIs less frequently. Should I stop?

A. You might be referring to a clinical trial reported in The Journal of the American Medical Association recently. That study, conducted in a nursing home, found that cranberry-extract capsules didn’t prevent UTIs in women who were prone to them. Although the women in this study had an average age of 87, earlier trials in college students and middle-aged women have had similar results.

Cranberry juice has been a popular remedy for UTIs for almost a century. The rationale for using cranberry juice and cranberry capsules is that they increase the acidity of urine, which presumably makes it more difficult for harmful E. coli bacteria to get a foothold in the urinary tract. Yet this effect hasn’t been demonstrated in humans.

There is certainly no evidence that cranberry capsules are harmful, but it’s unlikely that they will prevent UTIs. If you’re not bothered by UTIs, there isn’t good reason to believe that taking cranberry extract has been protecting you. If your UTIs resume, you should talk to your clinician. Other approaches, particularly antibiotics, have proved to be more effective.

That doesn’t mean you still shouldn’t enjoy cranberries—which are a good source of vitamin C and fiber—if you like their flavor. You may want to combine fresh or frozen cranberries with oranges or apples to ease the tartness. Try to avoid processed cranberry products, which often contain added sugars or artificial sweeteners.

— by Hope Ricciotti, M.D., and Hye-Chun Hur, M.D., M.P.H.

Editors in Chief, Harvard Women’s Health Watch

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