Has your mother ever recommended cranberry juice for a urinary tract infection (UTI)? Mine sure has (and for any other ailments that aren't cured by Vitamin E)! Researchers hypothesize that cranberries can prevent UTIs by selecting against bacterial strains in the stool that are more likely to adhere to the urogenital tract and cause a UTI. In other words, it favors the good bacteria that don't cause UTIs. Another theory is that cranberry prevents E.coli bacteria from adhering to the cells that line the urogenital tract. Yet another theory is that it affects the tiny bacterial components that allow UTI-causing bacteria to attach to our cells.
Dr. Foxman and her colleagues at the University of Michigan Ann Arbor conducted a randomized, controlled trial to learn whether cranberry pills are effective at preventing UTIs in a high risk group of women. The most common side effect of pelvic floor surgery is UTI. In fact, in the six weeks following catheter removal after elective urogenital surgery, 10-64% of women will develop a symptomatic UTI. In the general population, only 3-4% of women will develop a UTI over a six week period (although that's still quite a lot of UTIs).
The researchers enrolled 160 women undergoing elective benign gynecologic surgery that required catheterization, excluding fistula repair and vaginal mesh removal. Half of the women took two cranberry pills a day for six weeks after surgery, equivalent to drinking two eight-ounce glasses of delicious cranberry juice. The other half of the women took two placebo pills a day. The pills all looked identical so women didn't know if they were taking cranberry pills or fake pills.
The results showed that 19% of the women taking the cranberry pills and 38% of the women taking fake pills were diagnosed with the clinical symptoms of UTI and given treatment. That's pretty impressive- taking the cranberry pills cut the UTI rate in half. You may wonder: were these all real UTIs? How do we know if the doctors didn't do a urine culture? The study authors were able to obtain culture data on some of the UTIs. The percentage of UTIs that were confirmed by culture was similar in both groups, 77% and 80%. Going one step further, when the study authors compared the two groups using only UTIs that were confirmed by culture, the results remained the same. The cranberry group still had significantly fewer UTIs than the placebo group. Most importantly, there was no difference in the incidence of side effects between the cranberry and placebo groups, suggesting that the cranberry supplements were safe to take.
There is a long history of research on cranberry juice and supplements in treating and preventing UTIs. This study supports the use of cranberry supplements in a group of women at high risk for UTIs. Given the relatively low risk and cost, we may see doctors start to recommend this, but of course, further studies with more patients will likely follow to corroborate the evidence.