Cranberries vs. Antibiotics for Bladder Infections
Study Shows Antibiotics Work Best, but Experts Won't Dismiss Cranberries Just Yet
Doses, Study Design Questioned
Other experts say that the research has some limits that prevent it from being able to settle any questions about the effectiveness of cranberries for UTIs.
The first is that the study didn't include a comparison group of women who weren't getting any prevention at all. Comparison groups are important to give an idea of the magnitude of effect that an intervention might be having.
The second is that while women who were taking the antibiotics reported having fewer UTIs than the cranberry group did, the number of infections confirmed by laboratory testing was not statistically different between the two groups.
The third was that the cranberry capsules used in the study had relatively small amounts of active ingredients in them. "The dose of the cranberry that they used in that particular study was way too low," says Bill J. Gurley, PhD, a professor in the department of pharmaceutical sciences at the University of Arkansas for Medical Sciences, in Little Rock.
Gurley says a government-sponsored study is under way that may shed more light on how much cranberry is needed to prevent infections.
Other studies have found that when cranberry extract is used in higher doses, about eight times as high as were used in this study, they do appear to keep bacteria from sticking together in the bladder, which may help prevent an infection.
"The studies that have been well-designed, and there have been a handful that were well-designed," have shown that cranberries can be effective, says Amy B. Howell, PhD, an associate research scientist at the Marucci Center for Cranberry and Blueberry Research at Rutgers University in New Brunswick, N.J.
"If the bacteria can't bind to the bladder wall, they will not inject their toxins and grow and cause an infection, they just get washed out in the urine stream," says Howell.
"The key here, which has relevance to this latest study, is that you're not killing the bacteria. You're not building up these populations of resistant bacteria," which should keep them sensitive to antibiotics in case an infection does take hold, she says.