Many women suffer from frequent bladder infections (also called cystitis), which are the most common type of urinary tract infection (UTI). Such infections are among the leading causes of physician visits in the U.S., usually resulting in the prescription of antibiotics.
Women are more susceptible to UTIs because their urethral opening is closer to the anus, where bacteria thrive, and because the female urethra is much shorter than a man’s, allowing bacteria easier access to the bladder. A small percentage of men do get UTIs, usually at older ages.
It’s no wonder that many women wonder if there’s any truth to longstanding claims that cranberry juice (or capsules of cranberry extract) can help prevent recurring infections. It has been hypothesized that compounds called proanthocyanidins in cranberries may help prevent bladder infections by keeping E. coli and other bacteria from sticking to the lining of the bladder, as well as by having anti-inflammatory effects.
But research has produced conflicting results, in part because studies have used different amounts and types of cranberry products, involved different populations, and often had methodological shortcomings, such as not using objective or consistent criteria to identify UTIs.
A look at the research
Studies sponsored by Ocean Spray—which has spent millions on research on cranberries for UTIs and has even sought FDA approval for a UTI health claim on its labels—have been more likely to yield positive results than independent studies. However, the studies used UTI symptoms as criteria, not confirmed diagnoses.
In 2012, the most recent review by the well-regarded Cochrane Collaboration looked at 24 studies and concluded that the evidence does not support the use of cranberry products for UTI prevention. Since then, one of the better studies with positive results was a large clinical trial in the American Journal of Clinical Nutrition in 2016. It was funded by Ocean Spray, and two of the six researchers were its employees.
It involved 373 women (average age 41) with a history of a recent UTI who were randomly assigned either a daily glass of cranberry juice drink for 24 weeks or a placebo that looked and tasted similar. During this time there were 39 UTIs in the cranberry group and 67 in the placebo group, based on symptoms—a 40 percent reduction. The cranberry drink contained diluted juice concentrate, sugar, and sugar substitutes, with 35 calories per cup. (Unsweetened cranberry juice is very tart, and regular sugar-sweetened versions contain about 140 calories per cup.)
In contrast, a rigorous NIH-funded clinical trial in the Journal of the American Medical Association in 2016 did not find benefits from cranberry in older women living in nursing homes, who tend to have high rates of urinary tract infections. Compared to a placebo, standardized cranberry capsules (containing proanthocyanidins), taken for a year, did not reduce bacteria in urine, pyuria (white blood cells in urine, a sign of infection), or symptomatic UTIs. According to the accompanying editorial, the evidence from well-designed research, supported by this study, “is convincing that cranberry products should not be recommended as a medical intervention for the prevention of UTI.”
Bottom line: If one of my patients or a Wellness Letter reader asked me about cranberries as a preventive for bladder infections or other UTIs, I’d tell her that it’s still unclear if cranberry juice or extracts can help, but it probably can’t hurt to try them. I’d also tell her to drink at least six to eight cups of water a day. As we reported earlier this year, a 2018 study confirmed that this is one good way to reduce the recurrence of bladder infections.
This article first appeared in the UC Berkeley Wellness Letter.
Also see What's Making Your Urine Smell?