The active ingredients in cranberries prevent bacteria from adhering to the bladder wall.
A urinary tract infection (UTI) can affect any part of the urinary system, kidneys, bladder or urethra.
More than 3 million Americans, mostly women, experience a UTI every year.
Symptoms include frequent, painful urination, pelvic pain and traces blood in the urine. The infection does not normally last long, and most patients self-diagnose.
For many, the first port of call is a box of cranberry juice. However, new research suggests that while cranberry capsules can help, cranberry juice may be little more than a panacea.
Dr. Timothy Boone, PhD, vice dean of the Texas A&M Health Science Center College of Medicine in Houston, and colleagues wanted to know if cranberries can really help.
Cranberry capsules reduce the prevalence of UTI
The team studied 160 patients aged 23-88 years who were undergoing elective gynecological surgery between 2011-2013. Normally, 10-64% of women undergoing this kind of surgery will develop a UTI following the removal of the catheter.
Half of the patients received two cranberry juice capsules twice daily - the equivalent in strength to two 8-ounce servings of cranberry juice - for 6 weeks after surgery. The others took a placebo.
Cranberry capsules lowered the risk of UTIs by 50%. In the cranberry treatment group, 19% of patients developed a UTI, compared with 38% of the placebo group.
So, how does it work? For a UTI to occur, bacteria must adhere to and invade the lining of the bladder. Cranberries contain A-type proanthocyanidins (PACs), which interfere with the bacteria's ability to the bladder wall, reducing the likelihood of infection.
Cranberry juice will not do the trick
However, the researchers point out that since a cranberry capsule provides the equivalent of 8 ounces of cranberry juice, a patient would need a lot of pure cranberry to prevent an infection.
Dr. Boone explains: "It takes an extremely large concentration of cranberry to prevent bacterial adhesion. This amount of concentration is not found in the juices we drink. There's a possibility it was stronger back in our grandparents' day, but definitely not in modern times."
"Cranberry juice, especially the juice concentrates you find at the grocery store, will not treat a UTI or bladder infection. It can offer more hydration and possibly wash bacteria from your body more effectively, but the active ingredient in cranberry is long gone by the time it reaches your bladder."
He also cautions that a UTI and an overactive bladder may show similar symptoms, and people should seek medical advice if any adverse symptoms appear, to prevent UTIs from developing into kidney infections.
Treatment of UTIs can be complicated. Approximately 20-30% of women have recurring UTIs, and concerns about antibiotic resistance mean that both doctors and patients may be unwilling to use such medication.
As a result, the researchers propose using probiotics as a safe alternative to antibiotics in the treatment of UTIs. Probiotics are "good" bacteria found in the digestive tract and naturally occurring in certain foods, such as fermented vegetables - including sauerkraut and kimchi - and live-cultured yogurt.
Dr. Boone points out that there are many benefits of probiotics, although more research is still needed.
Our Knowledge Center article features more information about the health benefits of cranberries.
Medical News Today has previously reported on research suggesting that painkillers may help to prevent UTIs.