Cranberries — as cranberry juice, tablets or capsules — have been used for many years to prevent urinary tract infections (UTIs). They contain proanthocyanidins, substances that can prevent bacteria from sticking to the walls of the bladder. This may help prevent infections and reduce the need for working people to take time for medical appointments. However, there is currently no established regimen for what proanthocyanidins dose to use and no formal regulation by health authorities of cranberry products.
Cranberries contain proanthocyanidins, which inhibit the adherence of Escherichia coli to the urothelial cells lining the bladder. Image credit: David Mark.
Cranberries belong to a group of evergreen dwarf shrubs of the genus Vaccinium. In North America, cranberry refers to Vaccinium macrocarpon.
Cranberries comprise nearly 90% water, but they also contain various organic substances such as quinic acid, malic acid and citric acid as well as glucose and fructose.
Products made from cranberries include juice, syrup, jam, tablets and powder.
The active ingredient of cranberry is proanthocyanidin (PAC). Processing cranberries into various products such as tablets or capsules can reduce the PAC concentration so that some products may contain little or no PAC.
The belief that eating cranberries would be beneficial may have started centuries ago from the Native Americans who would eat cranberries as a remedy for UTIs and other illnesses.
Early studies attributed the antibacterial effects of cranberry to acidification of the urine by increasing the excretion of hippuric acid. Several studies, however, found no difference or only transient differences in the level of hippuric acid.
More recent research suggests that cranberries prevent bacteria — particularly Escherichia coli — from adhering to the uroepithelial cells lining the bladder wall.
Without adhesion, Escherichia coli cannot infect the mucosal surface of the urinary tract. In vitro, this adhesion is reduced by two components of cranberry: fructose and PACs.
“Our incredible result didn’t really surprise us, as we’re taught that when there’s more and better evidence, the truth will ultimately come out,” said first author Dr. Gabrielle Williams, a researcher at the Children’s Hospital at Westmead.
“UTIs are horrible and very common; about a third of women will experience one, as will many elderly people and also people with bladder issues from spinal cord injury or other conditions.”
“Even back in 1973, my mum was told to try cranberry juice to prevent her horrible and frequent UTIs, and for her it’s been a saviour. Despite me niggling in her ear about evidence, she’s continued to take it daily, first as the nasty sour juice and in recent years, the easy to swallow capsules. As soon as she stops, wham the symptoms are back. As usual, it turns out that mum was right! Cranberry products can help some women prevent UTIs.”
“If the UTI persists untreated it can move to the kidneys and cause pain and more complications, including sepsis in very severe cases, so prevention is the most effective way to reduce risks,” said Flinders University epidemiologist Dr. Jacqueline Stephens, co-author of the study.
“Most UTIs are effectively, and pretty quickly, treated with antibiotics, sometimes as little as one dose can cure the problem. Unfortunately, in some people UTIs keep coming back. Without being sure if or how it works, some healthcare providers began suggesting it to their patients.”
“It was a harmless, easy option at the time. Even centuries ago, Native Americans reportedly ate cranberries for bladder problems, leading somewhat more recently, to laboratory scientists exploring what it was in cranberries that helped and how it might work.”
In their review, the authors looked at 50 recent studies that included 8,857 randomised participants.
“The studies we looked at included a range of methods to determine the benefits of cranberry products,” Dr. Stephens said.
“The vast majority compared cranberry products with a placebo or no treatment for UTI and determined drinking cranberries as a juice or taking capsules reduced the number of UTIs in women with recurrent cases, in children and in people susceptible to UTI’s following medical interventions such as bladder radiotherapy.”
“It’s also important to consider that few people reported any side effects with the most common being tummy pain based on the results.”
“We also did not find enough information to determine if cranberry products are more or less effective compared with antibiotics or probiotics in preventing further UTIs.”
The data also don’t show any benefit for elderly people, pregnant women or in people with bladder emptying problems.
“The real benefits of cranberry products became clear when the researchers expanded the scope of the review to include the most recently available clinical data,” said senior author Professor Jonathan Craig, a researcher at Flinders University and the Children’s Hospital at Westmead.
“This is a review of the totality of the evidence and as new evidence emerges, new findings might occur.”
“In this case, the new evidence shows a very positive finding that cranberry juice can prevent UTI in susceptible people.”
“We have shown the efficacy of cranberry products for the treatment of UTIs using all the evidence published on this topic since the mid-nineties.”
“The earlier versions of this review didn’t have enough evidence to determine efficacy and subsequent clinical trials showed varied results, but in this updated review the volume of data has shown this new finding.”
“While cranberry products do help prevent UTIs in women with frequent recurrence, more studies are needed to further clarify who with UTI would benefit most from cranberry products,” the researchers concluded.
Their paper was published in the Cochrane Database of Systematic Reviews.
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G. Williams et al. 2023. Cranberries for preventing urinary tract infections. Cochrane Database of Systematic Reviews 4: CD001321; doi: 10.1002/14651858.CD001321.pub6
