Cranberries may help prevent bladder and urinary tract infections and, importantly, reduce the need for working people to take time for medical appointments
Cranberries are a superfood. They are extremely high in antioxidants and may help prevent heart disease and cancers. Their heath benefits were well known to the First Peoples of North America, who consumed cranberries for an assortment of medicinal purposes: as ‘blood purifiers’, as a laxative, for treating fever, stomach cramps, a slew of childbirth-related injuries, and bladder problems. Eventually, even non-native people came to view cranberries as helping to prevent urinary tract infections (UTIs) in susceptible women. But is this idea merely wishful thinking, or is it really true?
What is the secret of cranberries’ anti-UTI magic?
In the 1980s and 1990s (i. e.; ref & ref), scientists began to explore what makes cranberries so beneficial. They discovered that cranberries, Vaccinium macrocarpon, a native fruit of North America, have high concentrations of proanthocyanidins (ref). Proanthocyanidins are a class of polyphenols that are natural pigments, providing red, blue or purple colors to the the fruit or flowers of many plants. Cranberries rely on proanthocyanidins to protect the plant and its fruits from attack by microbes. In people, proanthocyanidins appear to also have anti-microbial properties: they prevent the most common UTI-causing bacteria from sticking to the bladder wall and causing infection.
Are cranberries equally helpful to all people? Faced with a lack of scientific evidence for precisely how or for whom cranberries are most helpful, healthcare providers didn’t know who might benefit most from them. A newly published review of the literature set out to find some answers. A team of Australian scientists, led by epidemiologist Gabrielle Williams, a Senior Lecturer in Public Health at the University of Sydney, reviewed 50 previously published randomized controlled trials involving 8857 people and found that taking cranberry juice, tablets or capsules really do reduce the risk of UTIs by more than 25% in women, by 50% in children, and by 53% in people who are susceptible to UTIs following medical interventions, such as bladder radiotherapy.
Dr Williams and her collaborators also analyzed randomized controlled trials that compared occurrence of UTIs in people taking a cranberry product to those receiving other treatments, such as antibiotics or probiotics. Unfortunately, the researchers did not find enough information to determine whether cranberries and their products are more or less effective compared with antibiotics or probiotics in preventing further UTIs.
Additionally, Dr Williams and her collaborators found that ingesting cranberries or cranberry products doesn’t help reduce everyone’s risk of UTI. For example, cranberries did not seem to reduce UTIs in elderly institutionalised men and women, in adults with neuromuscular bladder dysfunction and incomplete bladder emptying, or in pregnant women.
They did find that few people reported any side effects from cranberries, with the most common being abdominal pain.
The clinical trials in the studies that the team reviewed varied in duration of cranberry consumption from 4 weeks to 12 months. As a result, Dr Williams and her collaborators were unable to identify whether cranberry tablets or liquids are more effective, what dosage of cranberry works best, nor how long people should take cranberry products to experience their full benefits.
Dr Williams and her collaborators recommended further assessment in well‐designed randomized controlled trials to further clarify who with a risk for repeated UTIs would benefit from cranberry products and the effective dosage.
Gabrielle Williams, Deirdre Hahn, Jacqueline H Stephens, Jonathan C Craig, and Elisabeth M Hodson (2023). Cranberries for preventing urinary tract infections, Cochrane Database of Systematic Reviews April 17;4(4):CD001321 | doi:10.1002/14651858.CD001321.pub6