DOES IT WORK:Cranberry juice has long been regarded as useful in treating and preventing UTIs, writes Dónal Ó Mathúna
CRANBERRY JUICE has long been recommended for the treatment and prevention of urinary tract infections (UTIs). The symptoms of a UTI range from cloudy urine, discomfort during urination and generally feeling unwell, to generalised groin pain and fever.
While anyone can get a UTI, they are 50 times more common in adult women than in adult men. One in four women who gets a UTI will have recurrent infections.
Conventional treatment for UTIs is with antibiotics, but with concerns about long-term use of antibiotics and antibiotic resistance, there is much interest in alternative strategies to prevent and treat UTIs.
Cranberry juice has been commonly recommended, although many people dislike its taste. For this reason, cranberry supplements have come on to the market which put cranberry concentrate into capsules or use dried cranberry extracts.
Evidence from studies
In the mid-1800s, it was noted that people who drank cranberry juice had more acidic urine. It was believed that this made the urine less favourable for the growth of bacteria. Studies have since noted that the acidity of urine is not the relevant factor, but that cranberry juice contains compounds which prevent bacteria from attaching to the walls of the urinary tract.
The first controlled study of cranberry juice was published in 1994. Elderly women who daily drank 300ml of cranberry juice had fewer UTIs than those drinking a similar-tasting red drink.
A few years later, another controlled study found no differences in the rates of infection between those drinking cranberry juice and those drinking a placebo drink. However, the second study involved children, not adults.
A systematic review of cranberry juice was published earlier this year in the Cochrane Library. This resource provides independent reviews of many interventions, both conventional and alternative. The Health Research Board has paid to make this library available for free on the internet anywhere in Ireland (see thecochranelibrary.com).
The Cochrane review found nine studies of cranberry for the prevention of UTIs. Overall, these found evidence that women who suffer from recurrent UTIs are most likely to benefit from the consumption of cranberry juice.
Over a 12-month period, such women had fewer UTIs than those taking a placebo. However, not everyone benefits from cranberry juice. Children and adults with catheters (another group at higher risk of UTIs) did not benefit from cranberry.
Another Cochrane review found no controlled studies of cranberry juice for the treatment of UTIs.
Problematic aspects
The studies did not identify serious adverse effects with cranberry juice, but many people did not complete the studies. In some cases, more than half the participants withdrew from the studies. This suggests that many people dislike cranberry juice or have difficulty drinking it daily.
This is a problem, since the juice must be taken daily for months or years. As a result, numerous tablet and capsule formulations are now on the market, but the evidence for their effectiveness is more limited.
Little information is available on how much juice to consume. The amount of juice used in the studies varied from 30ml/day to 300ml/day, with none of the studies explaining why they picked the dose they used. Four of the studies used cranberry supplements, but again the type and amount varied considerably. Products are not standardised against any active ingredient, making it impossible to make recommendations about the optimal dosage.
Recommendations
The evidence supports the use of daily cranberry juice to prevent UTIs among women with recurrent UTIs. The evidence is much less clear for any other group of people.
The amount needed for benefit is not clear, but a large glass of juice daily is probably sufficient. The evidence for any tablet or capsule formulation is much weaker.
Once someone has a UTI, there is no evidence that it can be treated effectively by cranberry juice. Conventional care should be pursued at that point.
• Dónal Ó Mathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University