The updated review – initially published in 1998 and last updated in 2008 – analyses the most up-to-date evidence from clinical trials investigating the usefulness of cranberry products for prevention of urinary tract infections (UTIs).
Led by Ruth Jepson from the University of Stirling, UK, the new review contrasts its 2008 findings that cranberry products have some benefit for UTIs, by now concluding that any benefit, if present at all, is likely to be small and only for women with recurrent UTI.
“Prior to the current update it appeared there was some evidence that cranberry juice may decrease the number of symptomatic UTIs over a 12 month period, particularly for women with recurrent UTIs,” write the researchers.
“The addition of 14 further studies suggests that cranberry juice is less effective than previously indicated.”
Jepson commented that she does not see ‘a particular need’ for more studies investigating the effects of cranberry juice, “as the majority of existing studies indicate that the benefit is small at best, and the studies have high drop-out rates."
The lead researcher noted that in many studies where participants were given juice, there were large numbers of drop-outs – suggesting that a daily juice might not be acceptable to drink over long time periods.
She added that a common problem with research evaluating cranberry tablets or capsules was that they rarely reported the levels of active ingredient, meaning it is unclear whether levels would have been high enough to have any effect.
"More studies of other cranberry products such as tablets and capsules may be justified, but only for women with recurrent UTIs, and only if these products contain the recommended amount of active ingredient," she added.
For the updated systematic review, the team gathered together evidence from 24 studies – involving a total of 4,473 people. This includes data from 14 more studies than the 2008 update.
The analysis revealed although some studies showed small benefits for women suffering from recurring infections, women would have to consume two glasses of cranberry juice per day for long periods to prevent one infection.
“Although some of small studies demonstrated a small benefit for women with recurrent UTIs, there were no statistically significant differences when the results of a much larger study were included,” says the review.
“Given the large number of dropouts/withdrawals from studies (mainly attributed to the acceptability of consuming cranberry products particularly juice, over long periods), and the evidence that the benefit for preventing UTI is small, cranberry juice cannot currently be recommended for the prevention of UTIs,” they conclude.
"Looking to future trials, we recommend no further trials of the juice should be done because it's probably not effective," said Jepson. "Instead research needs to evaluate properly standardised tablets or capsules to test whether they do have an effect and to provide clear insights into the dosage."
Supplements less affected
Doug Klaiber, C.E.O. of Decas Botanical Synergies (now part of Naturex), said while the review was not good news for juice, it's a different picture for supplements. Decas supplies PACran, a standardized cranberry supplement ingredient.
”The Cochrane report highlighted the deficiencies in the current published clinical research for cranberry juice but also presented the merits of cranberry supplements which are standardized in the active ingredient. The focus of our business and clinical research has been on standardized cranberry supplements," he said.
Marc Roller, Scientific Director of Naturex said delivering the active cranberry compounds via a supplement improves compliance.
"The daily PACran dose necessary to reach efficacy in UTIs si not as constraining as juices. This has been confirmed in all clinical trials performed with PACran , where dropouts were much lower than what was reported in other trials with cranberry juice," he said.
Source: The Cochrane Library
Published online, doi: 10.1002/14651858.CD001321.pub5
“Cranberries for preventing urinary tract infections”
Authors: Ruth G Jepson, Gabrielle Williams, Jonathan C Craig