Cystitis cannot be protected against by drinking cranberry juice, scientists have said.
Many women have used the juice to treat mild forms of the condition, which is a stinging inflammation of the bladder, or to prevent infection recurring.
But now scientists in a review said they found no evidence that the juice, or supplements, can be used to prevent kidney or bladder infections.
The condition, normally brought on by a urinary tract infection (UTI), has been nicknamed “the honeymoon disease” as it can also be set off by irritation during sexual intercourse.
It was suggested that compounds in cranberries could stop bacteria adhering to cells lining the urinary tract and many websites and GPs have encouraged women with the inflamation to try cranberry juice, but analysis of the new findings from 24 studies of 4,473 participants went against this.
Four years ago, a review of 10 trials found women who took the juice or cranberry supplements suffered fewer UTIs than women who did not, but some studies examined in the new review revealed “small benefits” for recurrent infections, although the authors said these results were not statistically significant.
They said women would have to take two glasses each day for a long time to prevent just one infection.
There was no particular need for more studies studies of the effect because most studies done indicate a small benefit at best, with a big drop-out rate of participants.
One problem with evaluating these studies was that the level of active ingredients in the supplements was rarely reported so it was hard to say if levels would have been high enough to have an effect.
“More studies of other cranberry products such as tablets or capsules may be justified, but only for women with recurrent UTIs, and only if these products contain the recommended amount of active ingredient,” said lead researcher Dr Ruth Jepson, from the University of Stirling.
In another review, it was found deaths from serious conditions such as cancer or heart disease were not cut by general health checks, and researchers advised against a public health programme including them.
However, lead researcher Lasse Krogsboll, from the Nordic Cochrane Centre in Copenhagen, affirmed that the team was not saying doctors should stop performing tests or treatment.
Of 14 trials involving 182,880 people, some provided unreliable results, and the authors reported no evidence that general health checks reduced death rates in the long term, a conclusion based on nine reliable trials with 11,940 deaths.