The review in Archives of Internal Medicine looked at 10 head-to-head trials of cranberries versus no treatment in 1,500 volunteers.
But experts warn that the amount people must consume to gain this benefit – a couple of glasses daily for months or years – may be unacceptable to some. And it doesn’t work for everyone.
Cranberries contain a substance that can prevent certain bacteria from sticking on the walls of the bladder, studies show. These bacteria, called E. coli, cause over 80% of all urinary tract infections.
The researchers who carried out the latest review found cranberry juice and other products containing cranberries that are sold in pharmacies can ward off some of these E.coli infections.
But they don’t necessarily work every time or for all individuals.
They tend to work best in women experiencing recurrent urine and bladder infections. And juice appeared to be slightly better than capsules or tablets containing cranberry, although more efficacy studies are needed to confirm this.
The National Taiwan University Hospital researchers who conducted the review said more work was also needed to discover the optimum dose.
Laboratory studies have shown the anti-adhesion activity of cranberry on bladder bacteria lasts for around eight hours after ingestion, which suggests a few doses a day might be ideal.
But since cranberry juice has a high sugar content, this might not be advisable for general health.
In one of the 10 studies the researchers looked at the dose had to be reduced because many of the women participating in the trial disliked drinking three glasses of the juice every day.
Dr Ruth Jepson of the University of Stirling has been carrying out a similar review into cranberry juice.
She said: “I’m not sure how many of us would want to be drinking this every day for an indeterminate amount of time. It can be costly and calorific and some people just don’t like the taste of it.”
Doctors advise people with urinary tract infections to drink plenty of fluid and the problem will usually get better on its own. They may recommend a course of antibiotics.
Cranberry can interact dangerously with warfarin medication, so patients on this blood-thinning drug are advised to avoid cranberry products.
Source: BBC News
