Up to 60 percent of women will experience at least one urinary tract infection (UTI) in their lifetime, and if you've ever had one, you'll know how unbearable it can be.

For years now, some doctors have been recommending cranberry juice and tablets to patients as a way to either prevent recurring UTIs or treat the symptoms, but a new study has found no difference between people treated with cranberries or placebos.

In fact, if you look back at all the scientific literature on the subject, you'll find that either the recommended amount of cranberry juice is far beyond what's realistic for an actual human being, or that there's no solid evidence that any amount is having a positive effect.

"[C]linicians should not be promoting cranberry use by suggesting that there is proven, or even possible, benefit," Lindsay E. Nicolle, an expert on UTIs from the University of Manitoba, wrote in an editorial accompanying the new study

"It is time to move on from cranberries."

The study, led by infectious disease specialist Manisha Juthani-Mehta from the Yale School of Medicine, investigated the effects of high-dose cranberry capsules - the equivalent of 591 ml (20 ounces) of juice every day - on 185 women in a nursing home.

Elderly women were chosen as the sample because among nursing home residents, UTIs are the most commonly diagnosed infection. 

Up to half of all women living in nursing homes test positive for bacteriuria (bacteria in the urine), and 90 percent of those will test positive for pyuria (the presence of bacteria and white blood cells in the urine). Those two symptoms combined are good sign that a UTI is present. 

The participants were split into two groups, and randomly assigned either two cranberry capsules a day - each containing 36 milligrams of the active ingredient proanthocyanidin - or a placebo.

Before the study had begun, 31 percent of the participants had tested positive for bacteriuria plus pyuria in their urine.

After 360 days of taking either the placebo or the cranberry capsules, the participants had their levels of bacteriuria and pyuria measured. 

The researchers found no difference in the presence of bacteriuria plus pyuria between the cranberry group and the placebo group, and they found no differences in the number of UTI episodes either. (Thirty-eight participants ended up dropping out the study because the daily capsules were too much of a hassle, or had died for unrelated reasons, so the results are based on the remaining 147 participants.)

"The continuing promotion of cranberry use to prevent recurrent UTI in the popular press or online advice seems inconsistent with the reality of repeated negative studies or positive studies compromised by methodological shortcomings," says Nicolle

"Any continued promotion of the use of cranberry products seems to go beyond available scientific evidence and rational reasoning."

For anyone following the UTI-cranberry juice saga closely, these results will not be a surprise - a lack of evidence for cranberry juice or capsules as being an effective preventative measure or treatment has been a recurring theme in the scientific literature for years.

In fact, as Susan Scutti reports for CNN, a 2012 review of 24 studies totalling 4,473 participants found little evidence of positive effects, and concluded that cranberry juice "cannot be recommended for the prevention of UTIs".

Given that Ocean Spray's cranberry juice cocktail is only 27 percent juice, it makes sense that something so watered down would be so ineffective, but based on the results of this recent study, even if you ramp things up by switching to highly concentrated capsules, you still don't see a discernible effect.

So why has this myth persisted for so long? There's a couple of reasons - firstly, the active ingredient in cranberries, A-type proanthocyanidins (PACs), have been shown to block the adhesion of bacteria to the wall of the bladder.

So a reasonable hypothesis is that if bacteria are causing UTIs, something that blocks them from accumulating in the bladder could be a potential treatment or preventative measure.

"For a UTI to occur, bacteria must adhere to and invade the lining of the bladder," Timothy Boone from the Texas A&M College of Medicine, who wasn't involved in the study, told Newswise. "PACs interfere with the bacteria's ability to bind to the wall of the bladder and create an infection."

But there's one problem. "It takes an extremely large concentration of cranberry to prevent bacterial adhesion," says Boone. "This amount of concentration is not found in the juices we drink. There's a possibility it was stronger back in our grandparents' day, but definitely not in modern times."

And now we have evidence that the concentration of PACs in capsules is also not strong enough to prevent bacteria from accumulating in the bladder.

The second reason the myth is so persistent is it's such a tempting myth to believe. If you experience recurring UTIs and want to prevent them, or you want to feel empowered while you're waiting for the antibiotics to kick in, drinking cranberry juice or taking capsules is a pretty easy way to feel like you're helping. 

At best, though, you're paying a lot of money for something that's only really doing the same job as a glass of water.

"It can offer more hydration and possibly wash bacteria from your body more effectively, but the active ingredient in cranberry is long-gone by the time it reaches your bladder," says Boone.

So save your cash and ditch the cranberry juice. It's full of sugar anyway.

The study has been published in the Journal of the American Medical Association, and the accompanying editorial is here.