Researchers found that cranberry juice made with high concentrations of proanthocyanidins (PACs) cut kids' risk of repeat urinary tract infections by two-thirds, versus a comparison juice.

Since the juice on your supermarket's shelves may not have that PAC level, the researchers say their findings are not an endorsement of any product.

But the results, published in the Journal of Urology, do give support to cranberry as a UTI fighter, according to a pediatric urologist not connected to the study.

PACs are the compounds thought to give cranberries their bacteria-fighting potential. Women have long turned to cranberry juice and supplements to help prevent recurrent urinary tract infections (UTIs) - though studies have been mixed on whether they work.

There has been little research on kids, even though UTIs are relatively common in children. Girls have about an 8 percent chance of contracting the infection at some point in childhood; boys have a 2 percent chance.

Besides being uncomfortable, recurrent UTIs can eventually damage the kidneys in some children. So doctors may prescribe antibiotics to help prevent them.

But antibiotics can have side effects, and using them long-term can breed drug-resistant bacteria. So researchers are looking at whether cranberry products can be a good alternative.

For the new study, doctors at the University of British Columbia in Vancouver, Canada, recruited 40 children who'd had at least two UTIs in the past year. They randomly assigned the kids to drink one of two juices made for the study: a cranberry juice rich in PACs or a juice free of all "cranberry products."

Over the next year, kids who drank cranberry juice had UTIs at a rate of 0.4 per child, compared with 1.15 in the comparison group.

The power of cranberries against UTIs "was initially regarded as an old wives' tale," said Dr. Hiep Nguyen of Boston Children's Hospital, who was not involved in the study.

But Nguyen said he now often recommends cranberry - either juice or supplements - when kids have recurrent UTIs.

"It can be a great alternative to prophylactic (preventive) antibiotics," Nguyen said.

That doesn't mean cranberry is the cure-all. If a child has frequent UTIs, Nguyen said, antibiotics may be necessary to "break the cycle." On top of that, many children's UTIs are related to less-than-ideal bathroom habits - like "holding it in," rather than going when they need to.

Drinking enough fluids, going to the bathroom regularly, and - if needed - tackling constipation problems are all considered important in warding off kids' UTIs.

So Nguyen cautioned parents against simply running to the grocery store for cranberry juice. "They still should see a doctor, so they can try to address the underlying problem," Nguyen said.

What's more, there's no guarantee that the cranberry juice you buy would have the PAC content that the juice in this study did.

"The findings of this study should not be construed as an endorsement of any commercially available cranberry products," write the researchers, led by Dr. Kourosh Afshar. (Afshar could not be reached for comment.)

Nguyen agreed that juice can be tricky. "Pure cranberry juice often doesn't taste so good," he noted. So manufacturers often mix it with something more palatable, like apple juice, or add a lot of sugar.

Cranberry juice mixed with other juices would likely have lower PAC levels. If there's added sugar, that means calories; drinking a lot of sugary juice can also cause diarrhea in kids.

"We do worry about the sugar content," Nguyen said.

So it would be important, he noted, not to overdo cranberry juice. In this study, the daily dose prescribed to each child was based on body weight.

Cranberry tablets are the other option. But no one knows the exact dose needed to prevent any one child's UTIs. Right now, it's basically a matter of following the product's labeling, according to Nguyen.

Six kids in each group of the study dropped out before they had completed it. The top reasons were the parents' belief that the juice wasn't working, and kids just refusing to drink it.

Getting children to drink cranberry juice can be a challenge, Nguyen noted - especially the pure variety without a ton of sugar.

Ocean Spray provided both juices used in the study. The work was funded by the Lions Gate Healthcare Research Foundation.

SOURCE: bit.ly/RpIBZm Journal of Urology, online August 20, 2012.

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