Although cranberry juice and capsules are popular antidotes to the common bacterial infections, researchers haven't always been sure whether or how they might work. Recent evidence suggests certain compounds in cranberries - and maybe other berries as well - might prevent bacteria from attaching to tissue in the urinary tract, thereby warding off infections.

"What this is doing is solidifying what has been folklore for quite some time," said Dr. Deborah Wing, who has studied urinary tract infections at the University of California, Irvine.

"Finally, the science is catching up to what our mothers have been telling us for so many decades," she told Reuters Health.

Still, Wing noted some women have trouble drinking a lot of cranberry juice or don't like swallowing the large capsules. There's also a lack of data about what form of cranberries - juice versus capsules, for example - is easier to take and better for reducing UTI risk, said Wing, who wasn't involved in the study.

For the new analysis, researchers led by Dr. Chih-Hung Wang from National Taiwan University Hospital consulted 10 earlier studies of about 1,500 people, mostly women, who were randomly assigned to take daily cranberry products, cranberry-free placebo products or nothing.

The amount of cranberry compounds used in the studies varied greatly, from one-gram capsules to close to 200 grams of cranberry juice daily. Overall, participants assigned to cranberry products had 38 percent fewer UTIs, the research team reported Monday in the Archives of Internal Medicine.

For women with a history of multiple infections, in particular, the risk of UTI was reduced by 47 percent while on cranberry products. For example, in one study of Canadian women with recurrent infections, there were 19 UTIs among 100 women taking both cranberry capsules and juice over a year, compared to 16 infections in 50 women who were assigned to cranberry-free imitation juice.

Because of differences between the trials and questions of how well participants and doctors were "blinded" to who was getting what product, Wang and colleagues said the findings "should be interpreted with great caution."

"Is (cranberry) the natural cure-all for urinary tract infections? Of course not," said Bill Gurley, a pharmaceutical researcher who has studied dietary interventions at the University of Arkansas for Medical Sciences in Little Rock.

"For individuals that do have problems with recurrent UTIs, incorporating a little cranberry juice in your diet certainly can't hurt," added Gurley, who wasn't part of the new research team. Still, he told Reuters Health, "We still don't know exactly what the correct dose should be, or what the correct form should be."

Wing said certain women are predisposed to UTIs. Those who are born with a malformed urinary tract or engage in anal sex, for example, are also at higher risk of recurrent infections.

Cranberry juices and capsules are an attractive option for preventing UTIs because unlike with antibiotics, taking the products for long periods of time doesn't increase the risk that drugs used to treat infections will stop working when bacteria build up resistance.

Cranberry tablets are also relatively cheap, starting at about 25 cents per day. However, one recent study found antibiotics were still more effective at preventing infections in Dutch women with recurrent UTIs (see Reuters Health story of June 25, 2011).

High doses of cranberry products can also cause stomach aches - and the sugar in juice might be a problem for people with diabetes, the researchers noted.

Until the science catches up, Wing said, for women who want to try cranberry products the decision of juice versus capsules "is a matter of personal preference" - as long as they look carefully at product labels and know that not all over-the-counter juices and capsules are created equal.

SOURCE: bit.ly/OdmdoZ Archives of Internal Medicine, online July 9, 2012.

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