Can a glass of cranberry juice a day keep the urologist away? You might have heard that cranberries help prevent urinary tract infections (UTIs), but are these berries really as medicinal as they are tart and tasty?
There is some science behind the claims that cranberries can protect against urinary tract infections, especially in women who are prone to getting UTIs. Yet the benefit for other groups of people isn't as clear. Plus, there are no real recommendations on how much cranberry juice you'd need to drink to get any protection against UTIs.
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Here's a look at the research on cranberries for urinary tract health and what the health experts have to say about their benefits.
Cranberries: The Science Behind Urinary Tract Protection
Scientists used to believe that cranberries protected against UTIs by making the urine more acidic and, therefore. inhospitable to bacteria like Escherichia coli (E. coli) that cause urinary tract infections. Now the thinking has shifted.
Researchers now believe that cranberries contain substances that prevent infection-causing bacteria from sticking to the urinary tract walls. There are a couple of different theories about how exactly cranberries do this. Some studies show that certain antioxidants in cranberries change the bacteria so that they can't stick to the urinary tract. Another idea is that cranberries create a Teflon-like slippery coating on the urinary tract walls that prevents E. coli from getting a good grip.
Do Cranberries Really Prevent UTIs? The Evidence
Studies that have analyzed the effects of cranberry products on urinary tract infections have gotten mixed results. Here's an overview of the evidence:
A few studies have found that drinking cranberry juice or taking cranberry pills can prevent UTIs, especially in women who are at risk for these infections:
One study looked at women who had a history of urinary tract infections caused by E. coli bacteria. Women who drank 1.7 ounces of cranberry-lingonberry juice concentrate every day for six months lowered their risk of getting a UTI by 20% compared to women who didn't use any intervention.
In another study, cranberry juice and cranberry tablets were linked to fewer patients who experienced at least one symptomatic UTI. In the study, sexually active women took one tablet of concentrated cranberry twice a day, drank about 8 ounces of pure unsweetened cranberry juice three times a day for 12 months, or were given a placebo.
In a third study, older adults who ate cranberry products were about half as likely to have bacteria and white blood cells in their urine in the setting of no UTI symptoms -- a sign of urinary tract infections. But other studies in older people showed no difference in symptomatic UTI in people using cranberry and those who didn’t.
Before you rush out and buy cartons of cranberry juice, there are a few caveats you should know about.
First, cranberries don't seem to work for everyone. Although they may appear to help prevent symptomatic urinary tract infections in some women who are at risk for them, there's no real evidence that cranberries offer any benefit to other groups of people, such as children or seniors.
Cranberries don't prevent bacteria from growing in the urinary tract -- they just make it harder for the bacteria to take hold. Cranberry juice also doesn't treat urinary tract infections once they've started.
Because of their acidity, cranberries can be hard for some people to take. Up to half of people in studies dropped out because of unpleasant side effects like gastroesophageal reflux disease (GERD), upset stomach, nausea, and diarrhea. Many people in the studies also balked at the tart-sweet taste day after day. People who don't like cranberry juice might find cranberry tablets easier to swallow.
In addition to its positive effects, cranberry juice can also have a negative effect on the urinary tract. Cranberry juice is high in salts called oxalates. When people drink a lot of cranberry juice, these salts can crystallize into hard urinary oxalate stones, especially in people who already tend to get these types of stones.
People who take the blood-thinning medication warfarin should avoid cranberry products because cranberries can interact with warfarin and cause excess bleeding.
Drinking cranberry juice or taking cranberry pills isn't cheap. The cost can add up to $1,400 a year for cranberry juice and $624 a year for pills.