Image of cranberries via Getty.

Health headlines were dominated last week by a study that seemed to confirm, once and for all, that cranberry juice cannot cure a urinary tract infection. The fact that the research study was actually on cranberry capsules and looked at prevention didn’t stop the coverage from reigniting a century-old debate around whether cranberry products can treat UTIs. The answer is no, of course they can’t, but you can hardly blame us for believing a piece of gynecologic advice passed down through generations of women.

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There are two separate issues here that, somewhere in the twisted game of telephone from research to doctor to patient, ended up being confused: prevention and treatment. Prevention happens before you get sick—in this case, the idea is that cranberries will stop you from getting a UTI. Treatment happens after you’re sick—it (hopefully) cures an existing UTI, restoring your urinary tract to its non-bacteria riddled happy state. So before we go deep into the science on this, I want to say up front that research is still unclear as to whether cranberry products can prevent UTIs. But there’s one place where research is not divided: cranberry is not a treatment. It does not cure UTIs once you have them. Chugging it will not miraculously clear up your bacterial infection. Taking the pills will not soothe the burning when you pee. If you have a UTI, you need a doctor, not the juice section of the grocery store.

One would think that in the age of internet, this myth would have died long ago, but it turns out that an overabundance of information can be equally confusing. The first result when you Google “does cranberry juice help urinary tract infections” is a WebMD article from 2010 titled “Cranberry Juice Fights Urinary Tract Infections Quickly” on a study sponsored by the Cranberry Institute and Wisconsin Cranberry Board. It’s not surprising that advice passed down by a friend, family member, or TV personality that is confirmed by a website with “MD” in the title is considered unassailable. I’m going to assail it, though.

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It’s easy to see why Big Cranberry wants you to think they can help with UTIs—it’s a thriving infectious industry. Urinary tract infections are incredibly common—more than half of otherwise healthy American women will have at least one UTI in their lifetime. In the United States alone, UTIs cost $3.5 billion a year and account for 1% of primary care visits. The cranberry cabal probably meets monthly to discuss funding research studies and planting pro-cranberry propaganda in internet comment sections.

The claims aren’t entirely unfounded, though; there are two theories behind why cranberry products would work to manage UTIs. The first involves making your urine more acidic (and therefore less hospitable to bacteria). This was initially discovered by German chemists in the 1840s and later reinforced by scientific research as far back as 1914. Recently, researchers have moved on from the acidification theory and instead suspect that, in high concentration, cranberry products (specifically proanthocyanidins) work by inhibiting the ability of bacteria to adhere to your uroepithelium (put more simply, it keeps bacteria from sticking to your urinary tract so that they can’t hang around to cause an infection). It bears mentioning that most of this research is done on E coli. While E coli is responsible for roughly 75% of UTIs in healthy adults, it is far from the only bacteria that causes it.

A lot of the modern “cranberries are a urinary tract superfood” hysteria can be traced to a 1994 study published in Journal of the American Medical Association (JAMA) that showed the possible benefit of using cranberry juice to prevent bacteriuria (bacteria in your pee) in elderly women. Despite several issues with the study, Ocean Spray Cranberries, Inc were off and running, brandishing the results as proof that their products offered more advantages than your average berry. Today, we have laws against companies openly lying about the health benefits of their products. In 2001, the FDA required Ocean Spray, Inc to remove claims that their cranberry products, among other things, improve urinary tract health. In 2009, the European Food Safety Authority prohibited the company from making claims that their products prevented UTI on products sold in the EU. In 2014, they issued a similar ruling to CranMax, another cranberry product making lofty claims about its effectiveness.

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Research looking at UTIs and cranberry shows no sign of stopping, though—there were more than a dozen studies on it this year alone (they did not look at treatment though because, again, cranberry juice can absolutely not treat a UTI). I limited the discussion here to studies on women—the research grows exponentially when you add children and men into the mix. The most recent study, published last week in JAMA, lends support to the “cranberries are not a magical bacteria killing berry” side of the conversation.

In this Yale University study, 185 women living in Connecticut nursing homes were randomly assigned to take either two oral cranberry capsules or placebo pills daily for one year. Every two months, a urine sample was tested for the presence of bacteria (bacteriuria) or white blood cells (pyuria). Researchers found there was no difference in rates of bacteriuria or pyuria between women given cranberry products and those given placebos. It’s an interesting finding, but there are a few reasons to think twice before applying it to women in general. For one, the small group of women studied are at particularly high risk for UTIs (older, post-menopausal women and those living in a care facility). For another, the primary outcomes they looked at (bacteria and white blood cells in the urine) aren’t typically treated in most women. Doctors do not routinely check for UTIs in healthy, non-pregnant women because bacteria in the urine may clear up on its own, avoiding unnecessary treatment. Outside of studies, UTIs are generally diagnosed when symptoms motivate someone to go to the doctor.

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Limitations notwithstanding, the study did find that cranberry capsules with a high proanthocyanidin content did not prevent UTIs in the population studied. And, while this study looked at a very specific population, it’s backed up by prior research as well. In 2011, a study looking at healthy college-aged women that found that drinking cranberry juice failed to prevent recurrent infections. Study author Dr Manisha Juthani-Mehta, associate professor of Infectious Disease at the Yale University School of Medicine, explains: “At this point, most of the evidence suggests that cranberry products, juice or capsules, don’t work. There is little downside to cranberry juice, and I believe that physicians still recommend it to offer a simple and relatively harmless intervention to patients that are looking for some alternative. The mainstay of UTI prevention should be hydration. Women at risk for recurrent UTI should try to drink several glasses of water per day. For many women, this intervention alone prevents recurrent episodes.”

These findings don’t go unchallenged. There are several studies suggesting that women with recurrent UTIs might benefit from regularly consuming cranberry products, including one published this year in the American Journal of Clinical Nutrition. Yes, Ocean Spray Cranberries, Inc both funded that study and employs two of the people who designed it, performed the research, and wrote the manuscript. Yes, I do think that we should view studies funded by corporations that will directly benefit from their findings with an entire shaker’s worth of salt. But, jokes about cranberry conspiracies aside, this is critical research. The concerns of antibiotic resistance worldwide cannot be overstated and anything that could possibly reduce the use of antibiotics (say, by preventing an infection that is frequently treated with them) needs our attention.

In hopes of settling this debate once and for all, a 2012 Cochrane Library review article looked at 24 prior studies evaluating the effectiveness of cranberry products in preventing UTIs. They concluded that, based on all of the available evidence, cranberry juice does not prevent infections in women with recurrent UTIs. There were conflicting studies on whether cranberry capsules and tablets may be as effective at preventing UTIs as antibiotics. That all seems decisive unless you read the other review (this time in the Archives of Internal Medicine) published that year that found that cranberry products may be protective against UTIs for certain groups of women. When credible journals provide opposing explanations of the same data, it’s hard to know what to believe.

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A 2016 article in Advances in Nutrition finally asked that the question that plagues anyone digging into the research on a hotly debated topic: How can the same evidence lead to conflicting advice? The authors’ conclusion basically boiled down to the fact that the 2012 reviews meshed together studies done on different groups of patients — in the same way that we can’t generalize results from a high risk group to low risk patients, you can’t just ignore those factors when comparing different studies. So whether cranberry products work for you may depend on your personal risk. The studies are also completely inconsistent on the amount of cranberry taken each day and for how long so we really have no idea what dosing may work.

Cranberry isn’t the only product people pitch as a DIY solution to UTIs. The sugar D-mannose is thought to operate like cranberries do — preventing e coli from sticking to the urinary tract. There are some studies on rodents and cells from the human urinary tract suggesting that this may work, but one study found that it might actually prevent your immune system from fighting the harmful bacteria on its own. Most importantly though, there is a real lack of research on humans using D-mannose. There are two small studies that suggest it may be as effective as antibiotics in preventing UTIs, but they both have major limitations and there isn’t enough data out there to talk about how the findings stand against criticism.

The takeaway of all this, according to Dr Christopher Zahn, vice president of practice at American College of Obstetrics and Gynecology (ACOG), is that “Following diagnosis by a healthcare provider, ACOG considers a three day course of antimicrobial medicine the most effective treatment of a UTI. Cranberry juice and supplements are commonly confused as a cure for UTIs, though no evidence currently suggests they will cure an existing UTI. However, the long term use of cranberry juice and supplements to prevent UTIs may be effective in women with recurrent UTIs. Studies are continuing to evaluate this subject to determine the exact amount of juice or pills needed and how long you need to take them to prevent infection are being studied.”

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In their patient guide to UTIs, ACOG does explicitly mention that cranberry juice and pills may decrease the risk of getting a UTI, but that the specifics are still being researched. There are no current plans to update the FAQ (neither to add more specifics on research nor to explicitly confront the pervasive myth of cranberry juice as curative) but “it is possible this might get another look through following the quarterly committee discussion.”

“But wait,” you say, “my anecdotal experience says that cranberry juice works like a charm!” While in some cases, a UTI may clear up on its own, Dr. Juthani-Mehta emphasizes the risks of relying on something like cranberry juice to cure an infection: “A friend once told me that when she had burning on urination, she started drinking cranberry juice, only to have her bladder infection progress to a kidney infection when she was a young woman. The initial symptoms went away, consistent with what others say which is that it makes them feel better. But it can’t eradicate the infection so it only progressed.”

In other words, don’t make treatment decisions based on an old wives’ tale. As for prevention, cranberry products may or may not be helpful for certain women with recurrent UTIs. Either way, down with big cranberry.