The science of cranberry: How proanthocyanidins (PACs) prevent bacterial adhesion

Many people assume cranberry juice helps with UTIs because of its acidity, and while cranberry juice can slightly affect urine acidity, that’s not the primary reason it’s studied for urinary health. Instead, research has focused on naturally occurring cranberry compounds, including proanthocyanidins (PACs), and how they may support urinary tract health.

PACs work at the microscopic level by interacting with certain bacteria in ways that may help reduce their ability to cling to the bladder wall. Scientists also believe that when PACs appear in urine, they may help reduce how easily UTI-causing bacteria can stick to the lining of your bladder.[1, 2]

In this article, we'll explore exactly how PACs work, what makes cranberry PACs different from those in other foods, and why standardized cranberry supplements with PACs may offer a more consistent way to incorporate these compounds than juice alone.

Understanding UTIs: Why bacterial adhesion matters

UTIs happen when microorganisms — most commonly the bacteria E. coli — attach to bladder cells, multiply, and form sticky colonies (biofilms) that are surprisingly hard to flush out. E. coli is responsible for most urinary tract infections, and these bacteria have hair-like structures called pili that allow them to attach to the lining of the bladder and other parts of the urinary tract.[3]

Once bacteria attach, they don't just sit there. They form something called biofilms — protective layers that help them resist both your body's natural defenses and antibiotics..Biofilm-forming bacteria play a role in up to 80% of all microbial infections, and urology is one of the main fields where biofilm can become a serious problem.[4]

Biofilms are also discussed in studies exploring why some people experience recurrent UTIs. Research suggests that the ability of certain microorganisms to form biofilm may help explain why some individuals are more prone to recurring infections.[4]

Here's the important part: many studies focus on the initial adhesion step because it plays a role in the early stages of UTI development. Cranberry has been studied for its potential anti-adhesion properties, meaning its compounds may help reduce how easily certain bacteria can stick. Research points to A-type PACs in cranberries as the key compounds associated with this effect.[4]

Meet the molecules: What exactly are PACs?

Proanthocyanidins (PACs) are polyphenols,  naturally occurring plant compounds, found in various foods like grapes, apples, and chocolate. However, only cranberries (and to a lesser extent, lingonberries) contain A-type PACs in significant amounts — the specific kind linked to urinary health benefits. Fresh cranberries provide significant levels of these compounds, which is believed to contribute to their unique role in urinary wellness.[5]

In laboratory and clinical research settings, these compounds have been studied for how they may interact with certain structures on the surface of bacteria such as E. coli.[4] Rather than killing bacteria or treating an infection, this interaction is one reason researchers are interested in cranberry compounds when discussing urinary tract health support.

How cranberry PACs prevent bacteria from sticking

Let’s take a closer look at what researchers have studied so far. PACs have been examined in lab studies and in urine samples collected from people after consuming cranberry products to understand how they interact with certain bacteria, including E. coli.[2] One way to think about this interaction is like disrupting Velcro before it fully sticks. Rather than treating an infection, these findings help explain why cranberry compounds are often discussed in the context of supporting urinary tract health.

What makes A-type PACs unique is their structure, and researchers believe this may influence how they interact with certain bacteria in the urinary tract.[6]

Research in this area is still evolving. Some small, exploratory studies have examined how cranberry consumption may influence bacterial behavior in urine samples collected from people after intake.[7]

In these studies, researchers observed changes in bacterial interactions in laboratory testing, though results varied across time points and study designs.[8]  Because this type of research is preliminary and some is  conducted outside the body, it helps inform scientific understanding but does not prove clinical prevention.

In other words, when researchers tested the urine of people who had consumed cranberry, those samples showed changes in how bacteria behaved in a laboratory testing.

What happens in your body after you have cranberry

After you consume cranberry products, your body processes cranberry-derived compounds, and some of these compounds or their metabolites may later be detected in urine.[6,9] Researchers study this pathway to better understand how cranberry consumption relates to urinary wellness, though many details are still being explored.[6]

Because research in this area often involves laboratory testing of urine samples collected after intake, findings help inform scientific understanding rather than establish treatment or prevention outcomes.[2] For this reason, cranberry is generally discussed as a supportive option within a broader urinary wellness routine. It is not as a one-time fix or a substitute for medical care.

Form, consistency, and what matters most when taking cranberry

So what actually matters when it comes to cranberry? Rather than focusing on a specific compound or measurement, using cranberry consistently and choosing high-quality products as part of an overall urinary wellness routine is more important.

In fact, the FDA has authorized a qualified health claim stating: Consuming 500 mg each day of whole cranberry fruit powder may help reduce the risk of recurrent urinary tract infection (UTI) in healthy women. FDA has concluded that there is limited scientific evidence supporting this claim.[10]

When choosing between cranberry juice and supplements, form can make a difference. Cranberry supplements are often used for their convenience and consistency, since they provide concentrated whole cranberry ingredients in a small serving without the added sugars commonly found in juice. Cranberry juice can still contribute to hydration and cranberry intake, but its cranberry content can vary widely between brands and blends.[1]

If you choose to include cranberry in your routine, using it regularly is generally recommended. Cranberry works best alongside other healthy habits, like staying well hydrated and practicing good bathroom hygiene, rather than on its own.

It’s also important to understand what cranberry can and can’t do. Cranberry products are not a treatment for UTIs. If you’re experiencing UTI symptoms such as burning, urgency, or pain, it’s important to see a healthcare provider. A UTI will not resolve on its own, and cranberry products should not be used in place of antibiotics when an active infection is present.

Think of cranberry as a supportive option for urinary tract health, guided by FDA-recognized evidence, when used consistently as part of a broader wellness approach.

FAQs

Are all PACs the same?

Not exactly. PACs exist in different plant foods, but only A-type PACs — the kind found in cranberries — have been shown to prevent bacterial adhesion in the urinary tract.[4]  Other foods like grapes and chocolate contain B-type PACs, which don't have the same structural properties or anti-adhesion effects. This is why cranberry specifically is studied for UTI risk reduction, while other PAC-rich foods aren't necessarily recommended for urinary health.

Do PACs kill bacteria directly?

No, PACs don't kill bacteria. Instead, they’ve been studied for how they may influence bacterial behavior, including how certain bacteria interact with or attach to surfaces in the urinary tract.[1]  This research helps explain why cranberry is often discussed in the context of urinary wellness support rather than as a way to kill bacteria or treat an infection.

Cranberry products are not a treatment for active infections. If you have UTI symptoms, it’s important to see a healthcare provider for proper diagnosis and care.

Can cranberry PACs replace antibiotics?

No. Cranberry PACs cannot replace antibiotics. If you have an active UTI, you need antibiotics prescribed by a healthcare provider.[1] Cranberry products are not a treatment for infections and cannot cure a UTI once symptoms are present. If you think you may have a UTI, it’s important to seek medical care promptly rather than relying on cranberry alone.

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