October 8, 2026, 6:25 pm | Read time: 5 minutes
Cranberry juice is considered a popular remedy for preventing urinary tract infections. Many women who frequently struggle with bladder infections swear by it. However, studies have shown varying results regarding its actual effectiveness. Researchers at the University of Florida have now investigated why this might be the case. The hypothesis: Cranberry juice does not work the same for all women.
Different Reactions to Cranberry Juice
The study shows that women react very differently to cranberry juice. After four days, the ability of the urine to prevent certain bacteria from adhering to bladder cells improved in 40 of the 150 women in the study. The remaining women did not show a sufficiently strong improvement. The results could explain why previous studies on cranberry products have yielded different outcomes.
How the Study Was Conducted
Urinary tract infections are often caused by certain intestinal bacteria. When these enter the urinary tract, they can adhere to cells there. This is an important step in the development of an infection. Cranberry products are supposed to make it harder for the bacteria to adhere.
The researchers at the University of Florida wanted to find out why this effect might not be equally strong in all people. They examined how well the urine of different women prevented the bacteria from adhering and whether this effect changed with cranberry juice.1
Initially, 152 healthy women aged 21 to 65 participated. For ten days, they were to avoid cranberry products and certain other foods containing similar plant compounds. They then provided a urine sample. Afterward, the women drank nearly 300 milliliters of unsweetened cranberry juice daily for four days. A total of 150 women completed the study and provided another urine sample. In the lab, researchers then checked whether anything had changed after the cranberry juice. Specifically, they wanted to know if the urine could prevent certain E. coli bacteria, which often cause urinary tract infections, from adhering to bladder cells.
Why Some Women React More Strongly
Even before the cranberry juice, there were significant differences among the women. In some, the urine prevented the bacteria from adhering much more effectively than in others. The researchers therefore divided the participants into two roughly equal groups based on their initial values.
This showed a correlation with the later reaction to the cranberry juice: Women whose urine initially hindered the bacteria less frequently reacted positively. In this group, about 34 percent experienced this effect. Among women whose urine already showed a stronger effect at the beginning, it was about 19 percent.
Additionally, the researchers examined the composition of the urine of selected participants. Here, too, they found differences between women with initially stronger and weaker effects against bacterial adhesion. They identified specific metabolites in the urine (such as D-Glucaro-1,4-lactone with high protective effect) that are associated with the different protective reactions. The exact significance of these differences and how these substances in the urine influence the effect need to be explored in further studies.
It is also important to note: The researchers did not study actual urinary tract infections. They only measured in the lab how well the urine prevented bacteria from adhering to bladder cells. Whether the observed differences lead to some women experiencing fewer urinary tract infections due to cranberry juice cannot be concluded from the study.
The results could be especially important for future studies. If researchers consider that women differ even before taking cranberry products and react differently to them, their potential effects could be examined more precisely.
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Strengths and Weaknesses of the Study
A strength of the study is the relatively large number of participants for such a laboratory investigation. Additionally, the urine samples were examined under as similar conditions as possible, and measurements were conducted multiple times.
Nevertheless, the significance is limited. Since there was no control group, it cannot be said with certainty whether the changes were actually caused by the cranberry juice. Moreover, the study lasted only four days and only considered a specific type of bacterial adhesion (P-fimbriated E. coli). These are associated with bladder infections and particularly severe urinary tract infections like kidney infections, but they are not the only pathogens that can cause these diseases.
Furthermore, more than half of the participants were from a younger age group (21 to 35 years), and their daily diet and physical activity during the study days were not recorded. Also, the classification of women based on their presumed susceptibility to urinary tract infections was only established for this study. Whether it reflects the actual risk of disease is unclear.
The study was publicly funded and supported by a research fund from the University of Florida. The authors reported no conflicts of interest.
Also of interest: These foods are good for vaginal flora
What Previous Studies Show
Whether cranberry products protect against urinary tract infections has been studied for decades. A large review by the Cochrane Collaboration in 2023 evaluated 50 studies with nearly 9,000 participants.2 According to this, cranberry juice or capsules reduced the risk of recurrent urinary tract infections in women by more than a quarter. In older people, pregnant women, and individuals with bladder emptying disorders, no benefit was observed. The results of the individual studies also varied greatly.
A similar conclusion was reached by an analysis by Australian researchers in 2024, which focused on cranberry juice.3 In 20 studies with around 3,000 participants, those who drank juice experienced urinary tract infections significantly less often and required antibiotics less frequently. Here, too, the researchers rated the data’s significance as only moderate to low.