In recent years, research has confirmed that cranberries can help prevent urinary tract infections (UTIs)—a finding that draws on traditional knowledge dating back thousands of years, even if such claims have often been a subject of debate within the scientific community.
It now appears that the very same compounds that make cranberries effective against urinary tract infections may also benefit an entirely different aspect of human health: oral hygiene.
In a study published in the journal Scientific Reports, researchers discovered that consuming cranberry juice seems to inhibit the growth of dental plaque—a result that may come as a surprise to some.
“Most people perceive cranberry juice as being highly acidic—very tart and sweet—and therefore assume it couldn’t possibly have a positive impact on oral health,” says pediatric dentist Christine Wu of the University of Illinois at Chicago. “This study has shown the opposite.”
Cranberries contain compounds called proanthocyanidins (PACs), which can suppress bacterial infections. In the case of urinary tract infections, the proanthocyanidins found in cranberry juice can make it difficult for E. coli bacteria to attach themselves to the cells lining the bladder.
However, emerging evidence suggests that these proanthocyanidins may also help protect the oral cavity by inhibiting bacteria such as Streptococcus mutans. These bacteria accumulate in the plaque that forms on teeth and produce acids that contribute to the development of tooth decay. To determine whether the proanthocyanidins found in commercially available cranberry juice might offer a protective effect, Wu and his colleagues conducted a small study involving eight adults and 14 children.
In a randomized crossover study, participants consumed three different beverages on separate days: pure cranberry juice, a sweetened cranberry drink containing 27 percent cranberry juice, and water (as a control).
At each stage of the study, participants refrained from oral hygiene practices for 24 hours, after which a swab was taken from one side of their mouth to check for dental plaque.
Following this initial swab, participants consumed their assigned test beverage—swishing it around in their mouths before swallowing. Thirty minutes later, the researchers took a second swab of dental plaque from the opposite side of the participants’ mouths.
When the team compared the baseline swabs with those taken after the cranberry juice consumption, the results showed that pure cranberry juice reduced bacterial growth by 44 percent; among the child participants, a 33 percent reduction was observed compared to the baseline.
“The greater numerical reduction observed in adults may reflect age-related differences in the composition of dental plaque, which lead to varying susceptibility to the antimicrobial compounds found in cranberries,” the researchers explain in their paper. “Recent studies have demonstrated clear age-related differences in the composition, diversity, and abundance of the oral microbiome, with distinct microbial communities contributing to the development of dental caries in adults and children.” The regrowth of dental plaque bacteria following exposure to a sweetened 27% cranberry juice was numerically lower than it had been prior to exposure, though the difference was not statistically significant.
In addition to inhibiting bacterial growth, pure cranberry juice also significantly reduced acid production within the dental plaque of study participants—a finding that potentially limits the harmful effects these acids can have on tooth enamel.
Although the researchers did not specifically test this, they hypothesize that pure cranberry juice outperformed the sweetened cranberry beverage due to a higher concentration of proanthocyanidins; however, further research is required to confirm this.
It is worth noting that this was a very small-scale study. Furthermore, the researchers did not assess whether consuming cranberry juice protected participants from tooth decay over time, as the study focused exclusively on measuring dental plaque activity and acidity levels during the experiment.
Another point to consider is whether the high acidity of the juice could potentially damage teeth. That said, the researchers note that existing evidence regarding dental erosion caused by acidic beverages is inconsistent, and some studies even suggest that consuming cranberry juice may actually reduce dentin erosion.
Given that dental plaque activity and acid production are two primary drivers of tooth decay, these findings offer preliminary evidence that cranberries may function as a “functional food”—a food that provides oral health benefits extending beyond basic nutritional value.
More One potential cause for concern is its sour taste: researchers have noted that the low sugar content in cranberry juice may limit its appeal to people, especially children.
“In the future, the inclusion of non-cariogenic sweeteners could improve its acceptability without compromising safety or efficacy,” they suggest.
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