November 5, 2026, 9:04 am | Read time: 6 minutes

How Cavities Form

Cavities develop when bacteria in dental plaque metabolize sugar and produce acids. This lowers the pH level in the mouth. If tooth enamel is frequently and over a long period exposed to such acid attacks, it loses minerals. Over time, this can lead to cavities.

Cavities are widespread in Germany. Among 35- to 44-year-olds, about 93 percent have had cavities at some point. The situation is much better for children: Only 22 percent of 12-year-olds have had cavities.¹

Are There Foods That Protect Teeth?

Researchers at the University of Illinois Chicago investigated whether cranberry juice can affect the regrowth of dental plaque and its acid production. The focus was on plant compounds in cranberries that influence how certain bacteria adhere to surfaces and form biofilms.

“Just as sugar-induced damage is related to diet, I am interested in how the foods and drinks we consume can combat harmful bacteria and benefit our oral health,” explains study leader Christine D. Wu in a university statement.²

The core finding: Unsweetened juice made from 100 percent cranberries slowed both the regrowth of plaque bacteria and their acid production in adults and children.

Children and Adults Participated in the Study

The research consisted of two small studies. Eight adults aged 18 to 64 and 14 children aged seven to twelve participated. In a crossover trial, participants go through different test conditions one after the other. This allows their results to be compared with their own baseline values.

The researchers tested three beverages:

• unsweetened juice made from 100 percent cranberries
• a cranberry drink with 27 percent juice and 32 grams of added sugar per serving
• water as a control drink

Participants arrived in the morning with the plaque from the previous night. Initially, researchers collected plaque from one side of the mouth. Then, participants drank a total of 30 milliliters of the respective beverage in three portions. Each portion was swished in the mouth for half a minute before swallowing. After 30 minutes, the team collected plaque from the other side of the mouth. In the lab, they then examined how much the bacteria had grown after two and four hours and how much acid they produced.

“It was important for us to conduct these tests with human participants and with products available on the market,” explains Wu. Most previous studies had used lab-made cranberry extracts. Additionally, few studies had been conducted with children.

What Is the Result of the Study?

After four hours, the growth of plaque bacteria was reduced by about 44 percent in adults and about one-third in children by pure cranberry juice. Compared to water and the cranberry cocktail, the differences were statistically significant. “From a dental perspective, this is an interesting indication of the active ingredients in the berry, the proanthocyanidins,” explains dentist Dr. Anne Heinz for FITBOOK.

The sweetened cranberry drink, on the other hand, did not achieve a statistically significant effect. “The added sugar in the cranberry cocktail seemed to negate the benefit,” says Dr. Heinz, noting that this difference is particularly relevant for parents: “Most cranberry drinks in the supermarket are exactly such sweetened nectars.”

Does This Mean Cranberry Juice Protects Against Cavities?

While the study showed that pure cranberry juice temporarily influenced two processes in dental plaque that play a role in cavity formation, it did not investigate whether participants actually developed cavities less frequently. “Only the metabolic activity of the plaque was measured, not the cavities themselves,” explains Dr. Heinz. “It is not yet evidence of fewer cavities.”

The research team also limits the results due to the small number of participants and the short study period. Larger and longer-term studies would need to show whether the observed effects actually impact cavity risk.

Wu still sees potential in using cranberry components for oral health in the future. The juice could possibly be considered a functional beverage, meaning a food that has a health effect beyond its basic nutritional value.

The Catch: Cranberry Juice Is Very Acidic

That plaque bacteria produced less acid after cranberry juice does not mean the juice itself is harmless to teeth. “Cranberry juice is one of the very acidic drinks,” warns Dr. Heinz. She refers to two lab studies with different results: In one, cranberry juice attacked the tooth substance. In the other, certain ingredients possibly protected the dentin beneath the enamel. However, since these were only lab experiments, no definitive conclusions can be drawn for everyday life. For the dentist, the key factor is how often and over what period the teeth come into contact with the drink: “Frequent sipping throughout the day is unfavorable for the enamel, no matter how healthy the juice sounds.”

Immediately after drinking, one should also not reach for the toothbrush. Acid can temporarily soften the tooth surface. If brushed directly afterward, the affected surface can be more easily abraded mechanically.

More on the topic

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Caries Through Training? Why Athletes Often Have Bad Teeth — and What Helps

How to Drink Cranberry Juice Tooth-Friendly

Dr. Heinz would not recommend cranberry juice as dental care or as a thirst quencher for children. However, those who enjoy it can still consume the drink occasionally.

The dentist recommends:

• choosing a small glass of unsweetened juice made from 100 percent cranberries,
• drinking the juice with a meal,
• not sipping it over hours,
• rinsing with water afterward,
• waiting a bit before brushing teeth.

Her conclusion: “The study is a nice indication that there is something interesting in cranberries, perhaps one day as an active ingredient in toothpaste or mouthwash,” says Dr. Heinz. “But a glass of juice does not replace a toothbrush.”

What Provenly Protects Against Cavities?

For healthy teeth, the well-known measures remain crucial, according to Dr. Heinz. These include:

• drinking water or unsweetened tea
• brushing teeth twice daily with fluoride toothpaste
• using age-appropriate amounts and fluoride levels in children’s toothpaste
• not consuming sugar and acid throughout the day
• regular check-ups with the dentist