Sugary drinks disrupt the composition of the salivary microbiome

A recent study published in Scientific Reports reports potentially pathogenic changes in the oral microbiota after consuming sugar-rich beverages.

Oral microbiome and sugar-sweetened beverages

The oral microbiome includes more than 700 species of bacteria, as well as fungi, viruses and other microorganisms. A disruption of the oral microbiome is associated with oral diseases such as periodontitis, and may also be associated with the development of diabetes, cardiovascular disease and some types of cancer.

Saliva is often used to study the oral microbiome because it is easily accessible and stable. In addition, salivary composition may reflect changes secondary to other microbiomes or environmental influences.

Researchers in the current study were interested in determining whether sugar-sweetened drinks, including sodas and fruit juices, are harmful to the salivary microbiota. The high acidity and sugar content of these drinks can promote tooth decay and support the growth of certain bacterial taxa that thrive in acidic environments. These bacteria can also produce more acid from the breakdown of carbohydrates.

Changes in biofilm composition affect the structure of the tooth surface where oral bacteria live, thereby affecting the salivary microbiome. High levels of glucose and acid in saliva can also lead to inflammation and subsequent changes in the salivary microbiome.

Despite these documented associations, there is still a lack of research on exactly how sugar-sweetened beverages affect the oral microbiome.

Participant data was obtained from the Cancer Society of America (ACS) Cancer Prevention Study-II (CPS-II) and National Cancer Institute (NCI) Prostate, Lung, Colon, and Ovarian Cancer Screening Program. Saliva samples were collected from study participants between 2000 and 2002 and 1993 and 2001, respectively.

The current study recruited both cases and controls who did or did not develop head and neck or pancreatic cancer during follow-up, respectively. Each of these individuals was healthy at initial screening when they provided saliva samples.

In the PLCO group, a food frequency questionnaire was used to assess dietary intake over the past year. Sugar-sweetened beverages included orange or grapefruit juice, 100% fruit juices or blends, and other sugar-sweetened drinks such as Kool-Aid, lemonade, and soda.

In the CPS-II group, study participants reported their consumption of soda and other caffeinated drinks, lemonade, punch, iced tea, and fruit juices of all types. Thus, in both groups, fructose and sucrose were sources of fermentable sugar in the diet.

What did the study show?

The current study included 989 participants, 29.8% and 44.5% of whom did not consume sugar-sweetened beverages in the CPS-II and PLCO groups, respectively.

The highest intakes of sugar-sweetened beverages in the CPS-II and PLCO groups were 336 and 398 grams per day, respectively, which is equivalent to consuming more than one can of juice or soda per day. Higher consumption of sugar-sweetened beverages was common among men, smokers, nondiabetics, and those who consumed more calories. In the CPS-II group, these individuals were also more likely to have a higher body mass index (BMI).

The higher the consumption of sugar-sweetened beverages, the lower the richness of α-diversity of salivary microbiota species. Higher consumption of sugar-sweetened beverages was associated with greater relative abundance of taxa from the family Bifidobacteriaceae, including Lactobacillus rhamnosus and Streptococcus tigurinus.

In contrast, genera such as Lachnospiraceae and Peptostreptococcaceae were less abundant. The higher the consumption of sugar-sweetened beverages, the lower the abundance of taxa such as Fusobacteriales, including Leptotrichia and Campylobacter.

This correlation did not weaken after adjusting for organisms such as S. Mutans, which are associated with dental or gum disease, or those found in diabetes. Thus, other bacteria are also responsible for changes in the composition of the oral microbiota.

Conclusion

Increased consumption of sugar-sweetened beverages is associated with decreased bacterial richness and changes in the composition of the oral microbiota. Acid-producing bacteria become more abundant, while some commensals become less abundant with increasing consumption of sugar-sweetened beverages. This finding persisted after accounting for the presence of diabetes and oral disease, which can independently alter the composition of the oral microbiota.

When analyzing only individuals with subsequent cancer, the associations become weaker. This indicates that cancer risk factors are not responsible for these results.

Reduced richness of the salivary microbiome may limit its stability and resistance to environmental changes, thereby predisposing an individual to certain diseases. This may be attributed to the damaging effects of exposure to high-sugar and high-acid beverages or to poor oral health in consumers, which may include deep gum pockets, dental caries, and increased plaque accumulation.

It should be noted that markers of oral disease, such as S. Mutans, did not influence the study results. Indeed, the presence of S. Mutans may indicate the presence of dietary factors promoting its growth, as well as other cariogenic bacteria.

A decrease in commensal bacteria can negatively affect the innate immunity of the gums. The study also suggests that Lactobacilli and Bifidobacteria may not be ideal choices for oral probiotics because they produce acid that can potentially damage tooth structure.

Overall, the current study provides a better understanding of how microbiome-targeted dietary approaches can be used to prevent oral and systemic diseases.