Sugary drinks disrupt the salivary microbiome

By Dr. Liji Thomas, MDReviewed by Benedette Cuffari, M.Sc.Jun 12 2024

A recent study published in the journal Scientific Reports reports on potentially pathogenic changes in oral microbiota following the consumption of sugar-rich drinks.

Study: Altered salivary microbiota associated with high-sugar beverage consumption. Image Credit: A3pfamily / Shutterstock.com

The oral microbiome and sugary beverages

The oral microbiome comprises over 700 bacteria species, as well as fungi, viruses, and other microorganisms. Disruption of the oral microbiome has been associated with oral diseases like periodontitis and may also be involved in the development of diabetes, cardiovascular disease, and some cancers.

Saliva is often used to study the oral microbiome, as it is easily accessible and stable. Furthermore, the composition of saliva can reflect changes secondary to other microbiomes or external influences.

The researchers of the current study were interested in determining whether sugary drinks, including soft drinks and fruit juices, were harmful to the salivary microbiota. The high acidity and sugar content of these drinks can facilitate the development of caries and support the growth of certain bacterial taxa that proliferate in an acidic environment. These bacteria can also produce more acid from the breakdown of carbohydrates.

Altering biofilm composition affects the structure of the tooth surface that harbors oral bacteria, thereby impacting the salivary microbiota. High salivary glucose and acid levels can also lead to inflammation and subsequent alterations in the salivary microbiome.

Despite these documented associations, there remains a lack of research on precisely how sugary drinks affect the oral microbiome.

About the study

Participant data were obtained from the American Cancer Society (ACS) Cancer Prevention Study-II (CPS-II) Nutrition and National Cancer Institute (NCI) Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial cohorts. Oral wash samples were obtained from study participants between 2000 and 2002 and 1993 and 2001, respectively.

Both cases and controls who did or did not develop either head and neck or pancreatic cancer during follow-up, respectively, were selected for the current study. Each of these individuals was healthy at baseline when they contributed saliva samples.

A food frequency questionnaire was used in the PLCO group to evaluate dietary intake over the past year. Sugary drinks included orange or grapefruit juice, 100% fruit juices or mixtures, as well as other sugary drinks like Kool-Aid, lemonade, and soft drinks.

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

What did the study show?

The current study included 989 individuals, 29.8% and 44.5% of whom did not consume sugary drinks in the CPS-II and PLCO cohorts, respectively.

The highest consumption of sugary beverages in the CPS-II and PLCO cohorts was 336 and 398 grams/day, respectively, which is equivalent to more than one can of juice or soda daily. Higher intakes of sugar beverages were more likely among males, smokers, non-diabetics, and those consuming greater amounts of 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 sugary drinks, the lower the α-diversity richness of the salivary microbial species. Moreover, a higher intake of sugar-rich beverages was associated with a greater relative abundance of taxa in the family Bifidobacteriaceae, including Lactobacillus rhamnosus and Streptococcus tigurinus.

Conversely, genera like Lachnospiraceae and Peptostreptococcaceae were less abundant. The higher the intake of sugary drinks, the lower the abundance of taxa like Fusobacteriales, including Leptotrichia and Campylobacter.

This correlation was not weakened after adjusting for organisms like S. mutans, which is associated with dental or gum disease, or those found in diabetes. Thus, other bacteria are also responsible for the altered composition of the oral microbiome.  

Conclusions

Increased sugary drink consumption is associated with reduced bacterial richness and altered oral microbiome composition. Acid-producing bacteria are more abundant, whereas certain commensals are less abundant as the intake of sugary beverages increases. This finding persisted after considering the presence of diabetes and oral disease, which may independently change the composition of the oral microbiome.

When only individuals with subsequent cancers were analyzed, the associations became weaker. This indicates that risk factors for cancer were not responsible for these findings.

The reduced richness of the salivary microbiome may limit its stability and resilience to environmental changes, thus predisposing the individual to certain diseases. This may be attributed to the damaging effects of exposure to high-sugar and high-acid drinks or impaired oral health in these consumers, which may include deep gum pockets, dental caries, and increased plaque accumulation.

Notably, oral disease markers like S. mutans did not affect the study findings. Indeed, the presence of S. mutans may indicate the presence of dietary factors promoting its growth, as well as that of other cariogenic bacteria.

The reduction in commensal bacteria may adversely affect the innate immunity of the gums. The study findings also suggest that Lactobacilli and Bifidobacteria may not be ideal choices as oral probiotics, as they produce acid, which can potentially damage the tooth structure.

Overall, the current study provides a better understanding of how dietary approaches targeting the microbiome may be used to prevent oral and systemic disease.